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### "A kinematical Erlanger Programme"

**Prof. Jose Figueroa-O'Farrill, University of Edinburgh**

**May 22, 2024 (Wednesday)**

Abstract: Klein’s famous Erlanger Programme can be summarised as “geometry from symmetry”. The geometries that Klein studied are “static” (time played no rôle). Adding time we arrive at a “kinematical” version of the Erlanger programme, which we could summarise as “physics from symmetry”. In this talk I would like to review the notion of kinematical groups and how given a kinematical group and via the study of some of its homogeneous spaces, we may arrive at the notions of particles and fields (both classical and quantum) and even gravity. This is, of course, well understood for the case of the Poincaré group, since that is the kinematical group underlying quantum field theory and general relativity, but the framework is more general and can be applied to other kinematical groups such as the Galilei and Carroll groups.

ITMP seminar will be held on Wednesday, May 22 at 18:00. The seminar will be organized via zoom.

Presentation

### "High energy scattering of strings in AdS"

**Maria Nocchi, University of Oxford**

**May 15, 2024 (Wednesday)**

Abstract: When studying string scattering in flat space, we rely on a world-sheet description, yet extending this to curved backgrounds poses nontrivial challenges. In this talk, we discuss how to compute string amplitudes on AdS as a curvature expansion around flat space and emphasize the pivotal role of single valuedness, akin to its significance in flat space. Specifically, we focus on the AdS Virasoro-Shapiro amplitude and start from its recent representation as a world-sheet integral. We take the next step towards a world-sheet theory in AdS by investigating the high-energy regime. As in flat space, this is accessed by saddle point techniques. Moreover, the path integral representation for the amplitude is dominated by a classical solution. Our algorithm computes AdS classical solutions to arbitrary order in a 1/R expansion, where R is the radius of AdS, in terms of single-valued multiple polylogarithms whose letters are the locations of the punctures. Finally, we show that AdS curvature corrections exponentiate in this limit.

ITMP seminar will be held on Wednesday, May 15 at 18:00. The seminar will be organized via zoom.

Presentation

### "Balance Laws as Test of Gravitational Waveforms"

**Prof. Lavinia Heisenberg, University of Heidelberg**

**April 24, 2024 (Wednesday)**

Abstract: Gravitational waveforms play a crucial role in comparing observed signals to theoretical predictions. However, obtaining accurate analytical waveforms directly from general relativity remains challenging. Existing methods involve a complex blend of post-Newtonian theory, effective-one-body formalism, numerical relativity, and interpolation, introducing systematic errors. As gravitational wave astronomy advances with new detectors, these errors gain significance, particularly when testing general relativity in the non-linear regime. A recent development proposes a novel approach to address this issue. By deriving precise constraints - or balance laws - directly from full non-linear GR, this method offers a means to evaluate waveform quality, detect template weaknesses, and ensure internal consistency. Before delving into the intricacies of balance laws in full non-linear general relativity, we illustrate the concept using a detailed mechanical analogy. We'll examine a dissipative mechanical system as an example, demonstrating how mechanical balance laws can gauge the accuracy of approximate solutions in capturing the complete physical scenario. While mechanical balance laws are straightforward, deriving balance laws in electromagnetism and general relativity demands a rigorous foundation rooted in mathematically precise concepts of radiation. Following the analogy with electromagnetism, we derive balance laws in general relativity. As a proof of concept, we employ an analytical approximate waveform model, showcasing how these balance laws serve as a litmus test for the model's validity.

ITMP seminar will be held on Wednesday, April 24 at 18:00. The seminar will be organized via zoom.

Presentation

### "Gravity and TTbar flows in higher dimensions"

**Prof. Roberto Tateo, University of Turin**

**April 10, 2024 (Wednesday)**

Abstract: We will discuss systems in arbitrary space-time dimensions where matter, deformed by TTbar-like irrelevant operators, is coupled to gravity in the Palatini formalism. We shall investigate the dynamically equivalent perspective, wherein the deformation transitions from the matter action to the gravitational one or vice versa. This alternative viewpoint leads to the emergence of Ricci-based gravity theories, thus providing a higher-dimensional generalisation of the well-known equivalence between 2d TTbar deformations and coupling to Jackiw-Teitelboim gravity. We shall examine this dynamical equivalence within the framework of the recently introduced Lagrangian flow equation, which has notably led to the discovery of a direct link between Nambu-Goto theory and TTbar and gave significant insights into nonlinear electrodynamics models in d=4. We will discuss explicit examples in four dimensions, incorporating and extending recent findings from cosmology-related literature associated with the concept of reframing.

ITMP seminar will be held on Wednesday, April 17 at 18:00. The seminar will be organized via zoom.

Presentation

### "Closed string origin of thermal entropy"

**Dr. Indranil Halder, Harvard University**

**April 10, 2024 (Wednesday)**

Abstract: $\alpha'$ corrections to near horizon dynamics of a Schwarzschild black hole in a large number of spacetime dimensions $D$ are governed by the worldsheet theory composed of the cigar CFT and the classical sigma model on the sphere at the horizon, along with a timelike-Liouville theory of central charge $26-D$. At leading order in weak string coupling, black hole thermodynamics is insensitive to the details of timelike Liouville theory. In this limit, we use the Lewkowycz-Maldacena-trick motivated infinitesimally off-shell closed string worldsheet formalism in [arxiv: 2310.02313] to calculate thermal entropy exactly in $\alpha'$. The leading term in the $\alpha'\to 0$ limit and the first stingy correction of our result are in precise agreement with the target space Callan-Myers-Perry formula.

ITMP seminar will be held on Wednesday, April 10 at 18:00. The seminar will be organized via zoom.

Presentation

### "Uniqueness of supersymmetric AdS_5 black holes"

**Dr. Sergei Ovchinnikov, ITMP MSU**

**April 3, 2024 (Wednesday)**

Abstract**:** The classification of anti de Sitter black holes is an open problem of central importance in holography. In this talk, I will present new advances in classification of supersymmetric solutions to five-dimensional gauged supergravity. In particular, we show that it is possible to show the uniqueness of known black hole solutions within a ‘Calabi-type’ subclass of solutions with biaxial symmetry. This subclass includes all currently known black hole solutions within this theory.

ITMP seminar will be held on Wednesday, April 3 at 19:00. The seminar will be organized via zoom.

Presentation

### "Supersymmetric CP^1 deformation and Conformal limits"

**Dr. Anton Pribytok, Steklov Mathematical Institute RAS & University of Padua**

**March 20, 2024 (Wednesday)**

Abstract: In the present work we prove that the supersymmetric deformation of the CP^1 sigma model, i.e. the supersymmetric generalization of the Fateev-Onofri-Zamolodchikov model, can be given in the form of generalised Gross-Neveu model. It appears natural to exploit this field-theoretic formalism to compute one- and two-loop beta-function. It is then establish that in the UV the theory flows to the super-Thirring model. We explicitly show that the last is equivalent to a sigma model with "cylinder" target space by computing correlators of primaries on both sides. Moreover, we also discover other conformal limits, which emerge from our superdeformed construction. A discussion on further extensions to Non-Kahler targets and relation with GSLM (mirror) theories will be provided.

ITMP seminar will be held on Wednesday, March 20 at 18:00. The seminar will be organized via zoom.

Presentation

### "Gravitational bound waveforms from amplitudes"

**Dr. Riccardo Gonzo, University of Edinburgh**

**March 13, 2024 (Wednesday)**

Abstract: We will develop a formalism to study the gravitational waveform emitted during the inspiral phase of the dynamics of compact objects (black holes, neutron starts) using the effective field theory approach with a point particle description. First, we will consider the scattering setup for the two-body problem where a natural on-shell relation between waveforms and amplitudes can be established in the classical limit. We will then derive a new surprising on-shell map between scattering and bound waveforms, which is inspired and confirmed by Post-Newtonian calculations with the standard time-domain multipoles, and we will show that a resummation of the perturbative series is required to make contact with phenomenological waveform models.

ITMP seminar will be held on Wednesday, March 13 at 18:00. The seminar will be organized via zoom.

### "Classical and quantum codes, 2d CFTs and holography"

**Prof. Anatoly Dymarsky, University of Kentucky**

**March 6, 2024 (Wednesday)**

Abstract: There is a rich connection between classical and quantum codes and holographic correspondence connecting 2d CFTs and abelian 3d Chern-Simons theories. In the 3d language the codes emerge as a way to parametrize condensable anyons. Upon condensation 3d topological field theory gives rise to 2d CFT at the boundary. This provides a way to construct 2d CFTs from codes - the so called "code CFTs". This construction has a natural interpretation in terms of a CSS quantum code (defined in terms of the original classical code, defining the CFT). From the holographic point of view a particularly interesting question is that of an ensemble of codes and associated code CFTs. The ensemble of boundary theories is holographically dual to "Chern-Simons gravity", a topological field theory that sums over 3d topologies.

ITMP seminar will be held on Wednesday, March 6 at 18:00. The seminar will be organized via zoom.

### "Higher spin symmetry/gravity and 3d bosonization duality"

**Dr. Evgeny Skvortsov, University of Mons **

**February 28, 2024 (Wednesday)**

Abstract: I discuss a rich class of 3d CFT’s - (Chern-Simons) vector models that were recently conjectured to exhibit a new duality - 3d bosonization duality. This duality can be explained as a consequence of a certain infinite-dimensional extension of conformal symmetry, known as slightly-broken higher spin symmetry. This is a new type of a physical symmetry and extends a Lie algebra to an L-infinity one. From the AdS/CFT vantage point, at least up to the 4-point functions the duality is also a consequence of existence of chiral higher spin gravity, which also implies the existence of new CFT’s that are closed hidden subsectors in Chern-Simons vector models.

ITMP seminar will be held on Wednesday, February 28 at 18:00. The seminar will be held at ITMP (room Г-725) with the possibility to join via Zoom.

### "High-Energy Behavior of Scattering Amplitudes in Theories with Purely Virtual Particles"

**Dr. Marco Piva, University of Warsaw**

**February 21, 2024 (Wednesday)**

Abstract: A certain class of renormalizable quantum field theories with purely virtual particles, including quantum gravity, exhibits undesired behaviors, typical of nonrenormalizable theories, and seems to violate unitarity bounds. In particular, cross sections can grow as powers of the center-of-mass energy squared. In this talk we argue that the problem should be viewed as a violation of perturbativity, instead of unitarity. Indeed, we show that nonperturbative techniques, such as resummation of self energies, fixes the issue. As an explicit example, we consider a class of O(N) theories, which can be studied exactly to the leading order in the large-N expansion. We show that, after the resummation, the cross sections correctly decrease as inverse powers of the center-of-mass energy squared and that the amplitudes satisfy unitarity. These results are compared to theories with ghosts, where the resummation does not help in improving the high-energy behavior, and to nonrenormalizable theories. Finally, the appearance of new resonances or bound states is discussed.

ITMP seminar will be held on Wednesday, February 21 at 18:00. The seminar will be organized via zoom.

### "Trace Anomalies, RG Flow and Scattering Amplitudes"

**Dr. Biswajit Sahoo, King's College London**

**February 14, 2024 (Wednesday)**

Abstract: I will describe how various vertices and scattering amplitudes, involving background fields, probe trace anomaly coefficients in a four-dimensional (4D) renormalization group (RG) flow. Specifically, I will explain how to couple dilaton and graviton fields to the degrees of freedom of 4D QFT, ensuring the conservation of the Weyl anomaly along the RG flow for the coupled system. By providing dynamics to the dilaton and graviton fields, I will demonstrate that the graviton-dilaton scattering amplitude receives a universal contribution, exhibiting helicity flipping and being proportional to (Δc−Δa) along any RG flow. Here, Δc and Δa represent the differences in the UV and IR CFT c- and a-trace anomalies, respectively. Using a dispersion relation, (Δc−Δa) can be related to spinning massive states in the spectrum of the QFT. We test our proposal through various perturbative examples. Finally, as an application of the proposal of probing the trace anomalies using scattering amplitude, we have derived a non-perturbative bound on the UV CFT a-anomaly coefficient using numerical S-matrix bootstrap program for massive RG flow.

ITMP seminar will be held on Wednesday, February 14 at 18:00. The seminar will be organized via zoom.

### "Shift Symmetries, Equivalence of EFTs and Time-Like Extra Dimensions"

**Prof. Kurt Hinterbichler, Case Western Reserve University**

**February 7, 2024 (Wednesday)**

Abstract: Poincare invariant effective field theories can have extended shift symmetries that indicate the spontaneous breaking of higher dimensional spacetime symmetries. Such theories are often the result of geometric actions describing the worldvolume dynamics of branes fluctuating in higher dimensions. I will review how these symmetries are classified and how the dynamics of the effective theories are expected to be determined solely by their degrees of freedom and symmetry breaking patterns. I will describe an example where a brane probing a spacelike extra dimension is equivalent to one probing a timelike extra dimension.

