Abstract
We study gravity wave production and baryogenesis at the electroweak phase transition, in a real singlet scalar extension of the Standard Model, including vector-like top partners to generate the CP violation needed for electroweak baryogenesis (EWBG). The singlet makes the phase transition strongly first-order through its coupling to the Higgs boson, and it spontaneously breaks CP invariance through a dimension-5 contribution to the top quark mass term, generated by integrating out the heavy top quark partners. We improve on previous studies by incorporating updated transport equations, compatible with large bubble wall velocities. The wall speed and thickness are computed directly from the microphysical parameters rather than treating them as free parameters, allowing for a first-principles computation of the baryon asymmetry. The size of the CP-violating dimension-5 operator needed for EWBG is constrained by collider, electroweak precision, and renormalization group running constraints. We identify regions of parameter space that can produce the observed baryon asymmetry or observable gravitational (GW) wave signals. Contrary to standard lore, we find that for strong deflagrations, the efficiencies of large baryon asymmetry production and strong GW signals can be positively correlated. However we find the overall likelihood of observably large GW signals to be smaller than estimated in previous studies. In particular, only detonation-type transitions are predicted to produce observably large gravitational waves.
Highlights
Phase transitions in the early Universe provide an opportunity for probing physics at high scales through cosmological observables, in particular, if the transition is first order
In this work we have taken a first step toward making complete predictions for baryogenesis and gravity waves from a first-order electroweak phase transition, starting from a renormalizable Lagrangian that gives rise to the effective operator needed for CP violation
This is in contrast to previous studies in which quantities like the bubble wall velocity or thickness were treated as free parameters, instead of being derived from the microphysical input parameters as we have done here
Summary
Phase transitions in the early Universe provide an opportunity for probing physics at high scales through cosmological observables, in particular, if the transition is first order. [65,66] that do not suffer from the subsonic limitation We use these in the present work in order to fully explore the parameter space, where high vw can be favorable to observable GWs, and compatible with EWBG. III with a brief description of our methodology for finding the high-temperature firstorder phase transitions and characterizing their strength We present the results of a Monte Carlo exploration of the model parameter space with respect to these observables in Sec. VI, with emphasis on the interplay between successful EWBG and potentially observable GWs. Conclusions are given in Sec. VII, followed by several Appendixes containing details about construction of the finite-temperature effective potential, solving junction conditions for the phase transition boundaries, and predicting GW production
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