Extended MSSM Neutralinos as the Source of the PAMELA Positron Excess

Abstract

We consider a scenario within the Minimal Supersymmetric Standard Model extended by a singlet chiral superfield, in which neutralino dark matter annihilates to light singlet-like Higgs bosons, which proceed to decay to either electron-positron or muon-antimuon pairs. Unlike neutralino annihilations in the MSSM, this model can provide a good fit to the PAMELA cosmic ray positron fraction excess. Furthermore, the singlet-like scalar Higgs can induce a large Sommerfeld enhancement and provide an annihilation rate sufficient to accommodate the observed positron excess.

Figures (1)

• Figure 1: The cosmic ray positron fraction resulting from neutralino annihilations in several selected scenarios. In each case, we consider the channel $\chi^0 \chi^0 \rightarrow ah$, followed by $h \rightarrow aa$, and $a\rightarrow e^+ e^-$ (top) or $\mu^+ \mu^-$ (bottom). In the upper (lower) frame, we have used $m_h=3$ GeV (10 GeV), although the precise value of this mass has only a small effect of the shape of the electron/positron spectrum. In each case, we have normalized the annihilation rate to accommodate the PAMELA data. The dot-dashed line denotes the prediction from astrophysical secondary production alone.