A Dynamic Renormalization Group Study of Active Nematics

TL;DR

This paper uses dynamical renormalization group analysis to study the behavior of active nematics, revealing that nonlinearities are marginally irrelevant and that these systems exhibit quasi-long-range order similar to equilibrium nematics.

Contribution

It provides a systematic derivation of the coarse-grained equations for active nematics and shows the nonlinearities are marginally irrelevant, with a special limit related to the 2D stochastic Burgers equation.

Findings

Nonlinearities are marginally irrelevant in active nematics.

Active nematics exhibit quasi-long-range order similar to equilibrium systems.

A special parameter limit relates the system to the 2D stochastic Burgers equation.

Abstract

We carry out a systematic construction of the coarse-grained dynamical equation of motion for the orientational order parameter for a two-dimensional active nematic, that is a nonequilibrium steady state with uniaxial, apolar orientational order. Using the dynamical renormalization group, we show that the leading nonlinearities in this equation are marginally \textit{irrelevant}. We discover a special limit of parameters in which the equation of motion for the angle field of bears a close relation to the 2d stochastic Burgers equation. We find nevertheless that, unlike for the Burgers problem, the nonlinearity is marginally irrelevant even in this special limit, as a result of of a hidden fluctuation-dissipation relation. 2d active nematics therefore have quasi-long-range order, just like their equilibrium counterparts