Abstract :  The inflationary scenario has become the standard

paradigm of early universe cosmology, but it is not
the only scenario which can explain the currently
available data on the large-scale structure of the
universe. I will compare inflation with two alternative
scenarios, the "Ekpyrotic bounce" scenario, and
"String Gas Cosmology". I will then argue that
there are severe obstacles to embed inflationary
cosmology into quantum gravity, and that the
alternative scenarios may be more promising"  

Zoom link: https://uky.zoom.us/j/94475622713

Recording: https://uky.zoom.us/rec/play/uZcvJryspjM3T4aRtASDVvIvW42-La6sh3IZ_aUEn0…

I will present a model of unitary black hole evaporation that eschews the use of quantum extremal surfaces in favor of regular Ryu-Takayanagi. This simplifies the arguments of recent derivations of the Page curve using the island formula and clarifies the relationship to quantum error-correction.

We argue that the SYK model leads to a three dimensional dual theory in a suitable background. At strong coupling, a Horava-Witten compactification of one of the dimensions reproduces the SYK spectrum, and a non-standard propagator of the 3D theory exactly reproduces the two point function of the bilocal fields. Furthermore, this three dimensional picture reproduces the leading finite coupling correction to the “zero mode” contribution. The space-time on which the bilocal fields live is not, however, the dual space-time in the sense of AdS/CFT duality – rather the bilocals are related to the dual fields by an integral transform.

Title: Gauss Bonnet Gravity and Singularity Crossing

Abstract: 

We study the effect of adding a Gauss Bonnet term to general relativity, in five dimensions, on modifying the singular behavior of certain gravitational solutions. These solutions are the Gauss Bonnet FRW cosmology and spherically symmetric Black hole solution. In these cases, we were able to show that nonspacelike geodesics can be extended across the singularities, which render these spacetimes geodesically complete. We check the consistency of these extensions with the field equations against the known Gauss Bonnet junction conditions.

Title: The Schwarzian and black hole physics

Abstract: In this talk, I will discuss the Schwarzian theory (relevant for low-energy SYK physics and Jackiw-Teitelboim gravity) from a 2d perspective. I will demonstrate how Schwarzian quantum mechanics is naturally embedded in 2d Liouville CFT. This perspective allows a direct computation of Schwarzian two- and four-point functions. Out-of-time ordered (OTO) four-point functions are also determined using the 2d R-matrix. The semi-classical limit of these expressions demonstrate various aspects of black holes, such as quasi-normal modes and eikonal shockwave expressions in the holographic bulk. In the end, I briefly discuss some generalizations to other theories. Mostly based on arXiv:1705.08408.

Path-Integral Complexity for Perturbed CFTs

Unitarity, causality and ghostbusting in non-equilibrium effective field theory

Abstract:

In this talk, I will discuss the dynamics of near-extremal Reissner-Nordstrom black holes in asymptotically four-dimensional Anti-de Sitter space (AdS4). In the spherically symmetric approximation and at low energies, the behaviour of the system in response to a probe scalar is well described by the Jackiw-Teitelboim (JT) model of gravity. In fact, this behaviour can be understood from symmetry considerations and arises due to the breaking of time reparametrisation invariance. The JT model has been analysed in considerable detail recently and related to the behaviour of the SYK model. The results that I will present indicate that features in these models which arise from symmetry considerations alone are more general and present quite universally in near-extremal black holes. 

Title: probing beyond ETH at large c

Abstract: Eigenstate thermalization hypothesis (ETH) is a phenomena often observed in systems characterized by quantum chaos. In this talk, we study ETH in 2d CFTs with large central charges. In particular, we focus on observables consisting of bilocal "probe" operators $\mathcal{O}_L(x)\mathcal{O}_L(0)$. A sharp feature of ETH in this context is the so-called "forbidden" singularities, arising in the thermodynamic limit $c\to\infty$. We explore their resolutions by finite $c$ effects, and analyze the associated non-perturbative phenomena. We also discuss some interesting similarities between the related real-time dynamics and the spectral form factors in both the SYK model and BTZ black holes.

There exists a class of ultralight Dark Matter (DM) models which could form a Bose-Einstein condensate (BEC) in the early universe and behave as a single coherent wave instead of individual particles in galaxies. We show that a generic BEC DM halo intervening along the line of sight of a gravitational wave (GW) signal could induce an observable change in the speed of GW, with the effective refractive index depending only on the mass and self-interaction of the constituent DM particles and the GW frequency. Hence, we propose to use the deviation in the speed of GW as a new probe of the BEC DM parameter space. With a multi-messenger approach to GW astronomy and/or with extended sensitivity to lower GW frequencies, the entire BEC DM parameter space can be effectively probed by our new method in the near future.