Phase transitions on a class of generalized Vicsek-like models of collective motion

TL;DR

This paper generalizes the Vicsek model of collective motion by introducing arbitrary angular noise distributions, revealing how different noise types influence the nature of phase transitions in systems of self-propelled particles.

Contribution

It proposes a unified formalism for Vicsek-like models with multiplicative noise, deriving new models with Gaussian-based distributions, and analyzes how noise distribution affects phase transition order.

Findings

Phase transition type depends on noise distribution.

Hybrid scaling observed for vectorial and wrapped Gaussian noise.

Discontinuous transitions occur with short-range interactions.

Abstract

Systems composed of interacting self-propelled particles (SPPs) display different forms of order-disorder phase transitions relevant to collective motion. In this paper we propose a generalization of the Vicsek model characterized by an angular noise term following an arbitrary probability density function, which might depend on the state of the system and thus have a multiplicative character. We show that the well established vectorial Vicsek model can be expressed in this general formalism by deriving the corresponding angular probability density function, as well as we propose two new multiplicative models consisting on a bivariate Gaussian and a wrapped Gaussian distributions. With the proposed formalism, the mean-field system can be solved using the mean resultant length of the angular stochastic term. Accordingly, when the SPPs interact globally, the character of the phase transition depends on the choice of the noise distribution, being first-order with an hybrid scaling for the vectorial and wrapped Gaussian distributions, and second order for the bivariate Gaussian distribution. Numerical simulations reveal that this scenario also holds when the interactions among SPPs are given by a static complex network. On the other hand, using spatial short-range interactions displays, in all the considered instances, a discontinuous transition with a coexistence region, consistent with the original formulation of the Vicsek model.