Bino-driven Electroweak Baryogenesis with highly suppressed Electric Dipole Moments

TL;DR

The paper tackles the tension between electroweak baryogenesis (EWB) and electric dipole moment (EDM) bounds within the MSSM by focusing on CP violation in the bino sector. It shows that the CP-violating phase $\phi_1=\mathrm{Arg}(\mu M_1 b^*)$ can drive successful EWB with EDMs largely suppressed compared to the wino-driven case, due to reduced two-loop contributions and gauge-coupling suppressions; achieving a strongly first-order EWPT requires a light right-handed stop, with resonant enhancement when $|\mu|\approx|M_1|$. The bino-driven scenario thus emerges as the most EDM-compatible MSSM EWB framework, though it remains testable through collider phenomenology and dark matter searches, and will be probed further by future EDM experiments. Together, these results broaden the viable parameter space for MSSM EWB and lessen the tension with EDM constraints, highlighting a concrete path to observable baryogenesis without large EDM signatures.

Abstract

It is conventional wisdom that successful electroweak baryogenesis in the Minimal Supersymmetric extension of the Standard Model (MSSM) is in tension with the non-observation of electric dipole moments (EDMs), since the level of CP-violation responsible for electroweak baryogenesis is believed to generate unavoidably large EDMs. We show that CP-violation in the bino-Higgsino sector of the MSSM can account for successful electroweak baryogenesis without inducing large EDMs. This observation weakens the correlation between electroweak baryogenesis and EDMs, and makes the bino-driven electroweak baryogenesis scenario the least constrained by EDM limits. Taking this observation together with the requirement of a strongly first-order electroweak phase transition, we argue that a bino-driven scenario with a light stop is the most phenomenologically viable MSSM electroweak baryogenesis scenario.

Figures (4)

• Figure 1: The complete list of all chargino-neutralino two-loop diagrams contributing to EDMs of leptons and quarks. The external photon line is attached to the charged particles in each diagram in all possible ways. Mirror graphs are not displayed.
• Figure 2: The electron (left) and neutron (right) electric dipole moment as a function of the bino and wino phase.
• Figure 3: The green band shows the region, in the ($M_1,{\rm sin}\phi_1$) plane compatible with electroweak baryogenesis. We assume that ${\rm sin}\phi_2=0$. On the same plane, we indicate iso-level curves at constant values for the electron (left) and for the neutron (right) EDMs.
• Figure 4: The green band shows the region, in the ($M_2,{\rm sin}\phi_2$) plane compatible with electroweak baryogenesis. We assume that ${\rm sin}\phi_1=0$. On the same plane, we indicate iso-level curves at constant values for the electron (left) and for the neutron (right) EDMs. Parameter space points above the red lines are excluded by current experimental constraints on electron and neutron EDMs.