Biased Domain Walls and the Origin of Early Massive Structures

TL;DR

This paper models how biased domain walls from early universe phase transitions could have contributed significantly to early structure formation, potentially explaining observed mass excesses at high redshifts.

Contribution

It introduces a non-parametric analytical model to estimate decay energy and collapse rates of domain walls, highlighting the role of biased walls in early structure formation.

Findings

Biased domain walls can produce massive objects comparable to galaxy clusters.

Collapse of biased walls may explain mass excess at high redshift ($z \,\gtrsim\, 7$).

Standard domain walls have a subdominant role in structure formation.

Abstract

Discrete symmetry-breaking phase transitions in the early universe may have caused the formation of networks of sheet-like topological defects, usually referred to as domain walls, which separate regions that have settled into different vacuum states. Field theory simulations predict the successive collapse of increasingly larger domains, which could potentially leave observable imprints in present-day large-scale structures. We use a non-parametric analytical model to provide an estimate of the final decay energy of these walls and their associated collapse rate, as a function of redshift. The energy released by collapsing walls can act as a seed for density perturbations in the background matter field, influencing structure formation. We estimate the dependence of the current mass of the resulting non-linear objects on the collapse redshift and wall tension, showing that domain walls can contribute to the formation of objects as massive as present-day galaxy clusters. Still, we confirm that the contribution of standard domain walls to structure formation is subdominant. In contrast, biased domain walls - originating in models with an approximate (or biased) discrete symmetry breaking - generally face much less stringent constraints on their tension, which allows for significantly higher collapse energies. Based on our analysis, we are able to show that the collapse of such biased wall networks can provide a significant contribution to structure formation, and, in particular, a mass excess at $z \gtrsim 7$ as suggested by JWST data.