Cosmological First-Order Vacuum Phase Transitions in an Expanding Anisotropic Universe

TL;DR

This study uses numerical simulations to explore how first-order vacuum phase transitions in an anisotropic universe affect cosmic anisotropy, considering different scalar field mass scales and their impact on the universe's evolution.

Contribution

It introduces a detailed numerical analysis of vacuum phase transitions in an anisotropic universe using Bianchi Type-I metric, highlighting the effects on anisotropy and phase transition completion.

Findings

Anisotropy from phase transitions depends on scalar field mass scale.

Successful phase transition completion is unaffected by neglecting cosmic expansion.

Event contribution to anisotropy varies with initial bubble population.

Abstract

We examine the anisotropy originated from a first-order vacuum phase transitions through three-dimensional numerical simulations. We apply Bianchi Type-I metric to our model that has one scalar field minimally coupled to the gravity. We calculate the time evolution of the energy density for the shear scalar and the directional Hubble parameters as well as the power spectra for the scalar field and the gravitational radiation although there are a number of caveats for the tensor perturbations in Bianchi Type-I universe. We run simulations with different mass scales of the scalar field, therefore, in addition to investigation of anisotropy via the shear scalar, we also determine at which mass scale the phase transition completes successfully, hence, neglecting the expansion of the Universe does not significantly affect the results. Finally, we showed that such an event may contribute to the total anisotropy depending on the mass scale of the scalar field and the initial population of nucleated bubbles.