Abstract

We describe the application of pseudo-spectral methods to problems of holographic thermal quenches of relevant couplings in strongly coupled gauge theories. We focus on quenches of a fermionic mass term in a strongly coupled N=4 supersymmetric Yang-Mills plasma, and the subsequent equilibration of the system. From the dual gravitational perspective, we study the gravitational collapse of a massive scalar field in asymptotically anti-de Sitter geometry with a prescribed boundary condition for its non-normalizable mode. Access to the full background geometry of the gravitational collapse allows for the study of nonlocal probes of the thermalization process. We discuss the evolution of the apparent and the event horizons, the two-point correlation functions of operators of large conformal dimensions, and the evolution of the entanglement entropy of the system. We compare the thermalization process from the viewpoint of local (the one-point) correlation functions and these nonlocal probes, finding that the thermalization time as measured by the probes is length dependent, and approaches the thermalization time of the one-point function for longer probes. We further discuss how the different energy scales of the problem contribute to its thermalization.

Highlights

  • Quantum quenches are processes where an isolated system is driven to a far-fromequilibrium state by rapidly varying some control parameters

  • Access to the full background geometry of the gravitational collapse allows for the study of nonlocal probes of the thermalization process

  • The main challenge is that gravitational simulations in asymptotically Minkowski spacetimes mostly have a compact physical dependence domain; on the contrary, in AdS, control over the whole spacetime, and especially near the boundary is crucial. The latter is emphasized in problems related to holographic quenches, where the temporal history of a quantum gauge theory coupling is encoded as a non-normalizable component of the gravitationally dual bulk scalar field near the boundary

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Summary

Introduction

Quantum quenches are processes where an isolated system is driven to a far-fromequilibrium state by rapidly varying some control parameters. In an ongoing research program including [51, 52] and [53], we study the response of a strongly coupled N = 4 supersymmetric Yang-Mills thermal plasma, quenched by a relevant operator, using the holographic duality Having previously studied such quenches, we apply more powerful numerical techniques to find the full time-dependent profiles of the perturbations of the metric and scalar field in the dual AdS spacetime. This allows us to utilize nonlocal probes such as two-point functions and entanglement entropy to better understand thermalization at various distance scales. This will serve as a prelude to the new solution of the full non-perturbative backreaction of the scalar field on the AdS-black brane geometry

The physical setup
Dimensionless coordinates
Leading-order backreaction
Rescaling the parameters
Probes of thermalization
Evolution of the apparent and event horizons
Analytic expression for the correlator
Numerical calculation of the perturbed two-point function
Analytic expression for the entanglement entropy
Contribution from surface perturbation
Regularization of the entanglement entropy
Numerical calculation of the entanglement entropy
Scaling of the thermalized correlator and entropy
Thermalization
Thermalization times of the entanglement entropy and two-point correlator
Equilibration of the correlator and entropy profiles
Equilibration profile of the scalar field and its stress-energy
Heuristics of thermalization
Conclusion
Definition and solution of fields in perturbative regime
Numerical implementation
Convergence tests
Findings
Limit of abrupt quenches

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