Lower bound on the neutralino mass from new data on CMB and implications for relic neutralinos

Abstract

In the framework of an effective minimal supersymmetric extension of the standard model without gaugino-mass unification at a grand unification scale, we set a lower bound on the neutralino mass based on the new WMAP data on ${\ensuremath{\Omega}}_{\mathrm{CDM}}$ $(R$-parity conservation is assumed). Our lower bound ${m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}6\mathrm{GeV}$ leaves much room for relic neutralinos significantly lighter than those commonly considered ${(m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}50\mathrm{GeV}).$ We prove that these light neutralinos may produce measurable effects in weakly interacting massive particle direct detection experiments of low energy threshold and large exposure.