# Influence functionals, decoherence and conformally coupled scalars

## TL;DR

This paper explores how conformally coupled scalar fields in modified gravity theories induce decoherence effects, deriving evolution equations for the reduced density matrix using influence functionals and applying them to atom-interferometry experiments.

## Contribution

It introduces a novel approach to derive evolution equations for the reduced density matrix in scalar-tensor theories, enabling analysis of decoherence effects in quantum experiments.

## Key findings

- Derived evolution equations for the reduced density matrix using influence functionals.
- Applied the framework to analyze decoherence in atom-interferometry experiments.
- Provided insights into the quantum effects of modified gravity theories.

## Abstract

Some of the simplest modifications to general relativity involve the coupling of additional scalar fields to the scalar curvature. By making a Weyl rescaling of the metric, these theories can be mapped to Einstein gravity with the additional scalar fields instead being coupled universally to matter. The resulting couplings to matter give rise to scalar fifth forces, which can evade the stringent constraints from local tests of gravity by means of so-called screening mechanisms. In this talk, we derive evolution equations for the matrix elements of the reduced density operator of a toy matter sector by means of the Feynman-Vernon influence functional. In particular, we employ a novel approach akin to the LSZ reduction more familiar to scattering-matrix theory. The resulting equations allow the analysis, for instance, of decoherence induced in atom-interferometry experiments by these classes of modified theories of gravity.