Gravitational shine of dark domain walls

TL;DR

This paper explores how dynamically induced domain walls with decreasing tension can generate distinctive gravitational wave signals, potentially detectable by future observatories, and discusses their connection to dark matter production mechanisms.

Contribution

It introduces a model where domain wall tension decreases over time, leading to unique gravitational wave spectra and links to dark matter production scenarios.

Findings

Gravitational wave spectrum from domain walls is distinct from other sources.

Detectable gravitational wave signals are possible if the domain field is feebly coupled.

Dark matter can be produced during phase transitions associated with domain wall formation or dissolution.

Abstract

Cosmic domain walls are harmless, provided that their tension decreases with expansion of the Universe. This setup can be realized, if the scale of spontaneous symmetry breaking is induced dynamically through the interaction with hot primordial plasma. In that case, the domain wall tension can attain large values in the early Universe without any conflict with observations. Owing to the large initial tension, these topological defects may serve as a powerful source of gravitational waves. We make a preliminary estimate of the gravitational wave spectrum and argue that it is distinct from the spectrum produced by other sources, in particular by domain walls of a constant tension. The resulting gravitational wave signal is in the range accessible by Einstein Telescope, DECIGO, TianQin, LISA, IPTA, or SKA, if the field constituting the domain walls is very feebly coupled with hot primordial plasma and has tiny self-interactions. In particular, one can consider this field for the role of Dark Matter. We discuss various Dark Matter production mechanisms and properties of the emitted gravitational waves associated with them. We find that the conventional freeze-out and freeze-in mechanisms lead to large and perhaps unobservable frequency of gravitational waves. However, the Dark Matter production is also possible at the second order phase transition leading to the domain wall formation or at the inverse phase transition, when the domain walls get dissolved eventually. In both cases, there is essentially no lower bound on the frequency of emitted gravitational waves.