The baryogenesis window in the MSSM

TL;DR

The paper investigates the strength of the electroweak phase transition in the MSSM with light stops to assess the viability of electroweak baryogenesis. It employs a perturbative finite-temperature effective potential, including Daisy resummation and two-loop QCD corrections, across arbitrary $m_A$ to map the transition strength. The authors find that two-loop corrections significantly strengthen the transition, extending the viable baryogenesis window to regions with $2<\tan\beta<4$ and $m_A>\sim120$ GeV, with a light Higgs $m_h\lesssim85$ GeV and stops not necessarily lighter than the top. They also discuss the sensitivity to Higgs-sector mass scales, potential crossover at high Higgs masses, and agreement with 3d lattice studies, highlighting testability by LEP II.

Abstract

Thermal two-loop QCD corrections associated with light stops have a dramatic effect on the strength of the MSSM electroweak phase transition, making it more strongly first order as required for the viability of electroweak baryogenesis. We perform a perturbative analysis of the transition strength in this model, including these important contributions, extending previous work to arbitrary values of the pseudoscalar Higgs boson mass, m_A. We find a strong enough transition in a region with 2< tan beta < 4 and m_A > 120 GeV, a light Higgs boson with nearly standard couplings, and mass below 85 GeV within the reach of LEP II, and one stop not much heavier than the top quark. In addition, we give a qualitative discussion of the parameter space dependence of the transition strength and comment on the possibility that the transition turns to a crossover for sufficiently large Higgs masses.

Figures (5)

• Figure 1: Critical Higgs boson mass for crossover in the MSSM [as estimated by formula (\ref{['mhcmssm']})]. The parameter $r$ measures the effect of stops on the transition: $r=0$ corresponds to the pure SM limit and realistic values of $r$ should not be larger than $0.2-0.3$.
• Figure 2: Order parameter $v/T$ at $T_c$ as a function of the pseudoscalar mass $m_A$. Curve $(a)$ corresponds to the 2-loop resummed approximation, while $(b)$ gives the 1-loop resummed result. Here $M_t=156\ GeV$, $m_Q=70\ GeV$, $m_U=0$ and $\tan\beta=2.5$.
• Figure 3: Two-loop vacuum graphs contributing to the effective potential (in Landau gauge). Dashed lines represent Higgs bosons, wiggled lines gauge bosons, dotted lines ghosts. Dashed lines with an arrow represent squarks, while quarks are solid lines with an arrow.
• Figure 4: Lines of $v/T_c$ (solid) for different values of $\tan\beta$ as a function of $m_A$. The mass of the lightest $CP$--even Higgs is given by the dashed contour lines. $M_t=156\ GeV$, $m_U=0$, $m_Q=70\ GeV$.
• Figure 5: Same as fig. 4 but for $M_t=175\ GeV$, $m_U=0$, $m_Q=250\ GeV$.