Non-Perturbative Dynamical Effects in Nearly Scale Invariant Systems: The Action of Breaking Scale Invariance

TL;DR

This paper develops a formalism to understand how breaking scale invariance non-perturbatively affects the long-term dynamics of non-relativistic quantum systems, with applications to two-body and impurity problems.

Contribution

It introduces a general approach to categorize non-perturbative effects of broken scale invariance in non-equilibrium quantum dynamics, applicable to various interaction strengths.

Findings

Deviations from the fixed point cause non-perturbative effects in long-time dynamics.

Presence of a log-periodic beat in the dynamics near the resonant fixed point.

Beat frequency depends on microscopic system parameters.

Abstract

In this work we develop a general formalism that categorizes the action of broken scale invariance on the non-equilibrium dynamics of non-relativistic quantum systems. This approach is equally applicable to both strongly and weakly interacting systems. We show that any small deviation from the strongly interacting fixed point, in three spatial dimensions, leads to non-pertubative effects in the long time dynamics, dramatically altering the dynamics observed at the scale invariant fixed point. As a concrete example, we apply this approach to the non-equilibrium dynamics for the interacting two-body problem, and for a non-interacting quantum gas in the presence of an impurity, both in three spatial dimensions. Slightly away from the resonantly-interacting scale invariant fixed point, we show that the dynamics are altered by a non-perturbative log-periodic beat. The presence of the beat depends only on deviating from the resonant fixed point, while the frequency depends on the microscopic parameters of the system.