Discussing direct search of dark matter particles in the Minimal Supersymmetric extension of the Standard Model with light neutralinos

TL;DR

This work revisits light neutralinos within an effective MSSM (effMSSM) at the electroweak scale, motivated by DAMA/LIBRA and other DM hints, and assesses whether Tevatron and B-factory data impose strong constraints. Through analytic relic-density reasoning and a focused numerical scan of the LNM_A parameter space, it shows a robust lower limit $m_\ uchi \gtrsim 7$–$8$ GeV and a neutralino-nucleon cross-section in the range needed to explain direct-detection signals, while remaining largely compatible with collider and flavor bounds. The analysis highlights substantial hadronic uncertainties (notably in $g_d$) and argues that, unlike some SUGRA scenarios, current collider bounds have only mild impact on the light neutralino population; it also discusses implications for indirect searches and future LHC tests. Overall, the paper demonstrates that a light neutralino population within the LNM remains a viable DM candidate capable of reconciling several direct-detection hints under reasonable astrophysical and hadronic assumptions.

Abstract

We examine the status of light neutralinos in an effective Minimal Supersymmetric extension of the Standard Model (MSSM) at the electroweak scale which was considered in the past and discussed in terms of the available data of direct searches for dark matter (DM) particles. Our reanalysis is prompted by new measurements at the Tevatron and B-factories which might potentially provide significant constraints on the MSSM model. Here we examine in detail all these new data and show that the present published results from the Tevatron and B-factories have only a mild effect on the original light neutralino population. This population, which fits quite well the DAMA/LIBRA annual modulation data, would also agree with the preliminary results of CDMS, CoGeNT and CRESST, should these data, which are at present only hints or excesses of events over the expected backgrounds, be interpreted as authentic signals of DM. For the neutralino mass we find a lower bound of 7-8 GeV. Our results differ from some recent conclusions by other authors because of a few crucial points which we try to single out and elucidate.

Figures (25)

• Figure 1: Scatter plot of the light neutralino population for the LNM--$\cal A$ scan, shown in the plane $m_{\chi}-\tan \beta$. The (red) solid line represents the analytic bound from the neutralino relic abundance given in Eq. (\ref{['ma']}).
• Figure 2: Scatter plot for $\Gamma(Z \rightarrow \chi \chi)$ versus $m_{\chi}$ for the LNM--$\cal A$ scan. The (red) solid horizontal line denotes the present experimental upper bound to the invisible width of the Z--decay into non Standard Model particles.
• Figure 3: Scatter plot of the absolute value of the Wilson coefficients $|C_S^i|$ for each SUSY contribution to the $BR(B_s \rightarrow \mu^+ \mu^-)$ (colored points), compared to the full calculation of the dominant term (black points) (for expressions of these quantities see Refs. bobetharnowittburaseos), for the LNM--$\cal A$ scan. The sign of each term is indicated in parenthesis as "$[+]$" and "$[-]$". The values of $|C_S^i|$ are plotted as functions of the neutralino mass $m_\chi$.
• Figure 4: The same as in Fig. \ref{['fig:scat_mchi_bsmumu_contrib0']}, except that the Wilson coefficients $|C_S^i|$ are plotted as functions of $\tan\beta$.
• Figure 5: Scatter plot of the ratio between the full numerical calculation of $BR(B_s \rightarrow \mu^+ \mu^-)$ and the approximate expression of the dominant term $BR^{(6)}(B_s \rightarrow \mu^+ \mu^-)$ given in Eq. (\ref{['mumu4']}), for the LNM--$\cal A$ scan. The scatter plot is shown as a function of the neutralino mass $m_\chi$.