Temperature and friction fluctuations inside a harmonic potential

TL;DR

This paper compares the effects of temperature versus friction fluctuations on a molecule's motion in a harmonic potential, revealing distinct statistical behaviors and stationary distributions for each interpretation.

Contribution

It introduces a detailed analysis of diffusivity fluctuations as temperature or friction variations, showing their different impacts on the process's statistical properties and stationary distributions.

Findings

Friction fluctuations lead to Gaussian stationary distributions.

Temperature fluctuations can produce Gaussian or generalized Laplace distributions.

The characteristic functions and limit behaviors differ significantly between the two interpretations.

Abstract

In this article we study the trapped motion of a molecule undergoing diffusivity fluctuations inside a harmonic potential. For the same diffusing-diffusivity process, we investigate two possible interpretations. Depending on whether diffusivity fluctuations are interpreted as temperature or friction fluctuations, we show that they display drastically different statistical properties inside the harmonic potential. We compute the characteristic function of the process under both types of interpretations and analyse their limit behavior. Based on the integral representations of the processes we compute the mean-squared displacement and the normalized excess kurtosis. In the long-time limit, we show for friction fluctuations that the probability density function (PDF) always converges to a Gaussian whereas in the case of temperature fluctuations the stationary PDF can display either Gaussian distribution or generalized Laplace (Bessel) distribution depending on the ratio between diffusivity and positional correlation times.