Abstract
The mechanism of ``cold electroweak baryogenesis'' has been so far unpopular because its proposal has relied on the ad-hoc assumption of a period of hybrid inflation at the electroweak scale with the Higgs acting as the waterfall field. We argue here that cold baryogenesis can be naturally realized without the need to introduce any slow-roll potential. Our point is that composite Higgs models where electroweak symmetry breaking arises via a strongly first-order phase transition provide a well-motivated framework for cold baryogenesis. In this case, reheating proceeds by bubble collisions and we argue that this can induce changes in Chern-Simons number, which in the presence of new sources of CP violation commonly lead to baryogenesis. We illustrate this mechanism using as a source of CP violation an effective dimension-six operator which is free from EDM constraints, another advantage of cold baryogenesis compared to the standard theory of electroweak baryogenesis. Our results are general as they do not rely on any particular UV completion but only on a stage of supercooling ended by a first-order phase transition in the evolution of the universe, which can be natural if there is nearly conformal dynamics at the TeV scale. Besides, baryon-number violation originates from the Standard Model only.
Highlights
The mechanism of “cold electroweak baryogenesis” has been so far unpopular because its proposal has relied on the ad-hoc assumption of a period of hybrid inflation at the electroweak scale with the Higgs acting as the waterfall field
First-order phase transitions have been commonly studied based on standard polynomial potentials, in which case the amount of supercooling is not sufficient for cold baryogenesis to work
Nearly conformal potentials coupled to the Higgs sector, as motivated by a dynamical solution to EW symmetry breaking, can lead to the ideal conditions for a cold electroweak phase transition [33]
Summary
The main idea of cold baryogenesis relies on the evolution of winding number and ChernSimons number in a fast tachyonic EW transition. Since the system has to approach the vacuum at later stages, the Higgs winding has to either decay (L → ∞) or be dressed by the gauge fields (Ai → ∂iΩΩ−1) In the latter case, this leads to a change in Chern Simons number, a change in baryon number. This problem was cured in the so-called non-local (by charge transport) and standard EW baryogenesis mechanism [50] where CP violation originates in the fermionic sector and is transported by diffusion into the symmetric phase where sphaleron transitions are unsuppressed and biased by the CP-violating fermion densities, producing the baryon asymmetry In this case, the asymmetry is produced at high temperature and leads to strong constraints on the finite temperature Higgs potential nature via the sphaleron bound φ/T 1 where φ and T are evaluated at the nucleation temperature.
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