Light Neutralinos with Large Scattering Cross Sections in the Minimal Supersymmetric Standard Model

Abstract

Motivated by recent data from CoGeNT and the DAMA annual modulation signal, we discuss collider constraints on MSSM neutralino dark matter with mass in the 5-15 GeV range. Such an LSP would be a Bino with a small Higgsino admixture. Maximization of the DM-nucleon scattering cross section for such a WIMP requires a light Higgs boson with tan beta enhanced couplings. Limits on the invisible width of the Z boson, when combined with Tevatron constraints on Higgs bosons at large tan beta, and the rare decay $B^{\pm} \to τν$ constrain cross sections to be below $σ_n \lesssim 2 \times 10^{-41} {cm}^2$. This indicates a slight local Dark Matter over-density would be necessary to explain the CoGeNT excess. This scenario also requires a light charged Higgs boson, which can give substantial contributions to rare decays such as $b \to s γ$ and $t \to b H^+$.

Figures (3)

• Figure 1: Constraints from $t \rightarrow b H^+$ in the $m_{H^\pm}-\tan\beta$ plane. The black solid lines indicate lines of constant scattering cross section, assuming the limit on the Higgsino fraction from the invisible $Z$ width is saturated. The dashed blue lines show the limits from $t \rightarrow b H^+$ for various branching ratios (labeled accordingly on the blue dashed lines), assuming $\epsilon_Y = 0$ and $\epsilon_0 = + 6 \times 10^{-3}$. The dotted red lines show the $\epsilon_0 = - 6 \times 10^{-3}$ limits.
• Figure 2: Constraints on the $m_A-\tan\beta$ plane from $B \rightarrow \tau \nu$, $B \rightarrow D \tau \nu$ and $\phi \rightarrow \tau^+ \tau^-$. In the case of the $B$ decays, we show a conservative bound (grey shaded region): the intersection of the 3 sigma allowed regions for both $B$ processes. For $\phi \rightarrow \tau^+ \tau^-$ (the irregular red shaded region), the region below the curve is allowed at 2 $\sigma$ by the Tevatron. The B-decay region depends on the squark and gluino masses due to loop corrections to the $b$ mass, so we show the region corresponding to $\epsilon_0=+\epsilon_{max}$. The region for $\epsilon_0=-\epsilon_{max}$ is shown in Fig. \ref{['fig:summary2']}. The $\phi \rightarrow \tau^+ \tau^-$ is relatively insensitive to these corrections. We also show in this plane contours of constant scattering cross section, assuming the bound on the invisible $Z$ width (3.0 MeV) is saturated and $\epsilon_0 = + \epsilon_{max}$.
• Figure 3: Constraints on the $m_A-\tan\beta$ plane from $B \rightarrow \tau \nu$, $B \rightarrow D \tau \nu$ and $\phi \rightarrow \tau^+ \tau^-$, and $t \rightarrow b H^+$. In the case of the B decays, we show a conservative bound (grey shaded region): the intersection of the 3 sigma allowed regions for both $B$ processes. For $\phi \rightarrow \tau^+ \tau^-$ (the irregular red shaded region), the region below the curve is allowed at 2 $\sigma$ by the Tevatron. Since the B-decay region depends on the squark and gluino masses due to loop corrections to the $b$ mass, we show lines corresponding to $\epsilon_0=-\epsilon_{max}$. The region for $\epsilon_0=+\epsilon_{max}$ is shown in Fig. \ref{['fig:summary1']}. The $\phi \rightarrow \tau^+ \tau^-$ constraint is relatively insensitive to these corrections. The green shaded region indicates the constraint from $t \rightarrow b H^+$. We also show in this plane contours of constant scattering cross section, assuming the bound on the invisible $Z$ width (3.0 MeV) is saturated and $\epsilon_0 = - \epsilon_{max}$.