Domain wall and isocurvature perturbation problems in a supersymmetric axion model

TL;DR

This paper investigates the cosmological issues of domain walls and isocurvature perturbations in a supersymmetric axion model, using lattice simulations to determine conditions avoiding domain wall formation.

Contribution

It demonstrates that in a SUSY axion model, domain walls are avoided if the initial PQ field value is below a certain threshold, addressing key cosmological problems.

Findings

Domain walls are not formed when initial PQ field < 10^3 times the symmetry breaking scale.

Large PQ field oscillations can lead to domain wall formation via parametric resonance.

Supersymmetric axion models can resolve cosmological domain wall problems under specific initial conditions.

Abstract

The axion causes two serious cosmological problems, domain wall and isocurvature perturbation problems. Linde pointed that the isocurvature perturbations are suppressed when the Peccei-Quinn (PQ) scalar field takes a large value $\sim M_{\text{pl}}$ (Planck scale) during inflation. In this case, however, the PQ field with large amplitude starts to oscillate after inflation and large fluctuations of the PQ field are produced through parametric resonance, which leads to the formation of domain walls. We consider a supersymmetric axion model and examine whether domain walls are formed by using lattice simulation. It is found that the domain wall problem does not appear in the SUSY axion model when the initial value of the PQ field is less than $10^{3}\times v$ where $v$ is the PQ symmetry breaking scale.