Nico Yunes on “A square peg in a circular hole, and other bad physics puns”
Abstract: I will discuss the mathematical construction of classical black hole solutions with asymptotically flat boundary conditions (no ADS, sorry) in modified theories of gravity that are inspired by quantum field theory, effective field theory and quantum gravity ideas. If I have enough time, I will then also talk about the properties of some of these solutions, and signatures that they may leave on astrophysical observables.
Helvi Witek on "The adventures of black holes: the case of quadratic gravity"
Abstract: With the advent of gravitational wave astronomy we are now in a perfect position to confront the multitude of beyond-GR theories, typically invoked to connect to quantum gravity paradigms, with actual observations in the strong-field regime of gravity. A necessary ingredient to do so, either via theory-specific tests or to guide parametrized approaches, are theoretical predictions of the (gravitational) radiation emitted by compact binaries in extensions of general relativity. In this talk I will present recent results on modelling black hole binaries in scalar Gauss-Bonnet gravity, a well-motivated theory that involves higher-curvature corrections to Einstein's equations. As black holes in this theory can acquire scalar hair, binaries thereof yield new phenomena such as additional scalar radiation, dephasing of the gravitational wave signal and, possibly most excitingly, dynamical de-scalarization during the merger.
Rob Leigh on "Holography with NUT charge”
Abstract: I will describe some recent and on-going work on holography in black hole geometries that are asymptotically locally anti-deSitter, particularly those carrying NUT charge. In the past few years, the significance of the corresponding Misner string singularities that appear in standard coordinizations has been appreciated in the context of black hole thermodynamics. A central issue is the physicality of the Misner string, that is if it preserves or violates the analogue of Dirac quantization conditions. Since in this case the quantization condition is on the frequency of fluctuations, the issue has an impact on important physical aspects of these black holes such as the nature of quasi-normal modes and the corresponding dissipation from the perspective of the dual boundary theory. Here we show that dissipation relies on the physicality of the Misner strings, and we will confront holography directly in the Lorentzian theory. Taub-NUT/BOLT solutions enjoy a large isometry algebra which allows us to study carefully solutions of the bulk problem, with perhaps surprising results — the solutions fall into non-unitary, infinite dimensional representations of the (complexified) isometry algebra.
Tom Faulker on “Bulk reconstruction or: How to tell if Schrödinger’s cat is dead or alive behind the horizon of an old black hole”
Abstract: I will discuss various approaches to the problem of bulk reconstruction in AdS/CFT. This problem has recently been more directly connected to the black hole information paradox and I will review this connection.
Gabriele LaNave on “Black hole evaporation and reconstruction in multi-boundary holographic models"
Abstract: Recently, Harlow et al. have proposed a holographic model of evaporation, the multi-boundary wormhole ‘octopus’ (and the related concepts of entanglement islands [29] and replica wormholes [16, 22]). This is basically a model in AdS3 /CFT2 where the boundary theory is obtained by gluing tentacles (like pairs of pants) onto a main Riemann surface body, which is interpreted as a model of evaporation (via radiating tiny black holes). By increasing the number of attached pairs of pants, one realizes a tension between the area of the HRT surface of the original blackhole and that of the ‘radiated’ blackholes. This tension is such that it reproduces the trend of the Page curve, albeit in discrete time. We will discuss a proposal of reconstruction using Tomita theory in this context, analogous to the one in the context of a double trace deformation of BTZ. One of the main technical issues is that in this context one does not have access to exact wedge regions to localize the algebras. Nonetheless we propose that it is possible to make the sequence of inclusions of algebras as sets into a sequence of approximate modular inclusions, making use of a certain Gromov-Haudorff distance to induce a notion of proximity of the algebras.