ITMP seminar will be held on Wednesday, February 7 at 18:00. The seminar will be organized via zoom.

### "Wilson Loops & Euclidean Wormholes"

**Dr. Panos Betzios, University of British Columbia**

**January 31, 2024 (Wednesday)**

Abstract: Euclidean wormholes are exotic types of gravitational solutions that still challenge our physical intuition and understanding. After reviewing universal properties of asymptotically AdS wormhole solutions from a gravitational (bulk) point of view and the paradoxes they raise, I will describe some concrete (microscopic) field theoretic setups and models that exhibit such properties. These models can be reduced to matrix integrals and crucially involve correlated ("entangled") sums of representations of the boundary symmetry group. Our focus will be the example of heavy correlated Wilson loops in N=4 SYM and related "bubbling wormhole" geometries in type IIB SUGRA.

ITMP seminar will be held on Wednesday, January 31 at 18:00. The seminar will be organized via zoom.

### "Conformal Renormalization of anti-de Sitter gravity"

**Prof. Rodrigo Olea, Universidad Andres Bello**

**December 13, 2023 (Wednesday)**

Abstract: Boundary counterterms are required to cancel the divergences in the bulk action of asymptotically AdS gravity. These boundary terms are prescribed by a systematic procedure known as Holographic Renormalization, developed in the context of AdS/CFT correspondence. In this seminar, we show that, in four and six bulk dimensions, these counterterms can also be obtained from a proper embedding of Einstein in Conformal gravity (Conformal Renormalization).

ITMP seminar will be held on Wednesday, December 13 at 18:00. The will be held at ITMP (room Г-725) with the possibility to join via Zoom.

** **

### "Duality-Invariant Non-linear Electrodynamics and Stress Tensor Flows"

**Dr. Christian Ferko, University of California, Davis**

**December 6, 2023 (Wednesday)**

Abstract: I will discuss recent work on the connection between duality-invariant theories of electrodynamics in four spacetime dimensions and deformations of the Lagrangian by functions of the energy-momentum tensor. Such deformations, which we refer to as "stress tensor flows", are inspired by Zamolodchikov's T \bar{T} deformation of two-dimensional quantum field theories. We find a surprising one-to-one correspondence between these ideas: every family of self-dual theories of electrodynamics (such as the Born-Infeld and Modified Maxwell theories) obeys a flow equation built from the energy-momentum tensor, and every stress tensor deformation gives rise to families of duality-invariant theories.

ITMP seminar will be held on Wednesday, December 6 at 18:00. The seminar will be organized via zoom.

** **

### "Scattering on effective strings and compactified membranes"

**Dr. Fiona Seibold, Imperial College London **

**November 29, 2023 (Wednesday)**

Abstract: The low-energy dynamics of confining strings is captured by the Nambu-Goto area action, which in critical dimension is related to an integrable TTbar deformation of a free theory. In this talk I will consider the setup of a membrane compactified on a circle, leading to a tower of massive modes. I will present the perturbative worldsheet S-matrix, compare with the Nambu-Goto case, and discuss the integrability of the model.

ITMP seminar will be held on Wednesday, November 29 at 18:00. The seminar will be organized via zoom.

### "Chiral phase transition in Gross-Neveu model"

**Prof. Konstantin Zarembo, Nordita & Niels Bohr Institute**

**November 22, 2023 (Wednesday)**

Abstract: In the Gross-Neveu model, just like in QCD, chiral symmetry is spontaneously broken in vacuum but can be restored at finite temperature and density. Mean-field theory (large-N) predicts a phase diagram remarkably similar to that of QCD with an emergent crystalline phase arising due to Peierls instability. Translations however cannot be broken in 1d due to Landau theorem. That calls for an exact solution not relying on the mean-field approximation. Since GN model is integrable one can exploit Bethe Ansatz to study its thermodynamics. I will discuss what the Bethe Ansatz predicts for the phase structure and excitation spectrum.

ITMP seminar will be held on Wednesday, November 22 at 18:00. The seminar will be organized via zoom.

Presentation

### "Large N Partition Functions, Holography, and Black Holes"

**Prof. Nikolay Bobev, KU Leuven **

**November 15, 2023 (Wednesday)**

Abstract: I will discuss the large N behavior of partition functions of the ABJM theory on compact Euclidean manifolds. I will pay particular attention to the S3 free energy and the topologically twisted index for which I will present closed form expressions valid to all orders in the large N expansion. These results have important implications for holography and the microscopic entropy counting of AdS_4 black holes which I will discuss. I will also briefly discuss generalizations of these results to the superconformal index, as well as to other 3d SCFTs arising from M2-branes. Finally, I will outline how this approach can be used to calculate thermal holographic observables beyond the leading order supergravity approximation.

ITMP seminar will be held on Wednesday, November 15 at 18:00. The seminar will be organized via zoom.

** **

### "Ghosts without runaway instabilities"

**Prof. Cedric Deffayet, Ecole Normale Superieure, LPENS**

**November 8, 2023 (Wednesday)**

Abstract: I discuss simple mechanical models with a ghost interacting with a positive energy degree of freedom, and yet, the phase-space motion can be shown analytically and numerically to be fully stable. This is based on e-prints 2305.09631 [gr-qc] and 2108-06296 [gr-qc].

ITMP seminar will be held on Wednesday, November 8 at 18:00. The seminar will be organized via zoom.

Presentation

### "New probes of the string spectrum"

**Dr. Chrysoula Markou, University of Mons**

**November 1, 2023 (Wednesday)**

Abstract: As is well known, the string spectrum comprises infinitely many states that can collectively be visualized along Regge trajectories of increasing mass and spin. Its massless and lightest levels, as well as certain higher spins including the leading Regge trajectory, have been the focus of past studies. In this talk, we will discuss new probes beyond the leading Regge, starting with the interactions of some of the lightest subleading massive spin-2 superstring states. We will then proceed to discuss a new way of organizing the string spectrum based on Howe duality, presented in recent work with Evgeny Skvortsov, which allows for a covariant method of excavating string states and their interactions by entire trajectories, rather than individually.

ITMP seminar will be held on Wednesday, November 1 at 18:00. The seminar will be organized via zoom.

**"**Stacking and balancing casual causality – Diagnosing (a)causality in the EFT of gravity**"**

**Calvin Chen, Imperial College London**

**October 25, 2023 (Wednesday)**

Abstract: In recent years, causality has emerged as a powerful criterion to distinguish between effective field theories (EFTs) arising from physical and unphysical high-energy theories. A direct way to ensure a given EFT is causal is to demand a lower bound on scattering time delays. In flat space, this is unambiguously dictated by the Minkowski light cones, but the situation is more subtle with dynamical gravity. I will make the case that the relevant notion is so-called infrared (IR) causality. As an example, I will apply this to study Gauss-Bonnet gravity in $D \geq 5$. Previously we found that, on spherically symmetric black hole backgrounds, potential signatures of IR causality violation are not large enough within the EFT of gravity to discard the Gauss-Bonnet operator. The parameter space allowed by IR causality is in fact consistent with gravitational positivity bounds. Attempts to bypass this conclusion use configurations of shockwaves designed to artificially enhance causality violation. In this talk I will emphasise that this is not possible. This talk is based on arXiv:2112.05031 and 2309.04534 in collaboration with C. de Rham, A. Margalit, and A. J. Tolley.

ITMP seminar will be held on Wednesday, October 25 at 18:00. The seminar will be organized via zoom.

** **

### "Bootstrapping the AdS Virasoro-Shapiro amplitude"

**Dr. Tobias Hansen, University of Oxford**

**October 11, 2023 (Wednesday)**

Abstract: I will present a constructive method to compute the Virasoro-Shapiro amplitude on AdS5xS5, order by order in AdS curvature corrections. A simple toy model for strings on AdS indicates that at order k the answer takes the form of a genus zero world-sheet integral involving single-valued multiple polylogarithms of weight 3k. The coefficients in an ansatz in terms of these functions are then fixed by Regge boundedness of the amplitude, which is imposed via a dispersion relation in the holographically dual CFT. We explicitly constructed the first two curvature corrections. Our final answer reproduces all CFT data available from integrability and all localisation results, to this order, and produces a wealth of new CFT data for planar N=4 SYM theory at strong coupling.

ITMP seminar will be held on Wednesday, October 11 at 18:00. The seminar will be organized via zoom.

** **

### "Trace anomaly in relativistic stars"

**Dr. Ignacio Reyes, University of Amsterdam**

**October 4, 2023 (Wednesday)**

Abstract: What are the essential aspects of quantum theory needed in order to understand compact relativistic objects? Relying solely on universal properties of QFTs at high energies, we show that as a star contracts towards its Buchdahl (rather than its Schwarzschild) radius, the effects of the trace anomaly become macroscopic at densities much below the Planck scale. The consequences of this may be observed, as we illustrate with minimally coupled scalar waves.

ITMP seminar will be held on Wednesday, October 4 at 18:00. The seminar will be organized via zoom.

### "Stability of nonsingular Cosmologies in Galileons with Torsion"

**Mauricio Valencia Villegas, ITMP MSU**

**September 27, 2023 (Wednesday)**

Abstract: Horndeski theory, also known as Galileons, is a modification of General Relativity by a scalar field, with higher derivatives in the action but with second order equations of motion. It has been widely studied in part due to the possibility to violate the null energy condition and to construct interesting cosmological solutions. In this talk we introduce Galileons on a spacetime with torsion and discuss the implications for the stability of the FLRW background against the graviton and the scalar mode. The main point is a critical modification of a well known No-Go theorem that holds for nonsingular cosmological solutions in the torsionless theory (up to some special cases). The talk is based on our recent studies: 2304.04722 and 2307.06929.

ITMP seminar will be held on Wednesday, September 27 at 18:00. The seminar will be organized in person in room г-725, ITMP with the possibility to join via zoom.

### "Zero charge and confinement in turbulence"

**Prof. Gregory Falkovich, Weizmann Institute of Science**

**September 20, 2023 (Wednesday)**

Abstract: I will describe an attempt to do renormalization in turbulence, considering waves that interact weakly via four-wave scattering (such as sea waves, plasma waves, spin waves, and many others). By summing the series of the most UV-divergent terms in the perturbation theory, we show that the true dimensionless coupling is different from the naive estimate, and find that the effective interaction either decays or grows explosively with the cascade extent, depending on the sign of the new coupling. The explosive growth possibly signals the appearance of a multi-wave bound state (solitons, shocks, cusps) similar to confinement in quantum chromodynamics.

ITMP seminar will be held on Wednesday, September 20 at 18:00. The seminar will be organized via zoom.

Presentation

### "Self-dual gravity and color/kinematics duality in AdS4"

**Dr. Arthur Lipstein, Durham University**

**June 7, 2023 (Wednesday)**

Abstract: Self-dual gravity has provided a very fruitful setting for studying the mathematical structure of perturbative quantum gravity in asympotically flat background. For example, in lightcone gauge it can be described by very simple scalar theory which make various properties such as color/kinematics duality and the double copy manifest. In this talk I will describe how to generalise this description to AdS4 background. This implies an AdS4 version of the so-called kinematic algebra which can be lifted to a deformed version of the w_{infinity} algebra, which plays a prominent role in celestial holography.

ITMP seminar will be held on Wednesday, June 7 at 18:00. The seminar will be organized via zoom.

### "The role of symmetry for finding black holes in scalar tensor theories"

**Prof. Mokhtar Hassaine, University of Talca**

**May 31, 2023 (Wednesday)**

Abstract: In dimension 4, we will consider Horndeski's theory which is the most general (single) scalar-tensor theory with second order equations of motion. We will see how certain symmetries for these theories can be useful in determining explicit black hole-like solutions for these theories. In particular we will see how the conformal invariance of the matter action or only the conformal invariance of the equation of the scalar field can turn out to be of great use to go beyond the no-go theorems and to construct explicit black hole type solutions. We will also present the most general action in four dimensions that gives rise to a second-order conformal scalar field equation.

ITMP seminar will be held on Wednesday, May 31 at 18:00. The seminar will be organized via zoom.

### "The String Axiverse in 2023"

**Dr. David Marsh, King's College London**

**May 24, 2023 (Wednesday)**

Abstract: In 2009 the highly influential idea of a "string axiverse" was proposed, which has dominated my own research. This talk attempts to review the progress myself and others have made on this idea in the last 14 years. The original probes proposed: matter power spectrum, birefringence, superradiance, and axion decays have all matured in precision both theoretically and observationally, which I will describe, along with other related probes, in particular in cosmology. I will then describe recent dramatic progress that has been made in constructing explicit axiverses from Calabi-Yau compactifications across the entire "Kreuzer-Skarke" database in Type IIB string theory, and the similarities and differences between such axiverses and the conjectures in 2009. Superradiance has already been used to constrain the resulting landscape in a narrow search. I will end by outlining some dreams for the future of this program.

ITMP seminar will be held on Wednesday, May 24 at 18:00. The seminar will be organized via zoom.

