Quantum Fields and Strings

In holographic duality an eternal AdS black hole is described by two copies of the boundary CFT in the thermofield double state. We provide explicit constructions in the boundary theory of infalling time evolutions which can take bulk observers behind the horizon. The constructions also help to illuminate the boundary emergence of the black hole horizons, the interiors, and the associated causal structure. A key element is the emergence, in the large N limit of the boundary theory, of a type III1 von Neumann algebraic structure and the half-sided modular translation structure associated with it.

Zoom Link: https://pitp.zoom.us/j/99458239757?pwd=YTBRdXdwTjltMkdZc0Q4WW1jQjA3QT09

I will describe an approach to extracting the physical consequences of S-duality of four-dimensional N = 4 super Yang-Mills (SYM) and its string theory dual based on SL(2,Z) spectral theory. I will show that processing S-duality in this way leads to strong consequences for the CFT data, both perturbatively and non-perturbatively in all parameters. In large-N limits, I will argue for the existence and scaling of non-perturbative effects, both at large N and at strong 't Hooft coupling. An elegant benchmark for these techniques is a certain integrated stress-tensor multiplet four-point function, whose form I will elucidate. I will explain how the ensemble average of CFT observables over the N = 4 supersymmetric conformal manifold with respect to the Zamolodchikov measure is cleanly isolated by the spectral decomposition, and will show that the large-N limit of the ensemble average is equal to the strong-coupling limit of the observable in the planar theory, which is its value in type IIB supergravity on AdS_5 x S^5. This embeds an emergent averaged holographic duality within the conventional holographic paradigm.

Zoom link:  https://pitp.zoom.us/j/95197874062?pwd=QU4vbXNNeFVmS0hNbTVLL24wdDBndz09

Zoom link:  https://pitp.zoom.us/j/96132106700?pwd=L3ZMOXltZks4Y25abUl5TTdhZTVKUT09

Euclidean wormholes are exotic types of gravitational solutions that we still don't understand completely. In the first part of the talk, I will analyze asymptotically AdS wormhole solutions from a gravitational point of view. By studying correlation functions of local and non-local operators, the universal properties that any putative holographic dual should exhibit, become manifest. In the second part, I will describe some concrete field theoretic models (both effective and microscopic) that share these properties.

TTbar and JTbar - deformed CFTs provide an interesting example of non-local, yet UV-complete two-dimensional QFTs that are entirely solvable. I will start by showing that both classes of theories possess Virasoro x Virasoro or Virasoro- Kac- Moody x Virasoro - Kac- Moody symmetry. For the case of JTbar, I will discuss the classical realization of these symmetries in terms of field-dependent coordinate transformations and show how the associated generators can be used to define an analogue of "primary" operators in this non-local theory, whose correlation functions are entirely fixed in terms of those of the undeformed CFT. In particular, two and three-point functions are simply given by the corresponding momentum-space correlator in the undeformed CFT, with all dimensions replaced by particular momentum-dependent conformal dimensions. Interestingly, scattering amplitudes off the near-horizon of extremal black holes are known to take a strikingly similar form.

Several puzzles and issues in quantum gravity are related to the question of what type of high-energy information is actually available to low-energy observers. In this talk I will try to argue that the best description available to a low-energy observer is probably of a statistical nature. Such a statistical description naturally connects to e.g. the eigenstate thermalization hypothesis, and wormholes and the apparent lack of factorization. I will describe this statistical picture and the evidence we have for it, and what we could possibly learn from it. Partially based on work in progress.

Zoom Link: https://pitp.zoom.us/j/96646337719?pwd=UVRKN3Y4Q05xNXk1VExOenYwSFZvZz09

In this talk, we will discuss the late time behavior of out of time ordered correlators (OTOC). First part of the talk, we argue the nonlinear behavior of OTOC for general chaotic system is controlled by a Dray t’Hooft like action. Second part of the talk, we will discuss the late time nonperturbative effects in OTOC and its relation with random unitary behavior.

A salient feature of black holes near extremality is the appearance of an AdS$_2$ throat in their near-horizon geometry. Depending on the underlying theory, these AdS$_2$ throats may be unstable to fragmentation, wherein a single throat is instead replaced by a tree-like structure of branched AdS$_2$ throats. For Einstein-Maxwell theory, the underlying reason behind this instability is the existence of multi-centered configuration in the moduli space of black hole solutions at fixed total charge. Given the success of the Schwarzian/SYK paradigm for understanding a single AdS$_2$ it is time to revisit the fragmentation story. To build up intuition, I will present a model, studied in the statistical mechanics literature, that shares many features with SYK, including exact solvability at large-N and an emergent conformal symmetry that gets weakly broken in the UV. The novel feature of this model is the appearance of a spin glass phase at O(1) temperatures, which I will try to relate to the fragmentation story.

In this talk I will review work on `decomposition,' a property of 2d theories with 1-form symmetries and, more generally, d-dim'l theories with (d-1)-form symmetries. Decomposition is the observation that such quantum field theories are equivalent to ('decompose into’)  disjoint unions of other QFTs, known in this context as "universes.” Examples include two-dimensional gauge theories and orbifolds with matter invariant under a subgroup of the gauge group. Decomposition explains and relates several physical properties of these theories -- for example, restrictions on allowed instantons arise as a "multiverse interference effect" between contributions from constituent universes. First worked out in 2006 as part of efforts to understand string propagation on stacks, decomposition has been the driver of a number of developments since. In the first half of this talk, I will review decomposition; in the second half, I will focus on the recent application to anomaly resolution of Wang-Wen-Witten in two-dimensional orbifolds.

The quantization of a non-linear sigma model in 1+1 dimensional space-time, whose target space is equipped with a non positive definite metric is an interesting open problem having potential applications to string theory and Condensed Matter Physics. Perhaps the simplest example where it can be studied is the 2D Lorentzian black hole sigma model that was introduced by Witten in '91. The purpose of this talk is to discuss the results of  the paper arXiv:2010.10613. There it was found that the scaling limit of a certain spin chain, that lies within the integrability class of an inhomogeneous six-vertex model, is closely related to the Lorentzian black hole sigma model and its Euclidean version.

Zoom Link: https://pitp.zoom.us/j/91519988720?pwd=RTdrT1NWc3V0SXZVTGxETVBlTm5YUT09

Fractons are relatively new types of quasiparticles which have recently been inspiring activity within several branches of physics. I will offer some motivations and perspectives from quantum information theory, condensed matter physics, and high energy physics, focusing mainly on my work in the latter two subjects. This talk is primarily based on https://arxiv.org/abs/2108.08322 and a paper to appear shortly with Dominic Williamson.