Cold Dark Matter Candidate in a Class of Supersymmetric Models with an Extra U(1)

TL;DR

In SUSY frameworks with an extra $U(1)'$ broken at the TeV scale by a SM-singlet $S$, a very light, singlino-dominated neutralino can be a viable cold dark matter candidate. The authors analyze the LSP composition, derive its thermal relic density via $Z'$-mediated annihilation, and estimate halo direct-detection rates; they find $ ext{Ωχ} h^2$ can fall in the cosmologically interesting window for plausible $M_{Z'}$ values and couplings. Direct detection signals are predicted to be small but potentially accessible to next-generation experiments, with scalar couplings to nuclei often dominating for heavy targets. This work demonstrates a viable dark matter candidate beyond the MSSM and links dark matter phenomenology to TeV-scale $Z'$ physics and the dynamics of the Higgs singlet.

Abstract

In supersymmetric models whose gauge group includes an additional U(1) factor at the TeV scale, broken by the VEV of an standard model singlet S, the parameter space can accommodate a very light neutralino not ruled out experimentally. This higgsino-like fermion, stable if R-parity is conserved, can make a good cold dark matter candidate. We examine the thermal relic density of this particle and discuss the prospects for its direct detection if it forms part of our galactic halo.

Figures (3)

• Figure 1: Contour plot of the lightest neutralino mass ($m_\chi/GeV$) in the plane $M_1'-M_{Z'}$ with $Q_1=Q_2=1$ and $\tan\beta=1$. In the region delimited by the thick solid lines, the light neutralino has the composition (\ref{['N']}) with a purity $\geq 0.99$.
• Figure 2: Relic abundance of $\chi$ as a function of its mass (in GeV) for $Q_1=Q_2=1$ and different values of $M_{Z'}$ from 300 GeV (lower curve) to 800 GeV (upper).
• Figure 3: Detection rates for $^{73}$Ge and $^{29}$Si detectors.