# Open quantum dynamics induced by light scalar fields

## TL;DR

This paper derives a master equation describing how a light scalar field environment affects quantum probe fields, including decoherence and diffusion, with implications for experimental detection and theoretical modeling.

## Contribution

It introduces a novel derivation of the open quantum dynamics influenced by light scalar fields using advanced quantum field theory techniques, accounting for non-Markovian effects and time-dependent renormalization.

## Key findings

- Master equation includes corrections to coherent dynamics, decoherence, and diffusion.
- Non-Markovian effects cause time-dependent modulation of vacuum counterterms.
- Time-dependent renormalization is necessary for cutoff-independent results.

## Abstract

We consider the impact of a weakly coupled environment comprising a light scalar field on the open dynamics of a quantum probe field, resulting in a master equation for the probe field that features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. The light scalar is assumed to couple to matter either through a nonminimal coupling to gravity or, equivalently, through a Higgs portal. Motivated by applications to experiments such as atom interferometry, we assume that the probe field can be initialized, by means of external driving, in a state that is not an eigenstate of the light scalar-field--probe system, and we derive the master equation for single-particle matrix elements of the reduced density operator of a toy model. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements. This derivation of the master equation requires techniques of non-equilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo field dynamics, used to motivate a method of Lehmann-Symanzik-Zimmermann-like reduction. In order to obtain cutoff-independent results for the probe-field dynamics, we find that it is necessary to use a time-dependent renormalization procedure. Specifically, we show that non-Markovian effects following a quench, namely the violation of time-translational invariance due to finite-time effects, lead to a time-dependent modulation of the usual vacuum counterterms.