Talks


July 3 (Mon) 

Time: 10:30 - 11:15

Title: Higher-derivative corrections to BPS AdS_5 black holes and their holographic match  (slide) 

Abstract: The index of four-dimensional N=1 SCFT’s in a Cardy-like regime provides a microscopic derivation of the entropy of supersymmetric black holes in AdS_5, both at leading and subleading orders in the large-N expansion. After reviewing how the SCFT prediction is obtained, I will discuss how it is matched in gauged supergravity with higher-derivative corrections. The expression for the entropy as a function of the conserved charges is obtained in two different ways: by Legendre-transforming the on-shell action, and by a direct evaluation of Wald’s formula in the corrected near-horizon geometry. Along the way, I will emphasize the crucial role played by anomalies and I will discuss the issues that arise when dealing with higher-derivative terms in this context.


Time: 11:45 -15:00

Title: Quantum Corrections to near-extremal black hole thermodynamics ( slide )

Abstract: We consider a spherically symmetric near-extremal black hole in 4D Einstein-Maxwell theory, which is a very small temperature deviation of an extremal (zero-temperature) black hole. In such low temperatures, the quantum corrections become large enough to cause a breakdown of semiclassical physics. These result in logarithm of temperature corrections in thermodynamic entropy. We compute these corrections from the one-loop Euclidean path integral on the near-horizon region of near-extremal background. To compute the one-loop determinant, we invoke first-order perturbation theory, exploiting the enhanced symmetries of the near-horizon region of an extremal black hole.

Time: 16:00-17:15

Title: The endpoint of Kerr-AdS instability ( slide )

Abstract: Kerr black holes in AdS suffer from super-radiant instabilities at certain charges. We discuss the "endpoints" of the unstable black holes from thermodynamic and dynamical perspectives.

July 3(Tue)

Time: 10:00-11:15

Title: Black Holes in Quantum Mechanics  ( slide )

Abstract: I will motivate and study a holographic duality between on one hand the superconformal quantum mechanics of Yang-Mills instantons, and on the other, M-theory on a particular background. I will explain how to construct black hole solutions in the bulk theory, which are examples of “ultra-spinning” black holes. Through an asymptotic study of the superconformal index in the supergravity regime, I will provide a precise microstate counting for those black holes that are supersymmetric. Finally, I will discuss the relation of conformal quantum mechanics and ultra-spinning black holes to notions of holomorphic factorisation and gravitational blocks, for holographic CFTs in four and six dimensions.


Time: 11:15-12:30

Title: Giant graviton expansions for orbifolds and orientifolds. ( slide )

Abstract: We study giant graviton expansions of the superconformal index of 4d orbifold/orientifold theories. In general, a giant graviton expansion is given as a multiple sum over wrapping numbers, but it was found by Gaiotto and Lee that for N=4 SYM it can be reduced to a simple sum. We find in many examples of orbifold and orientifold theories such reduction occurs, and theories defined with different orbifold/orientifold projections are connected by giant graviton expansions.


Time: 14:00-15:15

Title: Black hole microstates from N=4 SYM ( slide )

Abstract:  I will talk about the cohomology of local BPS operators in N=4 Yang-Mills theory. We will see an infinite tower of non-graviton cohomologies in the SU(2) theory and discuss to what extent they simulate quantum black holes. We will find signals for partial no-hair behaviors by showing that certain gravitons are forbidden to dress these cohomologies. This is in qualitative agreement with the perturbative hairs allowed around black holes, which also leads us to a natural setup to construct hairy BPS black holes. These cohomologies are simpler to study in the BMN matrix model truncation of the classical field theory.


Time: 16:00- 18:00

July 4(Wed)

Time: 10:00-11:15

Title: Logarithmic Correction to the Gravitational Path Integral around Asymptotically Euclidean AdS4  (slide)

Abstract:  I will discuss a logarithmic correction to the gravitational path integral around asymptotically Euclidean AdS4 backgrounds that arise from the compactification of string/M-theory. The heat kernel method will be utilized, which divides the logarithmic correction into local and non-local contributions. The local contribution is determined by the 4th Seeley-DeWitt (SDW) coefficient, computed for generic massive fields with spins of 0, 1/2, 1, 3/2, and 2 on Einstein backgrounds by introducing Stueckelberg fields. On the other hand, the non-local contribution is influenced by the number of zero modes present on a given external geometry, which we have carefully examined in a couple of examples. Additionally, I will explore how the topological logarithmic correction to a dual CFT partition function constrains the 4th SDW coefficient for the Kaluza-Klein spectrum on Einstein-Maxwell backgrounds through holography. Finally, I will present an intriguing puzzle and discuss the related physics involved in reproducing the logarithmic correction to a CFT partition function from a dual gravitational path integral.


