Electroweak Baryogenesis And The Fermi Gamma-Ray Line

TL;DR

This work investigates whether NMSSM regions capable of explaining the tentative $130$ GeV Fermi gamma-ray line via resonant bino-like neutralino annihilation can simultaneously support electroweak baryogenesis. By exploiting the NMSSM’s singlet sector, the authors show that a strongly first-order electroweak phase transition can occur without a light stop, while CP-violating higgsino-wino interactions can generate the observed baryon asymmetry, all within constraints from DM relic density, direct/indirect detection, Higgs data, and EDMs. A concrete EWPT benchmark demonstrates a barrier driven by tree-level singlet couplings and yields $T_c\approx 72$ GeV with $\varphi(T_c)/T_c\approx 1.14$, compatible with a $125$ GeV SM-like Higgs and the $130$ GeV line. The scenario makes concrete, testable predictions: upcoming EDM measurements, DM searches, gamma-ray data, and Higgs coupling studies at the LHC can validate or falsify this unified explanation for both baryonic and dark matter in the Universe.

Abstract

Many particle physics models attempt to explain the 130 GeV gamma-ray feature that the Fermi-LAT observes in the Galactic Center. Neutralino dark matter in non-minimal supersymmetric models, such as the NMSSM, is an especially well-motivated theoretical setup which can explain the line. We explore the possibility that regions of the NMSSM consistent with the 130 GeV line can also produce the observed baryon asymmetry of the universe via electroweak baryogenesis. We find that such regions can in fact accommodate a strongly first-order electroweak phase transition (due to the singlet contribution to the effective potential), while also avoiding a light stop and producing a Standard Model-like Higgs in the observed mass range. Simultaneously, CP-violation from a complex phase in the wino-higgsino sector can account for the observed baryon asymmetry through resonant sources at the electroweak phase transition, while satisfying current constraints from dark matter, collider, and electric dipole moment (EDM) experiments. This result is possible by virtue of a relatively light pseudoscalar Higgs sector with a small degree of mixing, which yields efficient s-channel resonant neutralino annihilation consistent with indirect detection constraints, and of the moderate values of $μ$ required to obtain a bino-like LSP consistent with the line. The wino mass is essentially a free parameter which one can tune to satisfy electroweak baryogenesis. Thus, the NMSSM framework can potentially explain the origins of both baryonic and dark matter components in the Universe. The tightness of the constraints we impose on this scenario makes it extraordinarily predictive, and conclusively testable in the near future by modest improvements in EDM and dark matter search experiments.

Figures (5)

• Figure 1: The dominant diagram leading to the two-photon pair-annihilation of neutralinos in the NMSSM scenario under consideration in this study.
• Figure 2: The zero-temperature thermally-averaged cross-section times velocity for neutralino annihilation into two photons as a function of the singlet-like pseudoscalar mass $m_{A_1}$ for the EWPT benchmark point discussed in Sec. \ref{['sec:EWPT']}: $\lambda=0.75$, $\kappa=0.45$, $\tan\beta=1.7$, $A_{\lambda}=545$ GeV, $A_{\kappa}=-88$ GeV, $\mu=275.8$ GeV, $M_1=143.5$ GeV, and $M_2=635.5$ GeV. The red dashed line indicates the lower bound on $\left<\sigma v\right>_{\gamma \gamma}$ required to produce the 130 GeV Fermi line. Note that decreasing $M_1$ (thereby increasing $\mu$) will narrow down the resonance.
• Figure 3: An example of the NMSSM parameter space for successful electroweak baryogenesis and a 130 GeV gamma-ray line. Here we take $\lambda=0.6$, $\kappa=0.32$, $\tan\beta=1.8$ and $\Delta=0$ (so that the CP-violating sources are on resonance), while the rest of the parameters are chosen as described in Sec. \ref{['subsec:suitable']} to be consistent with the Fermi line. The gray shaded region is excluded by the XENON100 225 live day results, calculated with the default settings in MicrOmegas. Red shaded regions are excluded by measurements of the Higgs mass (although these regions can be shifted around by changing e.g. the squark masses). The orange shaded region is excluded by the non-observation of an electric dipole moment of the electron. The blue contours correspond to points consistent with the observed baryon-to-entropy ratio of the universe for different values of the CP-violating phase $\phi$.
• Figure 4: The phase structure for the benchmark point with first-order phase transitions. The dotted line gives the temperature-dependent singlet field values, and the solid line gives the temperature-dependent Higgs doublet field values.
• Figure 5: A contour plot of the effective potential just below the critical temperature. The electroweak broken minimum is represented by the dot on the upper-right, while the symmetric minimum is on the lower left. The actual tunneling happens along the curved solid black line.