Speaker
Description
Cosmological first-order phase transitions can generate stochastic gravitational wave backgrounds that provide a window into the early universe at the electroweak scale. The upcoming Laser Interferometer Space Antenna (LISA) will be sensitive to the mHz frequency band of these gravitational waves, providing a probe of physics beyond the Standard Model (BSM). Extracting the phase transition parameters and inferring the underlying BSM theory is a challenging task, as it requires comparing observations to theoretical predictions across a high-dimensional parameter space. However, running a full lattice simulation for each parameter point is prohibitively expensive.
We address this challenge using the Sound Shell Model, a computationally efficient semi-analytical framework that reproduces the results of lattice simulations for intermediate-strength transitions. We extend the Sound Shell Model by incorporating additional key physical effects, including variations in the sound speed that change the underlying bubble hydrodynamics, and thermal suppression of bubble nucleation and the finite lifetime of the acoustic source, which broaden the validity of the model across the parameter space.
These developments provide a fast and flexible framework for modeling stochastic gravitational wave signals from phase transitions. In this talk, I will show how this improved modeling changes the predictions for previously published benchmark models. We have implemented this modeling in the open-source utilities PTtools and PTPlot. This enables likelihood-based parameter inference with LISA, and direct experimental tests of BSM scenarios at the electroweak scale.
| Other topic / keywords: | phase transitions, LISA |
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