### "Chaos and the reparametrization mode on the AdS_2 String"

**Bendeguz Offertaler, Princeton University**

**May 10, 2023 (Wednesday)**

Abstract: Out-of-time-order correlators (OTOCs) are a simple diagnostic of quantum chaos. It is known that the four-point OTOC of fluctuations on the fundamental string in AdS displays Lyapunov growth at early times with the Lyapunov exponent saturating the chaos bound. This talk, based on https://arxiv.org/abs/2212.14842 in collaboration with S. Giombi and S. Komatsu, will focus on the string OTOC in a double scaling limit that interpolates between the Lyapunov regime at early times and exponential decay at late times. The double scaled OTOC can be obtained exactly and takes the same functional form as the OTOC in JT gravity. After first reviewing the Wilson loops / strings duality in AdS/CFT and the set-up of our analysis, I will discuss how the double scaled OTOC can be understood in terms of a high energy scattering process on the string worldsheet, with the scattering interaction governed by the worldsheet S-matrix of the long string in flat space. A complementary approach is to study the fluctuations of the string in conformal gauge, in which a key role is played by the dynamical reparametrization mode on the boundary, which is governed by a non-local effective action. The OTOC in the double scaling limit can be obtained from the reparametrization action by resumming a subset of diagrams expected to dominate in the limit. In this approach, the reparametrization action on the AdS_2 string plays an analogous role to the Schwarzian action in JT gravity.

ITMP seminar will be held on Wednesday, May 10 at 18:00. The seminar will be organized via zoom.

### "A New Gravitational Action for the Trace Anomaly"

**Prof. Gregory Gabadadze, New York University**

**May 3, 2023 (Wednesday)**

Abstract: General Relativity (GR) combined with the existing action for the trace anomaly is an inconsistent low energy effective field theory. This issue is addressed by extending GR into a certain scalar-tensor theory, which preserves the GR trace anomaly equation, up to higher order corrections. The extension introduces a new mass scale — assumed to be below the Planck scale — that governs four high dimensional terms in a local diff-invariant trace anomaly action. Such terms can be kept, while an infinite number of Planck-suppressed invariants are neglected. The resulting theory maintains two derivative equations of motion. In a certain approximation it reduces to the conformal Galileon, which could have physical consequences.

ITMP seminar will be held on Wednesday, May 3 at 18:00. The seminar will be organized via zoom.

### "Can dilaton be QCD axion?"

**Dr. Anna Tokareva, Imperial College London**

**April 19, 2023 (Wednesday)**

Abstract: The Standard Model Lagrangian has an approximate scale symmetry in the high-energy limit. This observation can be embedded into the fundamental principle of the ultimate theory of Nature as the requirement of the exact quantum scale invariance. In this setup, all low-energy particle phenomenology can be obtained as a result of the spontaneous breaking of scale symmetry leading to the presence of the extra massless scalar field — the dilaton. I explore the scenario, in which this field is also capable of solving the strong CP-problem in QCD in a similar way as in QCD axion models. The dilaton, playing the role of the axion, is coupled to the QCD sector and acquires a mass term due to non-perturbative breaking of scale symmetry. I show that the dilaton can form dark matter after the low-scale inflation. As a proof of concept, I present a model of Higgs-driven inflation consistently realising the axion-like dilaton dark matter production compatible with the CMB data.

ITMP seminar will be held on Wednesday, April 19 at 18:00. The seminar will be organized via zoom.

### "Classical Vs Quantum gravity: gravity induced entanglement revisited"

**Prof. Eduardo Martin-Martinez, University of Waterloo**

**April 12, 2023 (Wednesday)**

Abstract: We will discuss the differences and similarities between a classical (but relativistic and local) field theory and a relativistic quantum field theory. We will identify regimes where a quantum field theoretical description is not necessary to explain phenomenology of matter that interacts through fields. We will then apply what we learned to the study of gravity induced entanglement experiments to venture how much their experimental realization can actually say about quantum gravity.

ITMP seminar will be held on Wednesday, April 12 at 18:00. The seminar will be organized via zoom.

### "Black holes and vacuum decay"

**Dr. Andrey Shkerin, University of Minnesota, FTPI**

**April 5, 2023 (Wednesday)**

Abstract: We will discuss the decay of a metastable vacuum catalysed by black holes. The phenomenological interest in this problem lies in the fact that our current electroweak vacuum may not be absolutely stable. Its lifetime, while sufficiently large in the present-day Universe, may be significantly reduced in extreme environments such as the vicinity of small hot primordial black holes, which could be produced abundantly in the early Universe. From the theoretical point of view, the challenge is to compute the rate of decay of the false quantum vacuum state which lives in a curved spacetime and which is generally out of thermal equilibrium. I will discuss a general method of doing so and illustrate it using toy models of dilaton black holes in two dimensions. We will see that different vacuum states associated with a black hole have parametrically different lifetimes. Hence, in computing the enhancement of the electroweak vacuum decay rate near black holes it is important to choose the physically relevant (Unruh) vacuum state. Finally, I will outline what remains to be done in the realistic case of black holes in four dimensions.

ITMP seminar will be held on Wednesday, April 5 at 18:00. The seminar will be organized via zoom.

### "Multiparticle production in λϕ^4 theory: method of singular solutions and numerical results"

**Bulat Farkhtdinov, INR RAS & MIPT, Moscow**

**March 29, 2023 (Wednesday)**

Abstract: We consider the creation of n>>1 scalar bosons from several colliding ones in the (3+1)-dimensional λϕ^4 theory without spontaneous symmetry breaking. When coupling λ is weak, probabilities of these processes can be calculated using the semiclassical method of singular solutions. We numerically implemented this method and for the first time obtained reliable results for probabilities in the region of an exceptionally large number of particles in the final state λn>>1, where probabilities decrease exponentially with growth of n. The exponent depends linearly on n, and its slope depends on the average kinetic energy ε of the created particles. In the opposite limit of λn<<1, our numerical data agree with the known tree-level results, and data in the region λn~1 interpolate between these two limits. Overall, this proves exponential suppression of the multiparticle production probability at n≫1 and arbitrary ε in the unbroken theory. In the talk I will cover both the method of singular solutions itself, its numerical implementation, and the obtained results.

ITMP seminar will be held on Wednesday, March 29 at 18:00. The seminar will be organized via zoom.

### "Deterministic chaos and Integrable Systems"

**Dr. Stefano Negro, New York University**

**March 22, 2023 (Wednesday)**

Abstract: Integrability and chaos are commonly assumed to be incompatible concepts. There are important reasons for this. Prime amongst these is that integrable systems are not expected to thermalise since their phase space is entirely foliated by invariant tori thanks to the presence of a large amount of symmetries. On the other hand, a deep relation exists between thermalisation and chaotic behaviour, so much so that these concepts are commonly conflated. In this talk, starting from a definition of chaos as the property of the dynamics to map small intervals to unboundedly large ones, I will present some evidence that certain integrable systems, notably integrable field theories, present this behaviour. These results suggest the need for a more careful and deep understanding of the relationship between the concepts of chaos, thermalisation and integrability, in particular when the dimension of the systems’ phase spaces is infinite.

ITMP seminar will be held on Wednesday, March 22 at 18:00. The seminar will be organized via zoom.

### "Unifying Constructions of Non-Invertible Symmetries"

**Dr. Lakshya Bhardwaj, University of Oxford**

**March 15, 2023 (Wednesday)**

Abstract: I will describe a unified perspective on various constructions of non-invertible symmetries, using the so-called theta defects. The study of theta defects is intricately tied to the study of equivariant TQFTs in mathematical physics, the study of symmetry protected topological phases of matter in condensed matter physics, and the study of higher-representations of groups and higher-groups in mathematics.

ITMP seminar will be held on Wednesday, March 15 at 18:00. The seminar will be organized via zoom.

### "On the chaotic aspects of highly excited string amplitudes"

**Dr. Maurizio Firrotta, University of Rome Tor Vergata**

**March 1, 2023 (Wednesday)**

Abstract: I will discuss some novel aspects related to the chaotic behaviour of highly excited string scattering amplitudes. In particular I will review the DDF construction of HES states and I will discuss the connection between chaos and thermal effects that emerges in the general decay of HES states. Finally I will discuss the possibility of exploring the size and the shape of arbitrarily excited string states.

ITMP seminar will be held on Wednesday, March 1 at 18:00. The seminar will be organized via zoom.

** **

### "QFT in AdS instead of LSZ"

**Xiang Zhao, EPFL Lausanne, FSL**

**February 22, 2023 (Wednesday)**

Abstract: Quantum ﬁeld theories in AdS generate conformal correlation functions on the boundary, and in the limit where AdS is nearly ﬂat one should be able to extract an S-matrix from such correlators. In this talk I will discuss a particularly simple position-space procedure to do so. In the first half I will state the prescription, motivate it through perturbative examples and discuss some of its subtleties. In the second half, I will move on to non-perturbative establishment of the flat-space limit prescription. With minimal assumptions I will show that the resulting S-matrix element from the flat-space limit obeys a dispersion relation and the non-linear unitarity conditions.

ITMP seminar will be held on Wednesday, February 22 at 18:00. The seminar will be organized via zoom.

### "Finite Features in Holography"

**Dr. Dionysios Anninos, King’s College London**

**December 14, 2022 (Wednesday)**

Abstract: We consider theories of gravity where a more "finite" holographic theory is relevant. From a Lorentzian perspective we comment on properties of gravity in the presence of finite timelike boundaries, and holographic realisations. Time permitting, we also discuss Euclidean gravity on manifolds with no boundary, like Euclidean de Sitter.

ITMP seminar will be held on Wednesday, December 14 at 18:00. The seminar will be organized via zoom.

### "Automorphic symmetry and AdS String novel integrable deformations"

**Anton Pribytok, Trinity College, Dublin**

**December 7, 2022 (Wednesday)**

Abstract: We address the new structures arising in quantum and string integrable theories, as well as construct a method to find them. Initially we implement the automorphic symmetries on periodic lattice systems and exploit properties of an integrable hierarchy. This prescription is first applied for potentially new sl_2 sector, Generalised Hubbard type classes and more. We then construct a boost recursion for systems with R-/S-matrices that exhibit arbitrary spectral dependence, which is also an apparent property of the scattering in AdS integrable backgrounds. The generalised bottom-up approach based on coupled differential systems is derived to resolve for R-matrices exactly. In addition, one can isolate a special class of models (non-difference form) that provide a new structure consistently arising in AdS_{3} and AdS_{2} string backgrounds. These classes can be proven to be represented as deformations of the AdS_{2,3} models, which satisfy free fermion, constraint, braiding unitarity, crossing and exhibit deformed algebraic structure that shares certain properties with AdS_3xSˆ3xMˆ4 and AdS_2xSˆ2xTˆ6 models. A related discussion on further investigation of AdS_3 free fermion property, TBA finite size corrections and GSE will be provided.

ITMP seminar will be held on Wednesday, December 7 at 18:00. The seminar will be organized via zoom.

** **

### "Angular Momentum Loss Due to Tidal Effects in the Post-Minkowskian Expansion"

**Dr. Carlo Heissenberg, Uppsala University and NORDITA**

**November 30, 2022 (Wednesday)**

Abstract: The steadily increasing sensitivity of gravitational-wave measurements challenges the state of the art of precision calculations for gravitational collisions. In this context, scattering amplitudes have contributed to the advance of the precision frontier in the Post-Minkowskian (PM) expansion, based on successive approximations labeled by powers of Newton's constant G and valid for generic velocities. In this talk, based on arXiv:2210.15689, I will illustrate the calculation of tidal corrections to the loss of angular momentum in a two-body collision at leading Post-Minkowskian order from an amplitude-based approach. The eikonal operator allows us to efficiently combine elastic and inelastic amplitudes, and captures both the contributions due to genuine gravitational-wave emissions and those due to the static gravitational field. We calculate the former by harnessing powerful collider-physics techniques such as reverse unitarity, thereby reducing them to cut two-loop integrals. For the latter, we can employ the results of arXiv:2203.11915 where static-field effects were calculated for generic gravitational scattering events using the leading soft graviton theorem.

ITMP seminar will be held on Wednesday, November 30 at 18:00. The seminar will be organized via zoom.

**"AdS/BCFT from Bootstrap: Construction of Gravity with particle & brane"**

**Dr. Yuya Kusuki, Caltech and Wako, RIKEN**

**November 23, 2022 (Wednesday)**

Abstract: We consider gravity with branes and massive particles, which has many unclear aspects. For example, we do not know how to understand some problematic configurations, like brane self-intersections, negative tension branes, and spinning particles interacting with branes. We address these issues through AdS/BCFT. We solve a related conformal bootstrap and show that the self-intersection can be avoided by the black hole formation. We also reveal how to resolve the other problems in AdS/BCFT using the bootstrap.

In the later part, we give the resolution of the same problems from the gravity side. For this purpose, we develop a simple way to construct gravity with branes and particles by cutting and pasting. The solution from this construction tells us how to resolve the issues from the gravity side, which is completely consistent with the CFT result.

