Quantum Transport and Electroweak Baryogenesis

TL;DR

The paper provides a principled derivation of quantum transport equations for electroweak baryogenesis using the Schwinger-Keldysh formalism, emphasizing the semiclassical force as a robust CP-violating source in many models. It links microscopic non-equilibrium dynamics to diffusion networks that produce the baryon asymmetry and analyzes how different scalar-sector extensions (singlets, two-Higgs-doublet models, MSSM, and beyond) achieve a strong first-order phase transition while satisfying EDM and collider constraints. The review highlights that viable EWBG typically requires extended scalar sectors with calculable CP-violating sources and carefully controlled washout, and it underscores how upcoming collider and EDM experiments will critically test these scenarios.

Abstract

We review the mechanism of electroweak baryogenesis. Our focus is on the derivation of quantum transport equations from first principles within the Schwinger-Keldysh formalism. We emphasize the importance of the semiclassical force approach, which provides reliable predictions in most models. In the light of recent electric dipole moment measurements and given the results on new physics searches from collider experiments, the status of electroweak baryogenesis is discussed in a variety of models.

Figures (12)

• Figure 1: Sketch of the electroweak baryogenesis mechanism: The Higgs bubble walls separate the symmetric from the broken phase. If the reflection of left-handed electroweak particles entails CP violation, the sphaleron process (that only is active in the symmetric phase) generates a net baryon number.
• Figure 2: The closed time path contour for a general out-of-equilibrium system (top) and a system in equilibrium at finite temperature (bottom).
• Figure 3: The plots show the required change in the top mass phase during the phase transition $\Delta \Theta_t$ in order to reproduce the observed baryon asymmetry. In the upper plot the wall thickness in terms of the temperature is kept constant, while in the bottom plot the wall thickness in terms of the critical vev is kept constant. The plots are adapted from ref. Espinosa:2011eu.
• Figure 4: The wall thickness $\ell_w$ as a function of the Higgs mass. The plot shows also the corresponding values of the scale of new physics $\Lambda$ and the ratio $\xi=\phi_c/T_c$. Plot adapted from Bodeker:2004ws.
• Figure 5: Two loop contribution to the electron EDM of Barr-Zee type.