Research Seminar

Understanding why Witten indices reproduce the exponential of the Bekenstein--Hawking entropy of supersymmetric black holes—despite counting bosonic and fermionic states with opposite signs—has remained a long-standing puzzle in string theory and gauge/gravity duality. In this talk we will address this question in the canonical example of the duality between four-dimensional maximally supersymmetric Yang--Mills theory and ten-dimensional Type IIB supergravity/string theory. Concretely, we wil…

The talk is devoted to discussing the Euclidean wormhole solutions in holographic models and their key role in the state-counting interpretation of the black hole entropy. In the first half of the talk I will demonstrate the emergence of wormhole-type solutions on the example of replica-nondiagonal solutions in the SYK model. In the second half of the talk I will introduce the partially entangled thermal states and their gravity duals as candidates for the black hole microstates. I will expla…

Topological defects produced during cosmological phase transitions can act as nontrivial sources of cosmological perturbations due to their anisotropic stress and internal dynamics. In this work we construct a closed framework of cosmological perturbation theory applicable to defect networks, focusing on domain walls as a concrete example. Within this framework we derive the perturbation equations sourced by the effective stress-energy tensor of the domain wall network and compute the resulti…

In this talk I will discuss Euclidean wormholes with two asymptotic AdS boundaries. I will start with a review of the Factorization puzzle and its potential resolutions. Then I will present wormhole solutions in Einstein gravity plus matter and their properties by computing expectation values of local and non-local observables, based on which I will propose possible holographic duals. I will end with a top-down bubbling wormhole construction in IIB string theory that is ½ BPS and I will propo…

I will discuss the calculations of holographic one-point functions in the presence of probe branes, paying close attention to the case of extremal correlators. These are dual to correlation functions of operators whose dimension scale with N_c and single trace operators. I will review previous approaches in the literature, emphasizing the mismatch between the holographic computation of extremal correlators and the results obtained from N=4 SYM. We will see that the tension between string theo…

I will discuss the construction of a map between weak (gauge) and strong (string) coupling degrees of freedom for the supersymmetric Wilson line-defect in the planar N=4 Super-Yang-Mills theory. By analysing the Partition Functions at zero and infinite coupling, I will propose a map from degrees of freedom capturing single- and singlet two-particle states at zero coupling to infinite coupling. This map predicts that the dimension of states in these particular sectors doubles as it goes from z…

The long-range nature of interactions in four-dimensional quantum gravity renders the standard formulation of scattering theory inapplicable and leads to infrared divergences in perturbative amplitudes. To construct a simple class of infrared-finite observables, we focus on inclusive quantities and investigate energy correlators. These observables characterize the asymptotic energy flux in scattering processes and have a long history in collider physics, particularly in the study of QCD dynam…

We investigate a range of non-singular cosmological scenarios within the framework of Horndeski gravity. In particular, we construct a bouncing Universe model and propose a minimal setup that realizes a non-pathological Genesis scenario. Both constructions allow for a fully stable transition to the kination epoch, during which General Relativity (GR) is restored. These scenarios successfully evade the no-go theorem, almost at the expense of potential strong-coupling issues in the early phase.…

In this talk we review a non-standard approach to renormalization, which is based on the Callan-Symanzik system of differential equations. It turns out that in this approach, no divergences arise during the calculations (for example, correlation functions or corrections to the effective potential). It will be shown in detail how this formulation can be applied to the renormalizable phi^4 theory. Within this approach, the effective potential, as well as two- and four-point correlation function…