As a bonus, we find a refined formula for the holographic Rényi entropy, which appears to be crucial to correctly reproduce the boundary entropy term. We also find a holographic dual of boundary primaries.

ITMP seminar will be held on Wednesday, November 23 at 18:00. The seminar will be organized via zoom.

### "R-matrix formulation of affine Yangian of \hat{gl}(1|1) and integrable systems of N=2 superconformal field theory"

**Dr. Alexey Litvinov, Landau ITP, Chernogolovka**

**November 16, 2022 (Wednesday)**

Abstract: We study N=2 superconformal field theory and define the R-matrix which acts as an intertwining operator between different realisations of N=2W -algebras of type A. Using the R-matrix we define RLL algebra and relate it to current realisation of affine Yangian of \hat{gl}(1|1). We also derive Bethe ansatz equations for the spectrum of integrals of motion.

ITMP seminar will be held on Wednesday, November 9 at 18:00. The seminar will be organized in person in room г-725, ITMP with the possibility to join via zoom.

### "Intersecting D-brane models and the anomalous magnetic moment of the muon"

**Francois Rondeau, Cyprus University**

**November 9, 2022 (Wednesday)**

Abstract: The anomalous magnetic moment of the muon ($(g-2)_{\mu}$) might be one of the most promising signals of new physics beyond the Standard Model (SM). The theoretical calculation predicts a value smaller than the experimental measurement from the Brookhaven National Laboratory and Fermilab experiments, with a standard deviation of $4.7\sigma$. This talk will discuss recently proposed solutions to this discrepancy in the framework of low mass scale strings, large extra dimensions and intersecting D-brane physics.

After reminding some basic aspects of intersecting D-brane models, and in particular how the SM of particle physics can be obtained in this framework, we will present two proposals able to explain (part of) the observed discrepancy. They are based on the contributions to the $(g-2)_{\mu}$ coming from the Kaluza-Klein (KK) states of the lepton number gauge boson, corresponding to an open string tied to a leptonic $U(1)$ brane, as well as from light scalars corresponding to the first stringy excitations of an open string stretched between two D-branes intersecting with an ultra-small angle. In both cases, we show that there is a region of the parameter space compatible with the current experimental bounds, where these states can provide significant contributions to the $(g-2)_{\mu}$, and fully or partially bridge the gap in the observed discrepancy. We then build the minimal D-brane configurations able to realise these two proposals.

The talk is based on 2110.01247, 2112.07587 and 2209.11152.

ITMP seminar will be held on Wednesday, November 9 at 18:00. The seminar will be organized via zoom.

### "Chiral Approach to Massive Higher Spins"

**Dr. Alexander Ochirov, London Institute for Mathematical Sciences**

**November 2, 2022 (Wednesday)**

Abstract: Quantum field theory of higher-spin particles is a formidable subject, where preserving the physical number of degrees of freedom in the Lorentz-invariant way requires a host of auxiliary fields. They can be chosen to have a rich gauge-symmetry structure, but introducing consistent interactions in such approaches is still a non-trivial task, with massive higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with the unphysical degrees of freedom. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistently interacting field theories with massive higher-spin fields.

ITMP seminar will be held on Wednesday, November 2 at 18:00. The seminar will be organized via zoom.

### "Exact off-shell Sudakov form factor in N=4 SYM"

**Dr. Leonid Bork, ITEP, Moscow**

**October 26, 2022 (Wednesday)**

Abstract: We consider the Sudakov form factor in N=4 SYM in the off-shell kinematical regime, which can be achieved by considering the theory on its Coulomb branch. We demonstrate that up two three loops both the infrared-divergent as well as the finite terms do exponentiate, with the coefficient accompanying log’s of mass determined by the octagon anomalous dimension Γ_oct. This behaviour is in strike contrast to previous conjectural accounts in the literature. Together with the finite terms we observe that up to three loops the logarithm of the Sudakov form factor is identical to twice the logarithm of the null octagon O_0, which was recently introduced within the context of integrability-based approaches to four point correlation functions with infinitely-large R-charges. The null octagon O_0 is known in a closed form for all values of the 't Hooft coupling constant and kinematical parameters. We conjecture that the relation between O_0 and the off-shell Sudakov form factor will hold to all loop orders.

ITMP seminar will be held on Wednesday, October 26 at 18:00. The seminar will be organized in person in room г-725, ITMP with the possibility to join via zoom.

### "Phase transitions in the dark Universe"

**Dr. Sabir Ramazanov, CEICO, Prague**

**October 19, 2022 (Wednesday)**

Abstract: Typically phase transitions are associated with a constant scale of symmetry breaking. In cosmology, however, a different situation is also natural: the expectation value of a scalar field responsible for symmetry breaking can be induced by its interactions with hot primordial plasma, in which case the expectation value decreases as the Universe cools down. This picture can be realized in a simple renormalizable and approximately scale-invariant scenario. Non-trivial time-dependence of the symmetry breaking scale enables new mechanisms of particle production at phase transitions. These particles can be considered for the role of dark matter. Another phenomenologically interesting outcome of phase transitions is formation of topological defects, which serve as a source of potentially observable gravitational waves. The latter can be used to probe the underlying model in a very weakly coupled regime inaccessible by other experiments.

ITMP seminar will be held on Wednesday, October 19 at 18:00. The seminar will be arranged via Zoom.

** **

### "An Effective Field Theory for Large Oscillons"

**Vasily Maslov, ITMP**

**October 5, 2022 (Wednesday)**

Abstract: Based on arXiv:2208.04334. We consider oscillons - localized, quasiperiodic, and extremely long-living classical solutions in models with real scalar fields. We develop their effective description in the limit of large size at finite field strength. Namely, we note that nonlinear long-range field configurations can be described by an effective complex field $\psi(t, \mathbf{x})$ which is related to the original fields by a canonical transformation. The action for $\psi$ has the form of a systematic gradient expansion. At every order of the expansion, such an effective theory has a global U(1) symmetry and hence a family of stationary nontopological solitons - oscillons. The decay of the latter objects is a nonperturbative process from the viewpoint of the effective theory. Our approach gives an intuitive understanding of oscillons in full nonlinearity and explains their longevity. Importantly, it also provides reliable selection criteria for models with long-lived oscillons. This technique is more precise in the nonrelativistic limit, in the notable cases of nonlinear, extremely long-lived, and large objects, and also in lower spatial dimensions. We test the effective theory by performing explicit numerical simulations of a (d+1)-dimensional scalar field with a plateau potential.

ITMP seminar will be held on Wednesday, October 5 at 18:00. The seminar will be arranged via Zoom.

### "Recent developments in higher spin gravity"

**Dr. Evgeny Skvortsov, University of Mons**

**September 28, 2022 (Wednesday)**

Abstract: Firstly, I will review main ideas behind higher spin gravity and well-known obstructions to constructing such theories in flat and anti-de Sitter spaces. I will give a short list of theories that avoid these no-go's. In the main part, I will present in detail Chiral higher spin gravity, which is the only consistent model with propagating massless fields at present: action, quantum checks, consistent truncations, applications to AdS/CFT and 3d bosonization duality. If time permits, I will discuss appications of higher spin symmetries to 3d bosonization.

ITMP seminar will be held on Wednesday, September 28 at 18:00. The seminar will be arranged via Zoom.

### "Colorful particles and fields in low dimensions"

**Dr. Euihun Joung, Kyung Hee University, Seoul**

**June 8, 2022 (Wednesday)**

Abstract: I will present a few recent applications of colorful extensions of spacetime symmetries to the theories of particles and fields in two and three dimensions. In particular, the two dimensional BF theories is shown to reduce a colorful extension of Schwarzian theory.

ITMP seminar will be held on Wednesday, June 8 at 18:00. The seminar will be arranged via Zoom.

** **

### "Invariant traces of the flat space chiral higher-spin algebra as scattering amplitudes"

**Dr. Dmitry Ponomarev, ITMP MSU**

**June 1, 2022 (Wednesday)**

Abstract: We sum up two- and three-point amplitudes in the chiral higher-spin theory over helicities and find that these quite manifestly have the form of invariant traces of the flat space chiral higher-spin algebra. We consider invariant traces of products of higher numbers of on-shell higher-spin fields and interpret these as higher-point scattering amplitudes. This construction closely mimics its anti-de Sitter space counterpart, which was considered some time ago and was confirmed holographically.

ITMP seminar will be held on Wednesday, June 1 at 18:30. The seminar will be arranged via Zoom.

### "q-Virasoro constraints and the algebra of Wilson loops in 3d"

**Dr. Luca Cassia, Uppsala University**

**May 25, 2022 (Wednesday)**

Abstract: The BPS/CFT correspondence predicts that the partition function and other BPS observables in a 3d N=2 gauge theory can be mapped to states in a q-deformed CFT, i.e. a theory whose symmetry algebra is q-Virasoro. Following this idea, I will discuss how to derive q-Virasoro constraints for the generating function of 1/2-BPS Wilson loops for a family of 3d N=2 gauge theories. Under certain assumptions on the Chern--Simons level and the number of flavors the constraints can be solved exactly and the solution can be recast as a "superintegrability" formula for characters of the gauge group. Moreover, I will show that the same logic can be applied to refined Chern--Simons theories and refined ABJ theories to derive formulas for refined knot invariants of the unknot. If time permits I will also discuss the symmetries of the constraints and their physical interpretation as dualities of the gauge theory. The talk is based on https://arxiv.org/abs/2007.10354 and https://arxiv.org/abs/2107.07525.

ITMP seminar will be held on Wednesday, May 25 at 18:00. The seminar will be arranged via Zoom.

** **

### "Null Wilson loop with Lagrangian insertion in N=4 super Yang-Mills theory"

**Dr. Dmitry Chicherin, Annecy LAPTH**

**May 18, 2022 (Wednesday)**

Abstract: Null Wilson loops in N = 4 super Yang-Mills are dual to planar scattering amplitudes. The duality holds at the level of their finite four-dimensional loop integrands as well as for the integrated observables with properly regularized infrared and cusp divergences. We consider a closely related infrared-finite four-dimensional observable which interpolates between the integrand and the fully loop-integrated quantity. It is defined as the null polygonal Wilson loop with a Lagrangian insertion normalized by the Wilson loop without insertion. Unlike the ratio and remainder functions of N = 4 super Yang-Mills amplitudes, this observable is non-trivial already at four points and it is reminiscent of finite parts of QCD amplitudes. We discuss the general structure of this n-point observable at weak coupling. At n>4, the loop corrections have rich kinematics. Indeed, there are several leading singularities and the accompanying loop functions are multivariable transcendental functions. We discuss a Grassmannian representation for the leading singularities and reveal their conformal and dual conformal symmetries. We conjecture a duality relation between the observable and the highest transcendentality piece of the planar all-plus amplitude in pure Yang-Mills theory. We test the duality using the one-loop n-point and two-loop four-point perturbative data for the observable. Relying on the duality, we predict the highest weight piece of the three-loop five-particle all-plus amplitude.

ITMP seminar will be held on Wednesday, May 18 at 18:00. The seminar will be arranged via Zoom.

** **

### "Quantum states and their back-reacted geometries"

**Prof. Sergey Solodukhin, University of Tours**

**May 11, 2022 (Wednesday)**

A black hole quantum state (Hartle-Hawking or Boulware) is usually defined in a fixed background of a classical black hole. In my talk I will discuss the corresponding space-time geometry when the back-reaction is taken into account. The important questions include: does the back-reacted geometry always contain a horizon?; how it depends on the choice of the quantum state?; and what is the right choice for the quantum state for the non-physical fields such as ghosts? I will answer these and other questions in the context of a two-dimensional dilaton gravity. The talk is based on a joint recent work with D. Sarkar and Y. Potaux, arXiv:2112.03855.

ITMP seminar will be held on Wednesday, May 11 at 18:00. The seminar will be arranged via Zoom.

** **

### "How Pauli-Villars’ regularization tells the Nambu-Goto and Polyakov strings apart"

**Dr. Makeenko Yuri M, ITEP Moscow**

**April 27, 2022 (Wednesday)**

Abstract: It is known since 1980s that both lattice regularizations and the KPZ-DDK technique work for bosonic strings only in target-space dimension d<2. I discuss first that the classical string ground state is unstable for d>2, where another quantum ground state has lower energy and is stable under fluctuations for d<26. Then I consider high-derivative corrections to the Liouville action emerging from higher orders of the Seeley expansion and show at one loop that the KPZ-DDK technique tells the Nambu-Goto and Polyakov strings apart.

ITMP seminar will be held on Wednesday, April 27 at 18:00. The seminar will be arranged via Zoom.

