Alexandre Belin, Jan de Boer, Pranjal Nayak, Julian Sonner
SciPost Phys. 12, 059 (2022) ·
published 11 February 2022

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We generalize the eigenstate thermalization hypothesis to systems with global symmetries. We present two versions, one with microscopic charge conservation and one with exponentially suppressed violations. They agree for correlation functions of simple operators, but differ in the variance of charged onepoint functions at finite temperature. We then apply these ideas to holography and to gravitational lowenergy effective theories with a global symmetry. We show that Euclidean wormholes predict a nonzero variance for charged onepoint functions, which is incompatible with microscopic charge conservation. This implies that global symmetries in quantum gravity must either be gauged or explicitly broken by nonperturbative effects.
SciPost Phys. 11, 034 (2021) ·
published 18 August 2021

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Quantum chaotic systems are often defined via the assertion that their
spectral statistics coincides with, or is well approximated by, random matrix
theory. In this paper we explain how the universal content of random matrix
theory emerges as the consequence of a simple symmetrybreaking principle and
its associated Goldstone modes. This allows us to write down an effectivefield
theory (EFT) description of quantum chaotic systems, which is able to control
the level statistics up to an accuracy ${\cal O} \left(e^{S} \right)$ with $S$
the entropy. We explain how the EFT description emerges from explicit
ensembles, using the example of a matrix model with arbitrary invariant
potential, but also when and how it applies to individual quantum systems,
without reference to an ensemble. Within AdS/CFT this gives a general framework
to express correlations between "different universes" and we explicitly
demonstrate the bulk realization of the EFT in minimal string theory where the
Goldstone modes are bound states of strings stretching between bulk spectral
branes. We discuss the construction of the EFT of quantum chaos also in higher
dimensional field theories, as applicable for example for higherdimensional
AdS/CFT dual pairs.
SciPost Phys. 7, 003 (2019) ·
published 4 July 2019

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We use the monodromy method to compute expectation values of an arbitrary
number of light operators in finitely excited ("heavy") eigenstates of
holographic 2D CFT. For eigenstates with scaling dimensions above the BTZ
threshold, these behave thermally up to small corrections, with an effective
temperature determined by the heavy state. Below the threshold we find
oscillatory and not decaying behavior. As an application of these results we
compute the expectation of the outoftime order arrangement of four light
operators in a heavy eigenstate, i.e. a sixpoint function. Above the threshold
we find maximally scrambling behavior with Lyapunov exponent $2\pi T_{\rm
eff}$. Below threshold we find that the eigenstate OTOC shows persistent
harmonic oscillations.