Voids in Coupled Scalar Field Cosmology

TL;DR

This paper investigates how coupled scalar field theories influence cosmic voids, showing they develop earlier, are larger, and have sharper boundaries compared to standard LCDM, offering new ways to test cosmological models.

Contribution

It provides the first detailed numerical analysis of void properties in coupled scalar field theories, highlighting their distinct effects on cosmic structure formation.

Findings

Voids form earlier and are larger in coupled scalar field models.

A greater fraction of space is under-dense in these models.

Void boundaries are sharper compared to LCDM.

Abstract

We study the properties of voids in two different types of coupled scalar field theories. Due to the fifth force produced by the scalar field coupling, the matter particles feel stronger attraction amongst each other and cluster more quickly than they do in the standard LCDM model. Consequently voids in the coupled scalar field theories start to develop earlier and end up bigger, which is confirmed by our numerical simulations. We find that a significantly larger portion of the whole space is under-densed in the coupled scalar field theories and there are more voids whose sizes exceed given thresholds. This is more prominent in early times because at later times the under-dense regions have already been evacuated in coupled scalar field theories and there is time for the LCDM model to catch up. The coupled scalar field theories also predict a sharper transition between voids and high density regions. All in all, the qualitative behaviour is different not only from the LCDM result, but also amongst specific coupled scalar field models, making voids a potential candidate to test alternative ideas about the cosmic structure formation.