Heterogeneous mean-field theory for two-species symbiotic processes on networks

TL;DR

This paper develops a heterogeneous mean-field theory to analyze the phase transitions of a two-species symbiotic contact process on networks, revealing how network heterogeneity influences bistability and transition nature.

Contribution

The study introduces a heterogeneity-aware mean-field approach for the 2SCP, providing new insights into phase transition behaviors on complex networks with power-law degree distributions.

Findings

Bistability region shrinks with increased heterogeneity.

Pseudo discontinuous transition can become continuous in the thermodynamic limit.

Theoretical predictions are validated by numerical simulations.

Abstract

A simple model to study cooperation is the two-species symbiotic contact process (2SCP), in which two different species spread on a graph and interact by a reduced death rate if both occupy the same vertex, representing a symbiotic interaction. The 2SCP is known to exhibit a complex behavior with a rich phase diagram, including continuous and discontinuous transitions between the active phase and extinction. In this work, we advance the understanding of the phase transition of the 2SCP on uncorrelated networks by developing a heterogeneous mean-field (HMF) theory, in which the heterogeneity of contacts is explicitly reckoned. The HMF theory for networks with power-law degree distributions shows that the region of bistability (active and inactive phases) in the phase diagram shrinks as the heterogeneity level is increased by reducing the degree exponent. Finite-size analysis reveals a complex behavior where a pseudo discontinuous transition at a finite-size can be converted into a continuous one in the thermodynamic limit, depending on degree exponent and symbiotic coupling. The theoretical results are supported by extensive numerical simulations.