### "Recursion Relations for Five-Point Conformal Blocks and Beyond: A Practical Approach"

**Dr. Valentina Prilepina, ITMP**

**April 20, 2022 (Wednesday)**

Abstract: In this talk, I will consider five-point functions in conformal field theories (CFTs) in d > 2 spacetime dimensions. I will put forward a concrete and practical approach to computing global conformal blocks that appear in five-point functions of arbitrary scalar operators in general CFTs. By exploiting the weight-shifting operator formalism, I will construct a simple set of recursion relations for generating five-point blocks for arbitrary symmetric traceless exchange, which may be utilized to reduce such blocks to linear combinations of scalar exchange blocks with shifted external dimensions. Throughout, I will restrict attention to parity-even five-point functions in parity-preserving CFTs. Our results may be seen as a natural generalization of the work of Dolan and Osborn to the 5-point case. Moving beyond the external scalar case, I will consider how to promote one of the external scalars to a spin-1 or a spin-2 operator. I will show a way to derive additional recursion relations which encode these blocks in terms of combinations of weight shifting operators acting on the seed blocks for external scalars. I will comment on one possible application of these results. Lastly, I will reach beyond five-point functions to describe some ongoing work on generalizations of such techniques to six-point functions. I will also comment on our current attempts to bootstrap the 3D Ising model via five-point blocks.

ITMP seminar will be held on Wednesday, April 20 at 18:00. The seminar will be arranged via Zoom.

### "Exact quantization"

**Barak Gabai, Harvard University**

**April 13, 2022 (Wednesday)**

Abstract: 1d Hamiltonian problems are classically-integrable by definition. A manifestation of that is the fact that we can always use action-angle coordinates to parametrize the phase space. A generalization of the action variables to QM is not immediately obvious. In the presentation I will explain how to define rigorous quantities that can be thought of as the quantum action variables and how to write down an integral equation that determines their values, for a large class of 1d Schrodinger problems. Then, I will argue that these objects encode all of the dynamical information about the Quantum system, and explain how to extract the spectrum. The results are exact and rigorous.

ITMP seminar will be held on Wednesday, April 13 at 18:00. The seminar will be arranged via Zoom.

** **

### "Anomaly-free scale symmetry and gravity"

**Prof. Mikhail Shaposhnikov, EPFL Lausanne**

**April 6, 2022 (Wednesday)**

Abstract: What is the global symmetry of Nature? In the absence of gravity, the most obvious answer to this question is given by special relativity and is associated with the Poincare transformations. As was noted a long time ago, the free Maxwell equations have a wider symmetry group - the 15 parameters conformal invariance, containing in addition to ten Poincare generators, four special conformal transformations, and dilatations. Dilatations change the length of the rulers, while special conformal transformation can bend the lines but do not alter the angles between them. Could it be that the symmetry of all interactions is conformal? We show that conformal symmetry can be made free from the quantum anomaly only in the flat space. The presence of gravity would reduce the global symmetry group of the fundamental theory to the scale invariance only. We discuss how the effective Lagrangian respecting the scale symmetry can be used for the description of particle phenomenology and cosmology.

ITMP seminar will be held on Wednesday, April 6 at 18:00. The seminar will be arranged via Zoom.

### "Graviton Scattering in AdS at Two Loops"

**Dr. Ellis Ye Yuan, Zhejiang University**

**March 30, 2022 (Wednesday)**

Abstract: I will present a preliminary result on the third-order correction in 1/N expansion to the four-point correlator of the stress tensor multiplet in N=4 super Yang-Mills theory at large 't Hooft coupling, which corresponds to the two-loop scattering of four gravitons in the dual AdS5×S5 supergravity. This is obtained by bootstrapping an educated ansatz based on intuitions from a hidden 10-dimensionthe conformal symmetry, which I will describe in detail.

ITMP seminar will be held on Wednesday, March 30 at 18:00. The seminar will be arranged via Zoom.

### "On moduli stabilisation, de Sitter spacetime and inflation from string compactifications"

**Prof. Fernando Quevedo, Cambridge University**

**March 23, 2022 (Wednesday)**

Abstract: An overview of the different attempts to stabilise the moduli fields, measuring the size and shape of the extra dimensions in string theory, will be given. The extension of these techniques towards obtaining de Sitter spacetime and a period of early universe inflation will be highlighted, emphasizing recent progress and open challenges.

ITMP seminar will be held on Wednesday, March 23 at 18:00. The seminar will be arranged via Zoom.

### "On AdS3 Holography"

**Jan Troost, Ecole Normale Supérieure, Paris**

**March 16, 2022 (Wednesday)**

Abstract: I will provide a conceptual tour of our recent work on holography in asymptotically AdS3 space-times. I will discuss a proposed conformal field theory dual of pure AdS3 gravity, how to implement topological twisting in quantum theories of supergravity and I will touch upon the determination of the energy of asymptotic winding strings in black holes in AdS3 space-time.

ITMP seminar will be held on Wednesday, March 16 at 18:00. The seminar will be arranged via Zoom.

### "Quantum Gravity on a Manifold with boundaries: Schrödinger Evolution and Constraints"

**Dr. Jose Alejandro Rosabal, ITMP MSU**

**March 9, 2022 (Wednesday)**

Abstract: In this work, we derive the boundary Schr¨odinger (functional) equation for the wave function of a quantum gravity system on a manifold with boundaries. From a detailed analysis of the gravity boundary condition on the spatial boundary, we find that while the lapse and the shift functions are independent Lagrange multipliers on the bulk, on the spatial boundary, these two are related; namely, they are not independent. In the Hamiltonian ADM formalism, a new Lagrange multiplier, solving the boundary conditions involving the lapse and the shift functions evaluated on the spatial boundary, is introduced. The classical equation of motion associated with this Lagrange multiplier turns out to be an identity when evaluated on a classical solution of Einstein’s equations. On the other hand, the quantum counterpart is a constraint equation involving the gravitational degrees of freedom defined only on the boundary. This constraint has not been taken into account before when studying the quantum gravity Schr¨odinger evolution on manifolds with boundaries.

ITMP seminar will be held on Wednesday, March 9 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Horava gravity as palladium of locality, unitarity and renormalizability: methods and results"

**Dr. Andrei O. Barvinsky, Lebedev Institute, ITMP**

**March 2, 2022 (Wednesday)**

Abstract: We discuss problems of covariant renormalization of Lorentz non-invariant Horava gravity models. Projectable version of these models in generic spacetime dimensions is shown to maintain UV renormalizability, locality and unitarity, which is based on the BRST structure of renormalization in a special class of regular background covariant gauges. Renormalization group flow with the asymptotically free UV fixed point is presented in (2+1)-dimensional theory. Beta functions of (3+1)-dimensional theory are obtained by the combination of dimensional reduction and the method of universal functional traces. They feature fixed points with several candidates for asymptotic freedom and also suggest an intriguing connection between the (3+1)-dimensional Horava gravity with detailed balance and gravitational Chern-Simons/topological massive gravity.

ITMP seminar will be held on Wednesday, March 2 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

** **

### "An Overview of Quadratic Gravity"

**Prof. John F. Donoghue, University of Massachusetts**

**February 16, 2022 (Wednesday)**

Abstract: Quadratic Gravity is a renormalizeable UV completion of quantum gravity which retains the metric as the fundamental field. However, it appears that it must violate at least one property which we normally expect for our quantum field theories. I will give an overview of work analyzing the theory, and of the remaining unknown aspects of its QFT treatment.

ITMP seminar will be held on Wednesday, February 16 at 18:00. The seminar will be arranged via Zoom.

### "$J\bar T$ - deformed CFTs as non-local CFTs"

**Dr. Monica Guica, Institute of Theoretical Physics, Saclay**

**January 26, 2022 (Wednesday)**

Abstract: I will start with a review of TTbar and JTbar - deformed CFTs and their holographic interpretation. I will then show that both TTbar and JTbar - deformed CFTs possess Virasoro x Virasoro symmetry. For the case of JTbar, I will discuss the classical realization of these symmetries in terms of field-dependent coordinate transformations and show how the associated generators can be used to define an analogue of "primary" operators in this non-local theory, whose correlation functions are entirely fixed in terms of those of the undeformed CFT.

ITMP seminar will be held on Wednesday, January 26 at 18:00. The seminar will be arranged via Zoom.

** **

### "Classical solutions and semiclassical expansion of non-relativistic strings in AdS5xS5"

**Dr. Andrea Fontanella, ITMP**

**December 15, 2021 (Wednesday)**

Abstract: The S-matrix of a theory is a key object to compute, since it encodes many physical properties of it. In this talk we present some recent work which aims to pave the ground towards an S-matrix computation for non-relativistic strings in AdS5xS5. After introducing some key features of the non-relativistic theory, we shall first address the question of how classical string solutions look like in this theory. We shall point out that every solution has a common feature, due to solving the equations of motion for the Lagrange multiplier fields. Some string solutions with closed and twisted boundary conditions will be presented, which represent the non-relativistic (and twisted) analogue of the BMN and GKP solutions for the relativistic theory. The second part of the talk focusses on the perturbative expansion in large string tension of the action around the twisted BMN-like solution. To perform this expansion we shall fix light-cone gauge and also additionally expand in large AdS radius.

ITMP seminar will be held on Wednesday, December 15 at 17:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "A Puncture in the Euclidean Black Hole"

**Prof. Nissan Itzhaki, Tel Aviv University**

**December 8, 2021 (Wednesday)**

Abstract: We consider the backreaction of the winding zero mode on the cigar geometry. We focus on the case of the $SL(2,R)_k/U(1)$ cigar associated with e.g. the near-horizon limit of $k$ NS5 black-branes. We solve the equations of motion numerically in the large $k$ limit as a function of the amplitude of the winding mode at infinity. We find that there is a critical amplitude $C_c=\exp(-\gamma/2)$ that admits a critical solution. The exact CFT description of the $SL(2,R)_k/U(1)$ cigar, in particular the FZZ duality, fixes completely the winding amplitude. We find that in the large $k$ limit there is an exact agreement $C_c=C_{FZZ}$. The critical solution is a cigar with a puncture at its tip; consequently, the BH entropy is carried entirely by the winding condensate. We argue that, in the Lorentzian case, the information is ejected from the black hole through this puncture.

ITMP seminar will be held on Wednesday, December 8 at 18:00. The seminar will be arranged via Zoom.

### "Disforming the Kerr metric"

**Dr. Timothy Anson, ITMP**

**December 1, 2021 (Wednesday)**

Abstract: Starting from a recently constructed stealth Kerr solution of higher order scalar tensor theory, I will present disformal versions of the Kerr spacetime with a constant disformal factor and a regular scalar field. While the disformed metric has only a ring singularity and asymptotically is quite similar to Kerr, it is neither Ricci-flat nor circular. Non-circularity has far reaching consequences on the structure of the solution. In particular, I will discuss the properties of important hypersurfaces in the disformed spacetime: ergosphere, stationary limit and event horizon, and highlight the differences with the Kerr metric. I will also mention experimental signatures of these spacetimes.

ITMP seminar will be held on Wednesday, December 1 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Infinite symmetries and Ward identities in celestial holography"

**Dr. Hongliang Jiang, Queen Mary University of London**

**November 24, 2021 (Wednesday)**

Abstract: Celestial holography reformulates the scattering amplitude holographically in terms of celestial conformal field theory living at boundary null infinity, thus opening up an interesting and promising avenue towards flat holography. In this talk, I will discuss various aspects of symmetry and their implications in celestial holography. I will first discuss how to realize the global symmetry of spacetime in celestial CFT, ranging from Poincare to conformal symmetry, and further to the superconformal symmetry of N=4 SYM. Then I will study the asymptotic symmetries from the celestial conformal field theory point of view. More specifically, by focusing on the soft sector of celestial OPEs, I will derive an infinite-dimensional symmetry algebra, dubbed holography chiral algebra, in supersymmetric Einstein-Yang-Mills theory. In the case of pure Einstein gravity, the holography chiral algebra turns out to be the w_{1+∞} algebra. These infinite symmetries give rise to infinite Ward identities in celestial CFT, which are equivalent to infinite soft theorems in scattering amplitudes. Finally, I will also derive general formulae for celestial OPEs and the corresponding Ward identities arising from arbitrary cubic interactions of three spinning massless particles.

ITMP seminar will be held on Wednesday, November 24 at 18:00. The seminar will be arranged via Zoom.

### "Colour-kinematic duality, double copy and homotopy algebras"

**Dr. Tommaso Macrelli, Surrey University**

**November 17, 2021 (Wednesday)**

Abstract: While colour-kinematic duality and double copy are a well established paradigm at tree level, their loop level generalisation remained for a long time an unsolved problem. Lifting the on-shell, scattering amplitude-based description to an action-based approach, we show that a theory that exhibits tree level colour-kinematic duality can be reformulated in a way such that its loop integrands manifest colour-kinematic duality. After a review of Batalin-Vilkovisky formalism and homotopy algebras, we discuss how these structures emerge in quantum field theory and gravity. We focus then on the application of these sophisticated mathematical tools to colour-kinematic duality and double copy, introducing an adequate notion of colour-kinematic factorisation. This talk is based on arXiv:2007.13803 [hep-th], arXiv:2102.11390 [hep-th], arXiv:2108.03030 [hep-th].

