MSSM Baryogenesis and Electric Dipole Moments: An Update on the Phenomenology

TL;DR

This paper updates the phenomenology of MSSM electroweak baryogenesis by integrating two-loop EDM calculations, allowing non-universal CP-violating phases, and incorporating cosmological entropy-dilution effects that can rescale the neutralino relic density and the BAU. It maps viable regions in gaugino–Higgsino parameter space and in the $( aneta,m_A)$ plane under heavy sfermions, identifying robust lower bounds on the electron and neutron EDMs that are near or exceed next-generation experimental sensitivities, thereby making MSSM EWB highly testable. The work highlights that relic-density dilution can substantially tighten the viable MSSM EWB parameter space, especially for wino–Higgsino–driven baryogenesis, while bino–Higgsino scenarios remain comparatively less affected but still constrained. Overall, MSSM EWB presents concrete, testable predictions for upcoming EDM experiments, with theoretical uncertainties in transport dynamics identified as key directions for future refinement.

Abstract

We explore the implications of electroweak baryogenesis for future searches for permanent electric dipole moments in the context of the minimal supersymmetric extension of the Standard Model (MSSM). From a cosmological standpoint, we point out that regions of parameter space that over-produce relic lightest supersymmetric particles can be salvaged only by assuming a dilution of the particle relic density that makes it compatible with the dark matter density: this dilution must occur after dark matter freeze-out, which ordinarily takes place after electroweak baryogenesis, implying the same degree of dilution for the generated baryon number density as well. We expand on previous studies on the viable MSSM regions for baryogenesis, exploring for the first time an orthogonal slice of the relevant parameter space, namely the (tanβ, m_A) plane, and the case of non-universal relative gaugino-higgsino CP violating phases. The main result of our study is that in all cases lower limits on the size of the electric dipole moments exist, and are typically on the same order, or above, the expected sensitivity of the next generation of experimental searches, implying that MSSM electroweak baryogenesis will be soon conclusively tested.

Figures (10)

• Figure 1: Iso-level curves for the lightest neutralino relic abundance (upper panels) and for the gaugino-higgsino CPV phase producing the central value of the BAU, without (central panels) and with (lower panels) entropy rescaling for models with over-abundant relic neutralinos. All panels refer to the ($M_1,\mu$) plane, with $m_A=150$ GeV in the left panels, and $m_A=500$ GeV for those to the right. The red shaded region is excluded by the non-observation of light neutralino pairs at LEP. The green bands correspond to a neutralino relic density consistent with the WMAP results. The blue dashed lines in the upper panels indicate a lightest neutralino mass of 125 GeV.
• Figure 2: Curves at constant CPV gaugino-higgsino phase, on the ($M_1,\mu$) plane, at $m_A=300$ GeV and $M_2=2M_1$, with (right) and without (left) entropy rescaling for overabundance relic neutralinos models. The grey region does not produce a large enough BAU through resonant processes, the red region is excluded by LEP searches for the lightest chargino, and the green lines indicate a neutralino relic abundance equal to the cold dark matter abundance in a standard cosmological setup.
• Figure 3: Curves of constant values for the electron (left) and for the neutron (right) electric dipole moment, on the same plane as Fig. \ref{['fig:phimu300']}, right. The regions outside the blue contours are excluded by current experimental limits.
• Figure 4: Curves indicating the values of a common sfermion mass scale such that one and two loop contributions to the electron (left) and to the neutron (right) EDM are equal, on the same plane as Fig. \ref{['fig:phimu300']}, right. At a given sfermion mass scale indicated on the lines, points inside the funnel region lying closer to the origin correspond to two-loop contributions that are larger in magnitude than one-loop contributions. The converse holds for points lying closer to the funnel tips.
• Figure 5: Curves indicating constant values of the relative bino-higgsino phase $\phi_1$ that produces the right BAU through resonant processes, on the same plane as fig. \ref{['fig:phimu300']} (left), and on the plane defined by $M_1$ and by the relative bino-higgsino mass splitting $(\mu-M_1)/M_1$. The grey region does not produce a large enough BAU through resonant processes, the red region is excluded by LEP searches for the lightest chargino. In the left panel, the green lines indicate a neutralino relic abundance equal to the cold dark matter abundance in a standard cosmological setup. In the right panel, the blue dashed line indicates a lightest neutralino mass of 125 GeV.