Novel critical phenomena in compressible polar active fluids: A functional renormalization group approach

TL;DR

This paper employs functional renormalization group techniques to discover and analyze new critical phenomena in compressible polar active fluids, extending understanding beyond previous incompressible models and one-loop approximations.

Contribution

It introduces a novel application of functional renormalization group methods to compressible polar active fluids, revealing new universality classes and critical exponents beyond one-loop level.

Findings

Identified three new universality classes in compressible polar active fluids.

Calculated critical exponents beyond the one-loop approximation.

Quantified scaling behavior near the upper critical dimension d_c=6.

Abstract

Active matter is not only relevant to living matter and diverse nonequilibrium systems, but also constitutes a fertile ground for novel physics. Indeed, dynamic renormalization group (DRG) analyses have uncovered many new universality classes (UCs) in polar active fluids - an archetype of active matter systems. However, due to the inherent technical difficulties in the DRG methodology, almost all previous studies have been restricted to polar active fluids in the incompressible or infinitely compressible (i.e., Malthusian) limits, and, when the $\epsilon$-expansion was used in conjunction, to the one-loop level. Here, we use functional renormalization group methods to bypass some of these difficulties and unveil for the first time novel critical behavior in compressible polar active fluids, and calculate the corresponding critical exponents beyond the one-loop level. Specifically, focusing on a multicritical region of the system, we find three novel UCs and quantify their associate scaling behavior near the upper critical dimension $d_c = 6$.