Electroweak baryogenesis

TL;DR

This review analyzes electroweak baryogenesis as a testable mechanism for the Universe's baryon asymmetry, detailing how a strongly first-order electroweak phase transition and CP-violating transport near bubble walls can generate the observed matter excess. It surveys perturbative and non-perturbative methods to study the phase transition, and discusses CP-violating source terms, diffusion dynamics, and washout constraints within SM extensions like the MSSM and scalar singlet models. The authors also map experimental probes across the intensity, high-energy, and cosmological frontiers, highlighting EDM limits, collider searches for light scalars, and gravitational-wave signatures as key tests. They emphasize remaining theoretical uncertainties, particularly in gauge-invariant BNPC calculations and CPV transport, and advocate further Monte Carlo studies and refined transport formalisms to solidify EWBG's viability. The work underlines the potential for terascale discoveries to either realize EWBG or place stringent constraints that favor alternative baryogenesis scenarios such as leptogenesis.

Abstract

Electroweak baryogenesis (EWBG) remains a theoretically attractive and experimentally testable scenario for explaining the cosmic baryon asymmetry. We review recent progress in computations of the baryon asymmetry within this framework and discuss their phenomenological consequences. We pay particular attention to methods for analyzing the electroweak phase transition and calculating CP-violating asymmetries, the development of Standard Model extensions that may provide the necessary ingredients for EWBG, and searches for corresponding signatures at the high energy, intensity, and cosmological frontiers.

Figures (13)

• Figure 1: Expanding bubbles of electroweak-broken phase within the surrounding plasma in the electroweak-symmetric phase.
• Figure 2: Baryon production in front of the bubble walls.
• Figure 3: Schematic temperature dependence of the effective potential.
• Figure 4: Dependence of the critical temperature $T_c$ in the MSSM on the SUSY-breaking RH stop mass parameter $m_U$ taken from Ref. Laine:1998qk (top panel) and Ref. Csikor:2000sq (bottom panel) . Note that the contribution to the ${\tilde{t}}_R$ mass-squared from this parameter goes as $-{\tilde{m}}_U^2=m_U^2$ . The phase labeled '' CB" or '' broken U" denotes a phase in which the stop field acquires a non-zero vacuum expectation value, corresponding to a color and charge-breaking vacuum. Top panel reprinted from M. Laine and K. Rummukainen, http://www.sciencedirect.com/science/article/pii/S0550321398005306 with permission from Elsevier. Bottom panel reprinted with permission from F. Csikor, Z. Fodor, P. Hegedus, A. Jakovac, S. D. Katz and A. Piroth, http://link.aps.org/doi/10.1103/PhysRevLett.85.932, copyright 2000 by the American Physical Society.
• Figure 5: Particle number profiles with respect to the bubble wall ($z=0$) obtained in the MSSM Chung:2009qs . Pink, green, and red curves give, respectively, number densities of third generation left-handed quarks, third generation left handed leptons, and total $n_L$. Bubble wall interior corresponds to $z>0$. Thin curves represent results of an analytic approximation valid sufficiently far in front of the wall. Reprinted from D. J. H. Chung, B. Garbrecht, M. .J. Ramsey-Musolf and S. Tulin, http://iopscience.iop.org/1126-6708/2009/12/067/ with permission from JHEP.