Gravitational Waves from Q-ball Formation

TL;DR

This paper investigates the potential detectability of gravitational waves generated by Q-ball formation in the early universe, considering dilution effects and finite temperature influences, and identifies conditions under which future detectors might observe these signals.

Contribution

It analyzes the conditions for detecting gravitational waves from Q-ball formation, incorporating dilution and temperature effects, and highlights a specific parameter region where detection is feasible.

Findings

Detectability of GWs depends on the dominance of thermal logarithmic potential.

GWs are detectable only in a small parameter space with specific potential dominance.

Detection of GWs could provide insights into early universe conditions and flat directions.

Abstract

We study the detectability of the gravitational waves (GWs) from the Q-ball formation associated with the Affleck-Dine (AD) mechanism, taking into account both of the dilution effect due to Q-ball domination and of finite temperature effects. The AD mechanism predicts the formation of non-topological solitons, Q-balls, from which GWs are generated. Q-balls with large conserved charge $Q$ can produce a large amount of GWs. On the other hand, the decay rate of such Q-balls is so small that they may dominate the energy density of the universe, which implies that GWs are significantly diluted and that their frequencies are redshifted during Q-ball dominated era. Thus, the detectability of the GWs associated with the formation of Q-balls is determined by these two competing effects. We find that there is a finite but small parameter region where such GWs may be detected by future detectors such as DECIGO or BBO, only in the case when the thermal logarithmic potential dominates the potential of the AD field. Otherwise GWs from Q-balls would not be detectable even by these futuristic detectors: $\Omega_{\rm GW}^0<10^{-21}$. Unfortunately, for such parameter region the present baryon asymmetry of the universe can hardly be explained unless one fine-tunes A-terms in the potential. However the detection of such a GW background may give us an information about the early universe, for example, it may suggest that the flat directions with $B-L=0$ are favored.