The role of noise and advection in absorbing state phase transitions

TL;DR

This paper investigates how noise and advection influence phase transitions in directed percolation, revealing that even minimal advection can alter universality classes and that noise form significantly impacts the phase diagram.

Contribution

It demonstrates that small advection velocities can change the universality class of directed percolation and explores how different noise dependencies modify the phase diagram and stability.

Findings

Small advection velocity changes the universality class.

Noise proportional to sqrt density creates a spinodal line.

Linear noise in density alters phase boundaries dramatically.

Abstract

We study the effect of advection and noise on the field theory for directed percolation (DP). We show that even a very small advective velocity is enough to change the universality class of the dynamic phase transition. When the noise is taken to be proportional to the square root of the population density, we find an additional nonequilibrium 'spinodal' line separating a region where an exponentially decreasing density is metastable, from another one in which it is unstable. If the noise is instead linear in the density, the phase diagram changes dramatically both quantitatively and qualitatively, and the spinodal line becomes a true phase boundary. We briefly discuss possible applications of our results to microbial sedimentation and population dynamics in rivers.