Abstract
Electroweak baryogenesis is an attractive mechanism to generate the baryon asymmetry of the Universe via a strong first order electroweak phase transition. We compare the phase transition patterns suggested by the vacuum structure at the critical temperatures, at which local minima are degenerate, with those obtained from computing the probability for nucleation via tunneling through the barrier separating local minima. Heuristically, nucleation becomes difficult if the barrier between the local minima is too high, or if the distance (in field space) between the minima is too large. As an example of a model exhibiting such behavior, we study the Next-to-Minimal Supersymmetric Standard Model, whose scalar sector contains two SU(2) doublets and one gauge singlet. We find that the calculation of the nucleation probabilities prefers different regions of parameter space for a strong first order electroweak phase transition than the calculation based solely on the critical temperatures. Our results demonstrate that analyzing only the vacuum structure via the critical temperatures can provide a misleading picture of the phase transition patterns, and, in turn, of the parameter space suitable for electroweak baryogenesis.
Highlights
Smooth crossover in the Standard Model (SM) and, is not giving rise to sufficient deviations from thermal equilibrium [3]
We stress that for all slices of parameter space shown in figures 4–9, the region providing favorable conditions for electroweak baryogenesis via a Strong First Order Electroweak Phase Transition (SFOEWPT) differs markedly when the thermal history is inferred from the nucleation calculation instead of the simpler calculation of studying only the vacuum structure at the critical temperatures
Electroweak baryogenesis is a compelling scenario for the generation of the baryon asymmetry of the Universe
Summary
The Next-to-Minimal Supersymmetric Standard Model augments the particle content of the MSSM by a SM gauge-singlet chiral superfield S, see refs. [13, 14] for reviews. Of greater phenomenological interest is that the NMSSM can accommodate a 125 GeV SM-like Higgs boson without the need for large radiative corrections to its mass. The presence of the scalar gauge singlet makes a SFOEWPT achievable in the NMSSM [31,32,33,34,35,36,37,38,39,40,41,42,43,44,45, 47, 50] This should be contrasted with the situation in the MSSM, where, in the presence of a 125 GeV SM-like Higgs, the scalar potential is constrained such that a SFOEWPT is only possible if the stops are very light [5,6,7,8,9,10,11]. As we will see below, a relatively light singlet-like state gives the scalar potential a favorable shape for SFOEWPT The former option, the so-called alignment without decoupling limit, is more interesting for electroweak baryogenesis.
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