How robust are gravitational wave predictions from cosmological phase transitions?

TL;DR

This paper examines how the choice of transition temperature affects gravitational wave predictions from cosmological phase transitions, revealing significant variations especially in strongly supercooled cases and highlighting errors from common approximations.

Contribution

It systematically analyzes the impact of transition temperature choice and approximation methods on GW signal predictions, providing guidance for more accurate modeling.

Findings

Peak GW amplitude varies by a factor of a few to an order of magnitude depending on supercooling.

Using mean bubble separation can cause several orders of magnitude variation in amplitude.

Many approximations lead to at least 10% error, with some over an order of magnitude.

Abstract

Gravitational wave (GW) predictions of cosmological phase transitions are almost invariably evaluated at either the nucleation or percolation temperature. We investigate the effect of the transition temperature choice on GW predictions, for phase transitions with weak, intermediate and strong supercooling. We find that the peak amplitude of the GW signal varies by a factor of a few for weakly supercooled phase transitions, and by an order of magnitude for strongly supercooled phase transitions. The variation in amplitude for even weakly supercooled phase transitions can be several orders of magnitude if one uses the mean bubble separation, while the variation is milder if one uses the mean bubble radius instead. We also investigate the impact of various approximations used in GW predictions. Many of these approximations introduce at least a 10% error in the GW signal, with others introducing an error of over an order of magnitude.