ITMP seminar will be held on Wednesday, November 17 at 18:00. The seminar will be arranged via Zoom.

### "Surface operators in the 6d N=(2,0) theories"

**Dr. Maxime Trepanier, ITMP**

**November 10, 2021 (Wednesday)**

Abstract: One of the surprising predictions of string theory is the existence of QFTs in 6d with superconformal symmetry known as the 6d N=(2,0) theories. These theories contain surface operators which are analogous in many ways to Wilson loops in gauge theories. In this talk I will discuss some of the properties of these operators that make them ideal observables to learn about the 6d N=(2,0) theories. After reviewing the simplest example (the sphere) both in field theory and in holography, I will discuss how supersymmetry helps to find the holographic description for more complicated surface operators. In particular, in my recent work we found the holographic description for a class of tori, and their expectation value captures a 6d analog of the quark-antiquark potential.

ITMP seminar will be held on Wednesday, November 10 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Love and Naturalness"

**Dr. Mikhail Ivanov, Princeton IAS & INR RAS**

**November 3, 2021 (Wednesday)**

Abstract: Tidal Love numbers of a compact body capture multipole moments induced by external gravitational fields. Also they appear as Wilson coefficients in the post-Newtonian effective field theory of extended objects. It has been known for a decade that Love numbers vanish identically for black holes in four dimensions, which posed a major naturalness problem in the EFT context. In my talk, I will present a new hidden (“Love”) symmetry of black holes, which elegantly resolves this naturalness paradox.

ITMP seminar will be held on Wednesday, November 3 at 18:00. The seminar will be arranged via Zoom.

### "Stress tensor and conformal correlators"

**Prof. Andrei Parnachev, Trinity College Dublin**

**October 27, 2021 (Wednesday)**

Abstract: I will describe a calculation of the contributions of stress tensor composites to correlators in CFTs (in d>2) with a large number of degrees of freedom, including holographic CFTs. Implications for holography, thermalization and possible higher spin symmetries relevant for near lightcone correlators will be discussed.

ITMP seminar will be held on Wednesday, October 27 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Sigma models as Gross-Neveu models"

**Dr. Dmitry Bykov, Steklov Mathematical Institute, ITMP MSU**

**October 20, 2021 (Wednesday)**

Abstract: I will show that there is a wide class of integrable sigma models that are exactly and explicitly equivalent to bosonic Gross-Neveu models. In full generality these are models with quiver variety phase spaces, but the familiar CP^n, Grassmannian or flag manifold sigma models belong to this class as well. This approach leads to a new take on topics such as RG (Ricci) flow, construction of integrable deformations and the inclusion of fermions. In particular, it provides a way of obtaining worldsheet SUSY theories from target space SUSY theories by means of a supersymplectic quotient.

ITMP seminar will be held on Wednesday, October 20 at 18:00. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Unitarization in Kaluza Klein theory and the Geometric Bootstrap"

**Dr. Kurt Hinterbichler, Case Western Reserve University**

**October 13, 2021 (Wednesday)**

Abstract: The infinite towers of massive particles present in Kaluza Klein reductions of Einstein gravity conspire to soften the high-energy behavior of the scattering of massive spin-2 states. The mechanism by which this occurs leads to a bootstrap procedure, analogous to the conformal bootstrap, that yields new non-trivial constraints on the eigenvalue spectra of closed Einstein manifolds.

ITMP seminar will be held on Wednesday, October 13 at 18:00. The seminar will be arranged via Zoom.

### "Non-perturbative gravitational effects in cosmology"

**Dr. Victor Gorbenko, Stanford University**

**October 6, 2021 (Wednesday)**

Abstract: I will start with reviewing some recent progress in understanding the black hole evaporation with the help of gravitational path integral methods. It turns out that for certain observables, for example the so-called Page curve for the BH entropy, higher-topology saddle points of the gravitational path integral produce important and calculable contributions. I will then discuss potential applications of similar ideas in cosmology and when such non-perturbative effects may be relevant. Then, I will demonstrate a concrete calculation in a simple toy-model, where a bra-ket wormhole, that is a connection between the bra and the ket of the wave function of the universe arises.

ITMP seminar will be held on Wednesday, October 6 at 18:00. The seminar will be arranged in the hybrid format. The talk will take place in ITMP, room G-725 while it will also be possible to participate online via Zoom.

### "Black holes in scalar-tensor theories"

**Dr. Eugeny Babichev, The University Paris-Saclay**

**September 29, 2021 (Wednesday)**

Abstract: I will review black hole solutions in Horndeski theory and its extensions. For shift symmetric theories of Horndeski and beyond Horndeski theory, black holes involve several classes of nontrivial solutions: those that include, at the level of the action, a linear coupling to the Gauss-Bonnet term and those that involve time dependence in the scalar field. I will describe black hole solutions of both classes in some detail. I will also review and discuss recent results on hairy black holes in particular subclasses of the theory.

ITMP seminar will be held on Wednesday, September 29 at 18:00. The seminar will be arranged via Zoom.

### "Black holes on a conifold with fluxes"

**Prof. Alex Buchel, Perimeter Institute**

**September 22, 2021 (Wednesday)**

Abstract: We present a comprehensive analysis of the black holes on warped deformed conifold with fluxes in Type IIB supergravity. These black holes realize the holographic dual to thermal states of the N = 1 supersymmetric SU(N) × SU(N + M) cascading gauge theory of Klebanov et al on round S^3 . There are three distinct mass scales in the theory: the strong coupling scale Λ of the cascading gauge theory, the compactification scale µ = 1/L_3 (related to the S^3 radius L_3 ) and the temperature T of a thermal state. Depending on Λ , µ and T , there is an intricate pattern of confinement/deconfinement (Hawking-Page) and the chiral symmetry breaking phase transitions.

ITMP seminar will be held on Wednesday, September 22 at 18:00. The seminar will be arranged via Zoom.

** **

### "Comments on Large Charge and N=4 SYM"

**Dr. Shota Komatsu, CERN and Princeton IAS**

**June 16, 2021 (Wednesday)**

Abstract: I will discuss three topics on the large charge limit of N=4 super Yang-Mills and its holographic dual. First, I will discuss what we can learn from holography about general structures of the large-charge expansion of SCFT with higher-rank gauge groups. Second, I will briefly discuss the double-scaling limit and their relation to the central extension of the symmetry. Third I will explain how the ideas from the large-charge expansion help to resolve confusions in the literature on the holographic computation of correlation functions of heavy operators dual to D-branes in AdS.

ITMP seminar will be held on Wednesday, June 16 at 18:00. The seminar will be arranged via Zoom.

### "Integrable Systems and Spacetime Dynamics"

**Kristiansen Lara, University of Santiago, Chile**

**June 9, 2021 (Wednesday)**

Abstract: It is shown that the Ablowitz-Kaup-Newell-Segur (AKNS) integrable hierarchy can be obtained as the dynamical equations of three-dimensional General Relativity with a negative cosmological constant. This geometrization of AKNS system is possible through the construction of novel boundary conditions for the gravitational field. These are invariant under an asymptotic symmetry group characterized by an infinite set of AKNS commuting conserved charges. Gravitational configurations are studied by means of $SL(2,\mathbb{R})$ conjugacy classes. Conical singularities and black hole solutions are included in the boundary conditions. Based on https://arxiv.org/abs/2104.09676.

ITMP seminar will be held on Wednesday, June 9 at 18:00. The seminar will be arranged via Zoom.

### "Celestial CFT Correlators and Conformal Block Decomposition"

**Dr. Angelos Fotopoulos, Northeastern University, Boston**

**June 2, 2021 (Wednesday)**

Abstract: I will shortly review the connection of the Bondi-van der Burg-Metzner-Sachs (BMS) symmetry group of asymptotically flat four-dimensional spacetimes at null infinity to the S-matrix of elementary particles and gravitons.

Applying Mellin transformations to traditional, momentum space amplitudes we can compute celestial amplitudes. These are conjectured to correspond to correlators of conformal primary fields on a putative two-dimensional celestial sphere. I will elaborate on the proposal of flat holography in which four-dimensional physics is encoded in two-dimensional celestial conformal field theory (CCFT). The symmetry underlying CCFT is the extended BMS symmetry of (asymptotically) flat spacetime. I will show how to use soft and collinear theorems of Einstein-Yang-Mills theory to derive the OPEs of BMS field operators generating the symmetries of the BMS group, superrotations and supertranslations.

In the second part of my talk, time permitted, I will discuss a proposal for radial quantization of the CCFT and I will present an attempt to decompose gluon celestial amplitudes in conformal blocks. This will reveal some very interesting aspects of the Celestial CFT: the emergence of new operators in the theory and space-time scattering channels which lead to continuous complex spin primary fields. The space-time interpretation of these operators is still unclear. Moreover, CFT crossing symmetry and its relation to four-dimensional spacetime crossing symmetry of the S-matrix are some interesting open problems.

ITMP seminar will be held on Wednesday, June 2 at 19:30. The seminar will be arranged via Zoom.

### "Inflation and reheating with Higgs inflation and related models"

**Dr. Fedor Bezrukov, University of Manchester**

**May 26, 2021 (Wednesday)**

Abstract: Using the Higgs field for inflation is an economic way to solve two problems with one scalar field -- Higgs field is require in the Standard Model, and a scalar field is the simplest method to drive inflation of the early Universe. However, consistent attempt to do this takes us to the limits of validity of the quantum field theory, and significant problems with the reheating after inflation. I’ll discuss the ways to deal with this by combining the theory with R^2 gravitational terms, and describe the highly nontrivial dynamics of the system after inflation.

ITMP seminar will be held on Wednesday, May 26 at 18:00. The seminar will be arranged via Zoom.

### "Probing boundary states at finite coupling"

**Dr. Edoardo Vescovi, KTH Royal Institute of Technology, Stockholm University**

**May 19, 2021 (Wednesday)**

Abstract: In this talk, we calculate exactly the correlation function of a Wilson loop operator and a local non-BPS operator in planar N=4 SYM. First, we introduce an effective theory for such observable in free theory and we reformulate the gauge-theory computation as an overlap between an energy eigenstate of a spin-chain and a matrix product state. The form of the result supports the interpretation of the correlator as an overlap between an integrable boundary state, which we determine using symmetry and integrability, and the state corresponding to the single-trace operator. Second, we explain how to formulate a non-perturbative bootstrap program based on the results obtained in this framework.

We also discuss two applications of the effective theory to the four-point function of determinant operators in N=4 SYM, as well as to all-loop determinant correlators in the fishnet theory.

ITMP seminar will be held on Wednesday, May 12 at 18:00. The seminar will be arranged via Zoom.

### "Thermal correlators in CFT and black holes"

**Prof. Jorge Guillermo Russo, Catalan Institution for Research and Advanced Studies and University of Barcelona, Barcelona**

**May 12, 2021 (Wednesday)**

Abstract: We describe the computation of thermal 2-point correlation functions in the black brane AdS5 background dual to 4d CFT's at finite temperature for operators of large scaling dimension. This gives rise to a formula that matches the expected structure from the OPE. The thermal 2-point function has an exponentiation property, whose origin we explain. We also compute the first correction to the two-point function due to graviton emission, which encodes the time travel to the black hole singularity.

We will also discuss some interesting features of higher-point functions.

ITMP seminar will be held on Wednesday, May 12 at 18:00. The seminar will be arranged via Zoom.

### "Exceptional world-volume currents and their algebras"

**Dr. David Osten, ITMP**

**May 5, 2021 (Wednesday)**

Abstract: After a short review of exceptional generalised geometry I will introduce a unified setup for a duality-covariant Hamiltonian formulation of world-volume theories of objects in string and M-theory. Based on https://arxiv.org/abs/2103.03267

ITMP seminar will be held on Wednesday, May 5 at 18:00. The seminar will be arranged via Zoom.

### "Models for a vast energy range: particles meet gravity and cosmology"

**Dr. Alberto Salvio, University of Rome Tor Vergata**

**April 21, 2021 (Wednesday)**

Abstract: I will discuss models valid over a vast energy range by following 2 strategies. In one approach (bottom-up) I will illustrate the main phenomenological aspects of a scenario where one adds to the Standard Model 3 right-handed neutrinos and an axion sector. This can account for neutrino oscillations, dark matter, baryogengesis, inflation and can also stabilize the electroweak vacuum. In another, more ambitious approach, I will talk about a scenario where all couplings flow to zero at infinite energy (total asymptotic freedom). The corresponding phenomenology of this top-down approach will also be treated.

ITMP seminar will be held on Wednesday, April 21 at 18:00. The seminar will be arranged via Zoom.

