We have investigated the time evolution of (Renyi) entanglement entropies for a locally excited state defined by acting with a local operator. When the subsystem is given by a half of the total space, we have found that they approach finite constants in free field theories or solvable models. On the other hand, those entropies in holographic field theories logarithmically increase with t even at the late time. Thus they are expected to be a candidate which reveals the characteristic feature of holographic field theories. In the current works, we found that the entropies in free field theories are given by the probability with which the quasi-particle created by local operators located in the subsystem. We also introduce a toy model where a particle created by a local operator freely propagates. By using this model, we can reproduce the result which is obtained by the replica trick. I would like to explain the detail of our results as long as permitted.

We discuss information loss from black hole physics in AdS3, focusing on two sharp signatures infecting CFT2 correlators at large central charge c: 'forbidden singularities' arising from Euclidean-time periodicity due to the effective Hawking temperature, and late-time exponential decay in the Lorentzian region. We study an infinite class of examples where forbidden singularities can be resolved by non-perturbative effects at finite c, and we show that the resolution has certain universal features that also apply in the general case. Analytically continuing to the Lorentzian regime, we find that the non-perturbative effects that resolve forbidden singularities qualitatively change the behavior of correlators at times t∼SBH, the black hole entropy. This may resolve the exponential decay of correlators at late times in black hole backgrounds. By Borel resumming the 1/c expansion of exact examples, we explicitly identify 'information-restoring' effects from heavy states that should correspond to classical solutions in AdS3. Our results suggest a line of inquiry towards a more precise formulation of the gravitational path integral in AdS3.

A possible solution to the notorious sign problem for systems with non-zero chemical potential is to deform the integration region in the complex plane to a Lefschetz thimble. We introduce an easy to implement Monte Carlo algorithm to sample the dominant thimble, based on a contraction map on a thimble. We point out that manifolds other than Lefschetz thimble could be useful for numerical simulations. We describe a family of such manifolds, using the contraction map, that interpolate between the tangent space at one critical point (where the sign problem could be severe) and the union of relevant thimbles (where the sign problem is mild but a multimodal distribution function complicates the Monte Carlo sampling). We show how this works in a couple of models.

I will discuss nontrivial constraints on the spectrum and structure constants of 2D unitary CFTs from the associativity of OPE and modular invariance, and some implications for non-perturbative completions of gravity in AdS3.

Abstract: Axion stars, gravitationally bound states of low-energy axions, described by a field theory with potential energy f^2 m^2(1-Cos (A/f)) have a maximum mass allowed by gravitational stability. Weakly bound states obtaining this maximum mass have sufficiently large radii such that they are dilute, and as a result, they are well described by a leading-order expansion of the axion potential. Heavier states are susceptible to gravitational collapse. Inclusion of higher-order interactions, present in the full potential, can give qualitatively different results in the analysis of collapsing heavy states, as compared to the leading-order expansion. In this work, we find that collapsing axion stars are stabilized by repulsive interactions present in the full potential, providing evidence that such objects do not form black holes. These dense configurations, which are the endpoints of collapse, have extremely high binding energy, and as a result, quickly decay through number changing interactions.

On September 14, 2015, LIGO detectors picked up a gravitational wave signal coming from the merger of a binary black hole. This is the first direct detection of gravitational waves and the first observation of binary black hole and its merger. In this talk we will go over the key aspects of the discovery, and highlight some its implications for fundamental physics and astrophysics.