Gravitational waves from a very strong electroweak phase transition

TL;DR

This paper explores the generation of gravitational waves during a strong electroweak phase transition in extended Standard Model scenarios, assessing their detectability by future space-based interferometers like eLISA.

Contribution

It models bubble dynamics and gravitational wave production in strongly first-order electroweak phase transitions, identifying parameter regions with observable signals.

Findings

Gravitational waves from sound waves are typically dominant.

Models with heavy extra bosons yield stronger signals.

Detection prospects are better in non-runaway wall scenarios.

Abstract

We investigate the production of a stochastic background of gravitational waves in the electroweak phase transition. We consider extensions of the Standard Model which can give very strongly first-order phase transitions, such that the transition fronts either propagate as detonations or run away. To compute the bubble wall velocity, we estimate the friction with the plasma and take into account the hydrodynamics. We track the development of the phase transition up to the percolation time, and we calculate the gravitational wave spectrum generated by bubble collisions, magnetohydrodynamic turbulence, and sound waves. For the kinds of models we consider, we find parameter regions for which the gravitational waves are potentially observable at the planned space-based interferometer eLISA. In such cases, the signal from sound waves is generally dominant, while that from bubble collisions is the least significant of them. Since the sound waves and turbulence mechanisms are diminished for runaway walls, the models with the best prospects of detection at eLISA are those which do not have such solutions. In particular, we find that heavy extra bosons provide stronger gravitational wave signals than tree-level terms.