### Degeneration, Geometry and Duality

**19 December 2023, 14:00**

**19 December 2023, 14:00**

Black holes have been celebrated as "the Hydrogen Atom of the 21st century". From the perspective of classical gravity, a black hole is the simplest object we know of. At the same time, it possesses huge entropy, hinting at an incredibly complex microstructure: understanding this complexity falls in the realm of quantum gravity. In this talk I will review recent results concerning the microscopics and the thermodynamics of black holes, especially in the context of holography. I will focus in particular on the thermodynamics of the fast spinning black holes, and I will describe how recently developed techniques (in collaboration with D. Kapec, A. Sheta and A. Strominger) allowed to compute the quantum corrections to the entropy of near-extremal Kerr black holes, resolving some of the long-standing puzzles concerning the low temperature limit of black hole thermodynamics.

**12 December 2023, 14:00**

I introduce a new class of defects in conformal field theory (CFT), termed orientifold defects. These defects arise from quotienting the spacetime by a Z_2 automorphism, and provide higher-codimension generalizations of CFT on a real projective space (RP_d). The orientifold defects of codimension-p preserve the SO(d-p-1)xSO(p) subgroup of the conformal group, and the two-point functions of local operators in their presence satisfy the orientifold crossing equation, which we present. In contrast to standard conformal defects, both channels of the crossing equation involve bulk operators only, and operators localized on the defect are absent. I will then present a classification of half-BPS orientifold defects in N=4 SYM and provide evidence that they preserve integrability of planar N=4 SYM and are holographic dual to orientifolds in type IIB string theory on AdS_5 times S^5.

**5 December 2023, 14:00**

Recent years have seen a surge of interest in computing classical gravitational observables via scattering-amplitude methods, in the context of binary black-hole systems. Remarkably, Kerr black holes and their gauge-theory counterpart, the root-Kerr solution, were shown to be connected to a special class of amplitudes for massive higher-spin particles. Elegant three-point amplitudes are known for any spin, however constructing the corresponding four-point Compton amplitudes is an open problem. In this talk, I will discuss the origin of the Kerr three-point amplitudes from a higher-spin theory perspective. Guided by higher-spin constraints and classical-limit analysis, I will propose Compton amplitudes relevant for root-Kerr and Kerr to all orders in spin, and discuss their relation to gravitational-wave scattering on Kerr background, as described by black-hole perturbation theory.

**28 November 2023, 14:30**

In this seminar I will discuss how Exceptional field theory provides us with a natural framework to study AdS vacua and their CFT duals. I will start with a review of consistent truncations and their construction in ExFT, I will then describe two recent examples. In the first we constructed a new consistent truncation of type IIB supergravity on S^3xS^3xS^1. We then found several families of AdS3 vacua preserving various amounts of supersymmetry in 3 dimensions and uplifted the solutions to 10 d. In the second example we found a domain wall solution interpolating between the squashed and round S^7 vacua of 11 d supergravity. We then used the machinery of KK spectrometry to compute the quadratic couplings of fluctuations along the flow.

**21 November 2023, 15:00**

Over the past few years, the importance of chaos in the physics of quantum black holes has become clear. This is particularly well understood in two-dimensional gravity, where the boundary system is quantum mechanics. Quantum chaos is well understood in quantum mechanics, going back several decades to the work of Wigner, in terms of random matrix universality: the statistical spectral correlations of a chaotic hamiltonian are indistinguishable from those of a random matrix drawn from the appropriate ensemble. Quantum chaos is much less understood in quantum (and conformal) field theories, which appear in top-down realizations of AdS/CFT. What is the right ensemble of theories to draw from in the case of field theories, similar to the random matrix ensembles of Wigner? In this talk, I will review progress on this front, and explain how to incorporate the many CFT constraints into a framework of ensemble of CFTs.

**14 November 2023, 14:30**

Recently, there has been considerable interest in quantum field theories in two dimensions deformed by the irrelevant “TTbar” operator defined by the determinant of the stress-energy tensor. TTbar-like flows have also been shown to characterise effective field theories in higher dimensions. In this talk, I will review part of this research topic and describe results on TTbar deformation of supersymmetric theories, the role of TTbar-like flows for theories of non-linear electrodynamics in D=3,4, and the definition of a new (classically) marginal Root-TTbar deformation in 2D.

**07 November 2023, 14:30**

In this talk, I will review key ingredients used to construct off-shell higher-derivative invariants in (gauged) supergravity theories. The construction is based on an interplay between the superconformal tensor calculus, the superform approach to construct supersymmetric invariants, and novel off-shell superspace techniques. I will discuss how to obtain curvature-squared (four-derivative) invariants for (gauged) minimal supergravities in five (5D) and six (6D) dimensions, including the Gauss-Bonnet invariant, which is linked to the description of alpha'-corrections to the low-energy limit of compactified string theory. Time permitting, I will review how to obtain the two 6D N=(1,0) and single 6D N=(2,0) (six-derivative) conformal supergravity actions that describe type B anomalies of six-dimensional conformal field theories.

**06 November 2023, 14:30**

Characterizing vacua is one of the first targets when studying a physical system. In string theory, vacua near boundaries of moduli spaces have distinguished properties, which are related to their underlying geometry in a simple way. This is the essence of the swampland distance conjecture. I will extend these ideas to a notion of geometry for discrete sets of isolated vacua, which ought to arise when moduli are stabilized. To this end, geodesics in moduli space are "discretized" by domain walls interpolating between isolated vacua. This picture is connected to renormalization group flows and the information metric via holography, and provides a framework in which geometric properties of the string landscape and constraints on effective field theories can be studied in more realistic settings.

**24 October 2023, 14:30**

I will present our effort to analytically obtain the 1-point functions of chiral operators in N=2 gauge theories in four dimensions, when the theory is placed in the upper half-plane with 1/2-BPS boundary conditions. I will discuss such boundary conditions, along with the complications, and their solutions, for obtaining exact results via localization. As a non-trivial example, I will consider a bulk U(1) theory interacting with the boundary. A closed formula for its 1-point functions will be presented, together with the SL(2,Z)'s action in this set up and, finally, consistency checks also up to non-perturbative regimes (both analytically and via Padé resummations).

**17 October 2023, 15:00**