Lower Bound on the Neutralino Mass from New Data on CMB and Implications for Relic Neutralinos

In the frame of an effective MSSM model without gaugino-mass unification at a grand unification (GUT) scale, we set a lower bound on the neutralino mass based on the new WMAP data on ${\mathrm{\Omega }}_{CDM}$. Our lower bound, $m_{\chi} \gsim 6$ GeV, leaves much room for relic neutralinos significantly lighter than those commonly considered ($m_{\chi }\text{gsim}50$ GeV). We prove that these light neutralinos may produce measurable effects in WIMP direct detection experiments of low energy threshold and large exposure.