# Feynman-Vernon model of a moving thermal environment

## TL;DR

This paper extends the Feynman-Vernon model to include a thermal environment moving with velocity, deriving the Langevin equation and influence functional for a Brownian particle in such a setting, relevant for vortex motion in superfluids.

## Contribution

It introduces a generalized oscillator model for a Brownian particle in a moving thermal environment, incorporating space-time invariance and deriving related stochastic equations.

## Key findings

- Derived the Langevin equation for a moving environment
- Formulated the influence functional for the generalized model
- Connected the model to vortex motion in superfluids

## Abstract

This paper reviews the formulation of the Feynman-Vernon model of linear dissipative systems for a standard Brownian particle moving in an external potential $V(x,t)$ and introduces the formulation of a generalized oscillator model of a Brownian particle coupled to a thermal environment moving with a given velocity $v_{env}$. Diffusion processes in a moving environment are of interest e.g. in the study of the motion of vortices in superfluids. The starting point of the paper is the formulation of the oscillator model that takes into account space and time invariance of a thermal environment [M. Patriarca, Statistical correlations in the oscillator model of quantum Brownian motion, Il Nuovo Cimento B, 111(1), 61-72 (1996), doi: 10.1007/BF02726201, arXiv:1801.02429], which has the property of being finite and consistent with the classical limit. The Langevin equation and the influence functional for a Brownian particle in a moving environment are derived.