Abstract
An axion-like particle (ALP) offers a new direction in electroweak baryogenesis because the periodic nature enables it to trigger a strong first-order phase transition insensitively to the decay constant $f$. For $f$ much above TeV, the ALP-induced electroweak phase transition is approximately described by adiabatic processes, distinguishing our scenario for electroweak baryogenesis from the conventional ones. We show that, coupled to the electroweak anomaly, the ALP can naturally realize spontaneous electroweak baryogenesis to solve the matter-antimatter asymmetry problem for $f$ in the range between about $10^5$ GeV and $10^7$ GeV. In such an ALP window, the $CP$ violation for baryogenesis is totally free from the experimental constraints, especially from the recently improved limit on the electron electric dipole moment. Future searches for ALPs could probe our scenario while revealing the connection between electroweak symmetry breaking and baryogenesis.
Highlights
The observed matter-antimatter asymmetry in the Universe is one of the pieces of strong evidence for physics beyond the Standard Model (SM)
Viable electroweak baryogenesis (EWBG) is achievable in an extension of the SM in which the electroweak phase transition (EWPT) is sufficiently strong and CP violation is large during the phase transition
II, we show that a strong first-order phase transition is achievable in the Higgs potential modified by the axionlike particle (ALP) even in the weakly coupled regime with f much above TeV and discuss essential features of the ALP-induced EWPT
Summary
The observed matter-antimatter asymmetry in the Universe is one of the pieces of strong evidence for physics beyond the Standard Model (SM). [19,20], but mostly in the context of cold baryogenesis [21] Those models rely on efficient production of Higgs winding numbers, which could be achieved through a preheating stage with an inflaton coupled the Higgs sector [21], or a delayed first-order phase transition induced by conformal symmetry breaking and subsequent bubble collisions [22,23]. Such a violent environment can generate unstable Higgs winding numbers which are large enough to decay through the production of CP-violating CS numbers.
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