Институт теоретической и математической физики

МГУ имени М.В. Ломоносова

# Научный семинар

Если Вы хотели бы подписаться на рассылку о семинарах ИТМФ, пожалуйста, напишите по электронному адресу: seminar@itmp.msu.ru

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

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

, 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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

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

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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### “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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### "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.

Presentation

### 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.