### "Losing the trace to discover dynamical Newton or Planck constants"

**Dr. Alexander Vikman, Institute of Physics of the Czech Academy of Sciences, Prague **

**April 14, 2021 (Wednesday)**

Abstract: I will discuss our recent work e-Print: 2011.07055. There we showed that promoting the trace part of the Einstein equations to a trivial identity results in the Newton constant being an integration constant. Thus, in this formulation the Newton constant is a global dynamical degree of freedom which is also a subject to quantization, quantum fluctuations and the Heisenberg uncertainty relations. This is similar to what happens to the cosmological constant in the unimodular gravity where the trace part of the Einstein equations is lost in a different way. I will consider a constrained variational formulation of these modified Einstein equations. Then, drawing on analogies with the Henneaux-Teitelboim action for unimodular gravity, I will discuss different general-covariant actions resulting in these dynamics. In this approach, it turned out that the inverse of the dynamical Newton constant is canonically conjugated to the Ricci scalar integrated over spacetime. Surprisingly, instead of the dynamical Newton constant one can formulate an equivalent theory with a dynamical Planck constant. Finally, I will show that an axion-like field can play a role not only of the cosmological constant, as in e-Print: 2001.03169, but also of the Newton constant or even of the Planck constant.

ITMP seminar will be held on Wednesday, April 14 at 18:00. The seminar will be arranged via Zoom.

** **

### "Supergravity excitations of stringy geometries"

**Associate Prof. Oleg Lunin, SUNY-Albany**

**April 7, 2021 (Wednesday)**

Abstract: Motivated by the desire to understand the dynamics of light modes on various gravitational backgrounds, this talk summarizes recent results concerning properties of scalar, vector, and tensor excitations of black holes and integrable stringy geometries. For rotating black holes and for certain Wess-Zumino-Witten models, full separability of all dynamical equations is demonstrated, and symmetries underlying this property are uncovered. For other classes of integrable backgrounds, the energy spectra of various fields are evaluated, and the algebraic constructions of the corresponding eigenfunctions are presented.

ITMP seminar will be held on Wednesday, April 7at 18:00. The seminar will be arranged via Zoom.

### "Integrated four-point correlators in N=4 SYM"

**Dr. Congkao Wen, Queen Mary University of London**

**March 31, 2021 (Wednesday)**

Abstract: In this talk, we will discuss integrated correlators of four superconformal primaries in N=4 super Yang-Mills, that are defined by integrating over spacetime coordinates of the four-point correlator with certain integration measures. The integrated correlators can be computed using supersymmetric localisation, which are expressed as N-dimensional matrix-model integrals. We will mostly focus on one of the integrated correlators. We find that this integrated correlator can be presented as a lattice sum, which makes manifest the SL(2, Z) modular invariance of N=4 SYM. Furthermore, the integrated correlator obeys a remarkable Laplace-difference equation, which relates the correlator of SU(N) theory with those of SU(N-1) and SU(N+1) theories. The expression allows us to obtain exact results of the integrated correlator in various limits. For instance, in perturbation, the expression is checked to be consistent with known results in the literature; in the large-N limit, it is shown to match with the expected results from string theory due to AdS/CFT duality.

ITMP seminar will be held on Wednesday, March 31 at 18:00. The seminar will be arranged via Zoom.

### "Towards the Virasoro-Shapiro Amplitude in AdS5xS5"

**Prof. Paul Heslop, Durham University**

**March 24, 2021 (Wednesday)**

Abstract: We propose a systematic procedure for obtaining all single trace 1/2-BPS correlators in N=4 super Yang-Mills corresponding to the four-point tree-level amplitude for type IIB string theory in AdS5xS5. The underlying idea is to compute generalised contact Witten diagrams coming from a 10d effective field theory on AdS5xS5 whose coefficients are fixed by the flat space Virasoro-Shapiro amplitude up to ambiguities related to commutators of the 10d covariant derivatives which require additional information such as localisation. We illustrate this procedure by computing stringy corrections to the supergravity prediction for all single trace 1/2-BPS correlators up to O(α′7), and spell out a general algorithm for extending this to any order in α′.

ITMP seminar will be held on Wednesday, March 24 at 18:00. The seminar will be arranged via Zoom.

### "Chaotic scattering with a highly excited string"

**Dr. Vladimir Rosenhaus, Institute for Advanced Study, Princeton**

**March 17, 2021 (Wednesday)**

Abstract: Motivated by the desire to understand chaos in the S-matrix of string theory, we study tree level scattering amplitudes involving highly excited strings. While the amplitudes for scattering of light strings have been a hallmark of string theory since its early days, scattering of excited strings has been far less studied. Recent results on black hole chaos, combined with the correspondence principle between black holes and strings, suggest that the amplitudes have a rich structure. We review the procedure by which an excited string is formed by repeatedly scattering photons off of an initial tachyon. We compute the scattering amplitude of one arbitrary excited string decaying into two tachyons, and study its properties for a generic excited string. We find the amplitude is highly erratic as a function of both the precise excited string state and of the tachyon scattering angle.

ITMP seminar will be held on Wednesday, March 17 at 18:00. The seminar will be arranged via Zoom.

Presentation

### "Spinning and spinless two-particle dynamics from gravitational scattering amplitudes"

**Prof. Radu Roiban, Penn State University**

**March 10, 2021 (Wednesday)**

Abstract: In the appropriate classical limit, scattering amplitude-based techniques can yield the classical interaction of massive bodies at fixed order in the post-Minkowskian expansion.

In this talk we review a framework for the construction of the two-body Hamiltonian for compact binary systems and illustrate it with state of the art results for both spinning and spinless systems. Throughout we emphasize structure of gravitational interactions and direct relations between scattering amplitudes and observables of two-particle dynamics.

ITMP seminar will be held on Wednesday, March 10 at 18:00. The seminar will be arranged via Zoom.

### "O(D,D) and string alpha'-corrections"

**Linus Wulff, Masaryk University**

**March 3, 2021 (Wednesday)**

Abstract: String theory on a d-dimensional torus features an O(d,d) symmetry. It has been suggested that the low-energy effective action can be formulated with a larger O(D,D) symmetry, even before putting the theory on a torus. This approach, which goes by the name of Double Field Theory (DFT), has proven very useful. I will address the problem of constructing higher derivative invariants in this formalism. In agreement with the literature we find that a quadratic Riemann invariant can be constructed, which can account for the first alpha'-correction to the bosonic and heterotic string. However, we find that no cubic or quartic Riemann invariants can be constructed. This suggests that the quartic Riemann terms arising at order alpha'^3 in string theory do not have a DFT embedding.

ITMP seminar will be held on Wednesday, March 3 at 18:00. The seminar will be arranged via Zoom.

### "Gravity as a double copy of gauge theory"

**Ricardo Monteiro, Queen Mary University of London**

**February 24, 2021 (Wednesday)**

Abstract: Relations expressing gravity as a "double copy" of gauge theory appeared first in string theory, and have been used to compute scattering amplitudes in theories of gravity, with applications to both theory and phenomenology. I will discuss how the double copy extends to solutions to the equations of motion, including our best known black hole spacetimes, and how this story connects to the original story for scattering amplitudes.

ITMP seminar will be held on Wednesday, February 24 at 18:00. The seminar will be arranged via Zoom.

### "Holographic correlators and emergent Parisi-Sourlas supersymmetry"

**Xinan Zhou, Princeton University**

**February 17, 2021 (Wednesday)**

Abstract: In this talk, I will first review the recent progress in computing holographic four-point correlators in maximally supersymmetric CFTs. I will introduce the so-called Maximally R-symmetry Violating (MRV) limit, in which the Mellin amplitudes drastically simplify and become easy to compute. From the MRV limit, I will show that the full amplitudes can be reconstructed by using symmetries. This gives a complete answer to all tree-level four-point functions in all three maximally supersymmetric backgrounds AdS4xS7, AdS5xS5, and AdS7xS4. In the second part of my talk, I will point out that these results have surprising properties. The Mellin amplitudes exhibit an emergent dimensional reduction structure, which allows them to be expressed in terms of only scalar exchange amplitudes from lower dimensional spacetimes. I will explain that this dimensional reduction structure is closely related to a holographic realization of the Parisi-Sourlas supersymmetry.

ITMP seminar will be held on Wednesday, February 17 at 18:00. The seminar will be arranged via Zoom.

### "Scattering from production in 2d"

**Piotr Tourkine, Paris LPTHE, CERN**

**February 3, 2021 (Wednesday)**

Abstract: In this seminar, I will talk about recent results about a numerical method to find unitary S-matrices. The method, based on works of Atkinson, was invented in the late 60s and was used as a proof of existence of functions that satisfy all of the S-matrix axioms in 4d. However, it was not put in practical use. Our recent results concern the implementation of those methods for S-matrices in two dimensions, using two different iterative schemes: a fixed-point iteration and Newton's method. Those schemes iterate the unitarity and dispersion relations, and converge to solutions to the S-matrix axioms. This numerical strategy provides a solution to the problem of reconstructing the scattering amplitude starting from a given particle production probability. After a general introduction, the talk will be focused on how we implemented the algorithms, what they converge to, and the conditions under which they converge. We will see that the question of convergence naturally connects to the recent study of the coupling maximization in the two-dimensional S-matrix bootstrap. If time allows, I'll also comment on a fractal structure which we observed to be related to the so-called CDD-ambiguities. I'll conclude with possible future directions.

ITMP seminar will be held on Wednesday, February 3 at 18:00. The seminar will be arranged via Zoom.

### "The O(N) vector model at large charge: EFT, large N and resurgence"

**Dr. Domenico Orlando, INFN Turin, University of Bern**

**January 27, 2021 (Wednesday)**

Abstract: I will discuss the IR fixed point of the O(N) vector model in 3 dimensions (Wilson-Fisher point) in the framework of the large charge expansion. First I will construct an EFT valid for any N, then verify the prediction of the model in the double scaling limit of large N, large charge and finally discuss the use of resurgence to extend the validity of the EFT to sectors of small charge.

ITMP seminar will be held on Wednesday, January 27 at 18:00. The seminar will be arranged via Zoom.

### "Loops in Holography"

**Prof. Ivo Sachs, Ludwig Maximilian University of Munich**

**December 16, 2020 (Wednesday)**

Abstract: A quantum field theory (QFT) in an (Anti-)de Sitter, (A-)dS space-time can be characterised by a conformal field theory (CFT) much like the S-matrix for Minkowski QFT’s. I will review how quantum loops are reflected in CFT, both in AdS and dS. The latter has a remote connection to density perturbations in the Universe.

ITMP seminar will be held on Wednesday, December 16 at 18:00. The seminar will be arranged via Zoom.

### "RG Limit Cycles and "Spooky" Fixed Points in Perturbative QFT"

**Fedor Popov, Princeton University**

**December 9, 2020 (Wednesday)**

Abstract: We study quantum field theories with sextic interactions in 3−ϵ dimensions, where the scalar fields ϕab form irreducible representations under the O(N)2 or O(N) global symmetry group. We calculate the beta functions up to four-loop order and find the Renormalization Group fixed points. In an example of large N equivalence, the parent O(N)2 theory and its anti-symmetric projection exhibit identical large N beta functions which possess real fixed points. However, for projection to the symmetric traceless representation of O(N), the large N equivalence is violated by the appearance of an additional double-trace operator not inherited from the parent theory. Among the large N fixed points of this daughter theory we find complex CFTs. The symmetric traceless O(N) model also exhibits very interesting phenomena when it is analytically continued to small non-integer values of N. Here we find unconventional fixed points, which we call "spooky." They are located at real values of the coupling constants gi, but two eigenvalues of the Jacobian matrix ∂βi/∂gj are complex. When these complex conjugate eigenvalues cross the imaginary axis, a Hopf bifurcation occurs, giving rise to RG limit cycles. This crossing occurs for Ncrit≈4.475, and for a small range of N above this value we find RG flows which lead to limit cycles.

ITMP seminar will be held on Wednesday, December 9 at 18:00. The seminar will be arranged via Zoom.

### "Large-N localization and quiver CFT"

**Prof. Konstantin Zarembo, Niels Bohr Institute, Nordita**

**December 2, 2020 (Wednesday)**

Abstract: The quiver CFT interpolates between N=4 SYM and N=2 super-QCD, and is dual to strings on the AdS5 x S5/Z2 orbifold. Localization of the path integral in the quiver CFT potentially gives means to test this duality rigorously. The strong-coupling solution of the localization matrix model, which I will describe, is in the remarkable qualitative agreement with the holographic dual, but is not devoid of puzzling features.

ITMP seminar will be held on Wednesday, December 2 at 18:00. The seminar will be arranged via Zoom.

### "Scattering in chiral strong backgrounds"

** Dr. Tim Adamo, University of Edinburgh**

**November 25, 2020 (Wednesday)**

Abstract: There are many reasons to be interested in quantum field theory in the presence of strong, non-perturbative background fields, but surprisingly little is known in these scenarios, especially when compared to trivial backgrounds. For instance, the full semi-classical S-matrices of gauge theory and gravity are known in a trivial background, but even for simple strong backgrounds the tree-level amplitudes of these theories have not been computed beyond four-external particles. This raises the question: are all-multiplicity formulae (and other hallmarks of the study of scattering amplitudes in recent years) inextricably tied to trivial backgrounds? In this talk, I will demonstrate that for a broad class of chiral backgrounds in four-dimensions, we can find all-multiplicity expressions for tree-level scattering amplitudes of gauge theory and gravity which are remarkably simple and clearly un-related to standard background-coupled field theory on space-time.

