# Dynamical renormalization group approach to the collective behaviour of swarms

## TL;DR

This paper uses the dynamical renormalization group to analyze a model of natural swarms, revealing a crossover between conservative and dissipative fixed points, and showing that non-dissipative couplings better match experimental data.

## Contribution

It introduces a renormalization group analysis of a non-dissipative swarm model, identifying a crossover between fixed points and aligning theoretical predictions with experiments.

## Key findings

- Crossover between conservative and dissipative fixed points identified.
- In three dimensions, the critical exponent z=3/2 matches experimental data better.
- Non-dissipative couplings are essential for realistic swarm modeling.

## Abstract

We study the critical behaviour of a model with non-dissipative couplings aimed at describing the collective behaviour of natural swarms, using the dynamical renormalization group. At one loop, we find a crossover between a conservative yet unstable fixed point, characterized by a dynamical critical exponent $z=d/2$, and a dissipative stable fixed point with $z=2$, a result we confirm through numerical simulations. The crossover is regulated by a conservation length scale that is larger the smaller the effective friction, so that in finite-size biological systems with low dissipation, dynamics is ruled by the conservative fixed point. In three dimensions this mechanism gives $z=3/2$, a value significantly closer to the experimental result $z\approx 1$ than the value $z\approx 2$ found in fully dissipative models, either at or off equilibrium. This result indicates that non-dissipative dynamical couplings are necessary to develop a theory of natural swarms fully consistent with experiments