Time: 11:15-12:30

Title: AdS Black Hole Entropy and Cardy(-Like) Formulae ( silde )

Abstract: Since the seminal work by Strominger and Vafa, it has been found in many cases that the black hole entropy can be computed by applying the Cardy formula to a specific 2d CFT. In the last few years, the AdS/CFT correspondence started playing a role in computing higher-dimensional asymptotically AdS black hole entropy. However, the Cardy formula did not initially manifest in this new picture. We will demonstrate in this talk that the AdS black hole entropy can also be obtained from the two-dimensional Cardy formula and its higher-dimensional counterpart. In particular, despite the absence of conformal anomaly in odd dimensions, we consider 3d N=2 A-twisted partition functions and find some universal Cardy-like behavior. Consequently, we can compute the entropies of several asymptotically AdS_4 BPS black holes using a 3d Cardy-like formula. This talk is based on 2005.10251, 2106.09730, and 2306.05462.


Time: 14:00- 15:00 , 15:30-16:30

Title: Interpreting quantum mechanics in terms of classical processes


July 5(Thus)

Time: 10:30-11:45

Title:  Probing Supersymmetric Black Holes with Surface Defects ( silde )

Abstract: Supersymmetric black holes in Anti de-Sitter space have recently been shown to have a large number of exactly degenerate microstates, and it is an open problem to probe and ultimately distinguish these microstates in terms of the bulk degrees of freedom. In the first part of the talk, we will review how AdS5 black hole microstates may be reliably counted in the dual N=4 SYM theory using the 1/16 BPS superconformal index and how this result is reproduced by the bulk gravitational path integral in the near BPS / N=2 super JT gravity limit. This perspective also suggests a "mass gap" between BPS and near-BPS quantum black holes.

With the goal of understanding more detailed properties involving the BPS black holes using the bulk description, we will turn to the question of whether there are supersymmetric probes of the black hole which have an exact field theory dual. We find one such candidate is the superconformal index with the insertion of a Gukov-Witten surface operator of N=4 SYM, dual to a D3 brane which wraps the AdS5 black hole horizon. We find a saddle with a large N growth which can be exactly matched to the probe brane action. In addition to detecting the familiar deconfinement transition associated to the dominance of the bulk black hole saddle, this provides an example of a system in which a black hole interacts with other degrees of freedom which has a microscopic description.


Time: 13:45-15:00

Title: Supersymmetry and Localization on Euclidean AdS_2  ( slide )

Abstract: The validity of generic quantum studies of supersymmetric theories on euclidean AdS{_2} is questionable if one uses the existing standard normalizable bases. This is due to the fact that the standard bases are incompatible with supersymmetry. We first demonstrate the root of the problem and construct a ``supersymmetric Hilbert" space that not only cures the aforementioned problem, but also has an additional advantage of not allowing fermionic zero modes in the physical spectrum. 

We then delve deeper and use supersymmetric localization to study the partition function of N=(2,2) theory on euclidean AdS{_2}. The technique of localization itself is subtle on non-compact spaces with boundaries, and along the way, we resolve a few existing subtleties, viz., imposition of supersymmetric asymptotic boundary conditions, presence of fermion zero modes, proper definition of equivariant supercharge and ambiguities in the index expansion at fixed points of the U(1) group action on the manifold. Hopefully, this is a step forward in properly defining supersymmetric localization on non-compact spaces with boundaries.



Time: 16:00-17:15

Title:  Krylov complexity in the IP matrix model (  slide )

Abstract: The IP matrix model is a simple large N quantum mechanical model made up of an adjoint harmonic oscillator plus a fundamental harmonic oscillator. It is a model introduced previously as a toy model of the gauge theory dual of an AdS black hole. In the large N limit, one can solve the Schwinger-Dyson equation for the fundamental correlator, and at sufficiently high temperature, this model shows key signatures of thermalization and information loss; the correlator decay exponentially in time, and the spectral density becomes continuous and gapless. We study the Lanczos coefficients bn in this model and at sufficiently high temperature, it grows linearly in n with logarithmic corrections, which is one of the fastest growth under certain conditions. As a result, the Krylov complexity grows exponentially in time as 〜 \exp(O(√t) ). These results indicate that the IP model at sufficiently high temperature is chaotic.

July 6(Fri)

Time: 10:30-11:45

Title: The double scaled SYK model and non-commutative spacetime ( slide )

Abstract: TBA


Time: 13:45-15:00

Titile: The Crossed Product from a Holographic Quantum Error-Correcting Code ( silde )

Abstract: Recently, the old observation that the generalised entropy of a horizon --- the sum of the area and the entropy of exterior fields --- is better defined than either of the objects that make it up has been put on firmer footing by Witten et al. The main observation is that including fluctuations in the ADM charges in the algebra of bulk matter fields changes the type of algebra from type III_1 --- which doesn't have an entropy function --- to type II --- which does --- using the crossed product construction. We show that a holographic quantum error-correcting (QEC) code naturally has a structure analogous to the crossed product. Taking the encoded algebra to be type I, we construct two traces. In the limit where we take the encoded algebra towards a type III_1 algebra, one of the traces becomes that of a type II algebra. We are able to recover both type II_\infty --- relevant for black holes --- as well as type II_1 algebras -- relevant for cosmological horizons in de Sitter space --- by imposing different constraints on the area operator in the code. These results indicate that the holographic QEC code might be useful in contexts where the 'boundary' is actually an observer, like the static patch of de Sitter.