Revival of the Thermal Sneutrino Dark Matter

Abstract

The left-handed sneutrino in the Minimal Supersymmetric Standard Model (MSSM) has been ruled out as a viable thermal dark matter candidate, due to conflicting constraints from direct detection experiments and from the measurement of the dark matter relic density. The intrinsic fine-tuning problem of the MSSM, however, motivates an extension with a new U(1)' gauge symmetry. We show that in the U(1)'-extended MSSM the right-handed sneutrino becomes a good thermal dark matter candidate. We identify two generic parameter space regions where the combined constraints from relic density determinations, direct detection and collider searches are all satisfied.

Figures (3)

• Figure 1: Relic density $\Omega_{\widetilde{\nu}_R} h^2$ of the RH sneutrino versus its mass $M_{\widetilde{\nu}_R}$, for $\theta_{E6} = \pi/3$, $g_{Z'}=g_1$, and fixed $\widetilde{Z}'$ mass as $M_{\widetilde{Z}'} = 1.5 M_{\widetilde{\nu}_R}$. Results are shown for three different values of $M_{Z'}$: 500 GeV (red), 1000 GeV (blue), and 2000 GeV (magenta). The shaded region is the $2 \sigma$ range of $\Omega_{\rm CDM} h^2$ allowed by WMAP+SDSS WMAP3. The dotted line traces the minimum value of $\Omega_{\widetilde{\nu}_R}h^2$ on the $Z'$ resonance.
• Figure 2: Spin-independent cross-section (normalized to a single nucleon) of the sneutrino-nucleus interaction versus $M_{\widetilde{\nu}_R}$ for a Germanium type detector, for the same parameter choices as in Fig. \ref{['fig:relic']}. The dotted (solid) portions of the curves correspond to unacceptable (acceptable) values for $\Omega_{\widetilde{\nu}_R} h^2$, while in the yellow shaded region $\widetilde{\nu}_R$ can singlehandedly explain all of the dark matter in the Universe. The green curves are the current (solid) and projected (dashed) limits from the CDMS experiment CDMS2.
• Figure 3: Experimental constraints on the ($\theta_{E6},M_{Z'}$) parameter space in the resonance funnel region $M_{\widetilde{\nu}_R}\sim M_{Z'}/2$, for fixed $g_{Z'}=g_1$ and $M_{\widetilde{Z}'} = 1.5 M_{\widetilde{\nu}_R}$. The upper (light blue) shaded region is cosmologically excluded, while the lower (green) shaded region is currently ruled out by CDMS. The squares indicate the most recent $Z'$ mass bounds from CDF Z2masslimit. The dotted curves BBN are the lower bounds on $M_{Z'}$ from the discrepancy in the $^4$He abundance, for an effective neutrino number of $\Delta N = 0.3$ (upper, red curve) and $\Delta N = 1$ (lower, blue curve), and for $T_c = 150~ {\rm MeV}$. The singular point $\theta_{E6} = 0.42 \pi$ corresponds to $Q'(\nu_R) = 0$.