Ground states and phase transitions for an aggregation model with fast diffusion on sphere

TL;DR

This paper analyzes a sphere-based free energy model combining fast diffusion entropy and nonlocal attraction, identifying phase transitions and ground states, including Dirac masses, through theoretical and numerical methods.

Contribution

It introduces a generalized free energy model with fast diffusion and nonlocal interactions, characterizing phase transitions and ground states on the sphere.

Findings

Different regimes yield qualitatively distinct equilibria.

Fast diffusion can lead to Dirac mass concentrations.

Numerical results support theoretical phase transition analysis.

Abstract

We consider a free energy on the sphere that contains an entropy associated to nonlinear fast diffusion, and a nonlocal interaction energy. The two components of the free energy compete with each other, as one favours spreading and the other promotes concentration, respectively. The model is a generalization of the Onsager free energy with dipolar potential, used to study polymer orientation. We study the global energy minimizers of the energy functional, and in particular the various phase transitions that occur with respect to the strength of the nonlocal attractive interactions. In the considered regime, diffusion reduces as the density increases, for which reason the global energy minimizers can contain Dirac mass concentrations. We identify various ranges of the fast diffusion exponent and of the interaction strength, which give qualitatively different equilibria and ground states. The theoretical results are supported by numerical illustrations.