ITMP seminar will be held on Wednesday, November 25 at 18:00. The seminar will be arranged via Zoom.

### "Closed strings and weak gravity condition from higher-spin causality"

**Dr. Sandipan Kundu, Johns Hopkins University**

**November 18, 2020 (Wednesday)**

Abstract: I will show that metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. Another consequence of this bound is that all metastable higher spin particles in 4d with masses below the string scale must satisfy a weak gravity condition. Moreover, these bounds also have surprising implications for large N QCD coupled to gravity.

ITMP seminar will be held on Wednesday, November 18 at 18:00. The seminar will be arranged via Zoom.

### "Event shapes, the light-ray OPE and superconvergence"

**Dr. Alexander Zhiboedov, CERN**

**November 11, 2020 (Wednesday)**

Abstract: I will describe recent progress in understanding event shapes in conformal field theories. Familiar from the description of hadronic events at colliders, these observables are computed by matrix elements of the so-called light-ray operators. Characterizing the light-ray operators in a nonperturbative setting poses many theoretical challenges. I will describe some of the recently developed tools to perform computations of conformal event shapes and illustrate them using N=4 SYM. Finally, I will explain how via holography some of the basic properties of conformal event shapes lead to nontrivial sum rules obeyed by possible UV completions of general relativity.

ITMP seminar will be held on Wednesday, November 11 at 18:00. The seminar will be arranged via Zoom.

### "Modification of the radiation definition in odd dimensions"

**Mikhail Khlopunov, ITMP**

**October 28, 2020 (Wednesday)**

Abstract: In this seminar, I will discuss modification of the radiation definition for the case of odd-dimensional space-time. The standard definition of the wave zone fails in odd dimensions, due to the violation of the Huygens principle: the signal from an instantaneous flash of current reaches an observer after an interval of time required for propagation of the signal at the speed of light, but then the tail is observed endlessly; while in even-dimensional spaces an instant signal ends instantly at the observation point. The reason is that the retarded Green’s functions of the wave equation in odd dimensions has support localised not only on the light cone, but also inside it. I will discuss the covariant retarded quantities technique and Rohrlich-Teitelboim definition of the wave zone. Using this definition, the scalar radiation from a point-like charge, moving along the circular trajectory in three and five-dimensional space-times, will be computed. The obtained results will be verified by the calculations of the spectral distributions of the radiated energy, which are indifferent to the dimensionality of the space-time. Also, the contributions of the tails to the radiation will be discussed.

ITMP seminar will be held on Wednesday, October 28 at 18:00. The seminar will be arranged via Zoom.

### "On double elliptic integrable system: characteristic determinant and Manakov triple"

**Dr. Andrei Zotov, Steklov Mathematical Institute RAS**

**October 21, 2020 (Wednesday)**

Abstract: We discuss double elliptic integrable systems, where the dependence on the momenta of particles is elliptic. These models generalize the relativistic Ruijsenaars integrable systems, which contain trigonometric (exponential) dependence on momenta. A brief review on underlying dualities and interrelations between integrable systems will be given. We explain how to construct a kind of determinant representation for the known conservation laws. Finally, we will see that in the classical case the double elliptic models are naturally described by the Manakov L-A-B triple instead of the Lax pair.

ITMP seminar will be held on Wednesday, October 21 at 18:00. The seminar will be arranged via Zoom.

### "Production of massive particles from the decay of a free massless field"

**Dr. Ariel Arza, ITMP**

**October 07, 2020 (Wednesday)**

Abstract: In this talk we will show, in a simple toy model (H=g\phi\chi^2), how Bose enhancement allows the decay of a massless field into massive particles. It happens due to a parametric resonance caused by a big energy density of the decaying field. I will show the instability conditions as well as the energy density threshold for the decay to occur. I will also compute the equivalent of the spontaneous decay rate.

ITMP seminar will be held on Wednesday, October 07 at 18:00. The seminar will be arranged via Zoom.

### "Hamiltonian structures of the spin Ruijsenaars-Schneider models"

**Prof. Gleb Arutyunov, University of Hamburg**

**September 30, 2020 (Wednesday)**

Abstract: TBA

ITMP seminar will be held on Wednesday, September 30 at 18:00. The seminar will be arranged via Zoom.

### "Constrained modified gravities: generalized unimodular gravity and beyond"

**Nikita Kolganov, ITMP**

**September 23, 2020 (Wednesday)**

Abstract: In my talk, I will give you a brief introduction into modified gravity theories, and then I will proceed to particular modified gravity models, which I'm interested in. Most of the modified gravities are equivalent to the General Relativity, equipped with some additional degrees of freedom. In our case these d.o.f. are obtained by the explicit breaking of general covariance by an algebraic constraint on metric coefficients. I'm going to discuss the covariantization issue of such theories, its duality to well-known k-essence and self-gravitating media models, and applications to inflationary cosmology.

ITMP seminar will be held on Wednesday, September 23 at 18:00. The seminar will be arranged via Zoom.

### "Schwarzschild black hole thermodynamic entropy on a nice slice"

**Dr. Jose Alejandro Rosabal, Asia Pacific Center for Theoretical Physics, Pohang**

**July 22, 2020 (Wednesday)**

Abstract: In this seminar I will present the calculation of the thermodynamic entropy of a Schwarzschild black hole on a nice slice. This can be seen as a warm up to address the calculation of the Von Neumann entropy for two intervals, that includes a portion of the interior of the black hole, and the Page curve. In the end I will comment on the relation between this work and some recent proposal.

ITMP seminar will be held on Wednesday, July 22 at 14:00. Given the situation the seminar will be arranged via Zoom.

### "Gauge/gravity duality and the phenomenology of hadrons"

**Dr. Frederic Brunner, Vienna University of Technology (TU Wien)**

**July 8, 2020 (Wednesday)**

Abstract: I will give a pedagogical introduction to aspects of hadronic physics at low energy, and show how the methodology of gauge/gravity duality may be applied to certain problems arising in this context. As a concrete example, I will talk about the search for glueballs, bound states of gluons predicted by lattice gauge theory. These states have not been identified unambiguously among the hadrons we observe in collider experiments, in part due to the lack of theoretical predictions of their decay rates. I will show how gauge/gravity duality can be used to calculate glueball decay rates, and discuss potential implications.

ITMP seminar will be held on Wednesday, July 8 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "Current Algebra and Generalised Geometry"

**Dr. David Osten, Ludwig Maximilian University/Max-Planck-Institute for Physics, Munich**

**June 24, 2020 (Wednesday)**

Abstract: The first part of the talk will be a review of T-duality and generalised geometry in string theory. Generalised geometry is a generalisation of Riemannian geometry that captures certain 'non-geometric' backgrounds which are nevertheless well-defined in string theory. A convenient characterisation of such backgrounds is given in terms of the so-called generalised fluxes. In the second part of the talk I want to discuss the meaning of these generalised fluxes in the worldsheet theory. There, they describe a deformation of the canonical Poisson structure -- namely the current algebra. Besides applications to magnetic backgrounds and integrable sigma models which motivated this work, the virtue of the deformed current algebra lies in the fact that it gives clear-cut routes to non-commutative and non-associative interpretations of the generalised flux backgrounds, to generalisations of T-duality and to generalisations to M-theory.

ITMP seminar will be held on Wednesday, June 24 at 18:00. Given the situation the seminar will be arranged via Zoom.

### “Introduction to the TT̄ deformation”

**Dr. Riccardo Conti, Turin University**

**June 10, 2020 (Wednesday)**

Abstract: In this talk I will give a pedagogical introduction to a special irrelevant deformation of 2-dimensional Quantum Field Theories, the so-called TT̄ deformation, which has recently attracted the attention of the theoretical physics community due to the interesting links with string theory and the AdS/CFT correspondence. I will review some basic aspects of this deformation and describe the principal features of the deformed models both at classical and quantum level. Finally, I will briefly comment on other similar irrelevant deformations and present a series of interesting open questions that still wait for answers.

ITMP seminar will be held on Wednesday, June 10 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "Efficient Rules for All Conformal Blocks: A Dream Come True"

**Dr. Valentina Prilepina, Laval University**

**May 27, 2020 (Wednesday)**

Abstract: In this talk, I will lay out a set of efficient rules for computing d-dimensional global conformal blocks in arbitrary Lorentz representations in the context of the embedding space operator product expansion (OPE) formalism. With these rules in place, the general procedure for determining all possible conformal blocks is reduced to (1) identifying the relevant group theoretic quantities and (2) applying the conformal rules to obtain the blocks. The rules represent a systematic prescription for computing the blocks in a convenient mixed OPE-three-point- function basis as well as a set of rotation matrices, which are necessary to translate these blocks to the pure three-point function basis relevant for the conformal bootstrap. I will start by tracing their origin by describing some of the essential ingredients present in the formalism that naturally give rise to these rules. I will then map out the derivation of the rules, first outlining the general algorithm for the rotation matrices and then proceeding to the conformal blocks. Along the way, l will introduce a convenient diagrammatic notation (somewhat reminiscent of Feynman diagrams), which serves to encode parts of the computation in a compact form. Finally, I will treat several interesting examples to demonstrate the application of these rules in practice.

ITMP seminar will be held on Wednesday, May 27 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "The echo method for axion dark matter detection"

**Dr. Ariel Arza, ITMP**

**May 13, 2020 (Wednesday)**

Abstract: The echo method is a new idea for axion dark matter search. It relies on the stimulated decay of cold axions into two photons when a powerful beam of microwave radiation is shot to the space. From the axion decay, a feeble but detectable amount of electromagnetic radiation is received nearby the location where the outgoing beam was released. In this talk I will describe the essentials of this idea as well as the challenges for the future.

ITMP seminar will be held on Wednesday, May 13 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "Polyvector deformations in supergravity and the string/M-theory dynamics"

**Dr. Ilya Bakhmatov, ITMP**

**April 29, 2020 (Wednesday)**

Abstract: Integrability preserving Yang-Baxter deformations of the string sigma-model have a simple supergravity description. We will review how introducing an extra bi-vector field to account for the r-matrix, one recovers the YB deformations after the simple open/closed string map. Things can be made clearer by using the formalism of double field theory, a T-duality covariant description of supergravity defined on an extended spacetime. We will discuss generalisations to the tri-vector deformations of d=11 supergravity and potential consequences for the fundamental membrane dynamics.

ITMP seminar will be held on Wednesday, April 29 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "Review on higher-spin theories"

**Dr. Dmitry Ponomarev, ITMP**

**April 15, 2020 (Wednesday)**

Abstract: I will start by explaining what is meant by higher-spin theories. Then I will illustrate why making higher-spin fields interact is not easy. I will then review the standard no-go theorems for higher-spin interactions. Next, I will discuss different approaches to circumvent these no-go’s and review the most successful attempts. Finally, I will discuss some potentially promising directions for future research.

ITMP seminar will be held on Wednesday, April 15 at 18:00. Given the situation the seminar will be arranged via Zoom.

### "Some aspects of massive gravity and Horndeski theory"

**Prof. Mikhail S. Volkov (Université de Tours, France)**

**March 26, 2020 (Thursday)**

Abstract: In the first part of the talk I plan to give a very brief introduction to the ghost-free massive gravity theory and then briefly describe the recent work on the theory of massive gravitons in arbitrary spacetimes. In the second part, I would like to present some new results obtained in the context of the Horndeski theory, in particular concerning the Palatini analysis of this theory.

ITMP seminar will be held on Thursday, March 26 at 16:00. Given the situation the seminar will be arranged via Skype.

### Доклад Марка Энно (Marc Henneaux), профессора Брюссельского Свободного университета "Asymptotic symmetries of electromagnetism and gravity".

**9 октября (среда)**

Марк Энно - известный физик-теоретик, профессор Брюссельского Свободного университета, директор Международного Сольвеевского института физики и химии (Бельгия), профессор Collège de France. Лауреат ряда престижных международных премий, включая Francqui Prize, Humboldt Research Award, Премию имени Н.Н. Боголюбова (ОИЯИ).

Аннотация доклада: The asymptotic symmetries of gravity and electromagnetism are remarkably rich. The talk will explain the asymptotic structure of gravity and electromagnetism in the asymptotically flat case by making central use of the Hamiltonian formalism. In particular, how the relevant infinite-dimensional asymptotic symmetry groups emerge at spatial infinity, and the extension to higher spacetime dimensions, will be discussed.

Доклад может быть интересен научным сотрудникам, студентам старших курсов и аспирантам, специализирующимся в теоретической физике. Рабочий язык - английский.

Начало в 18:00.

Адрес: Ломоносовский корпус МГУ, ауд. Г-716.