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 ΩCDM. Our lower bound, $m_{\chi} \gsim 6$ GeV, leaves much room for relic neutralinos significantly lighter than those commonly considered ($m_{\chi} \gsim 50$ GeV). We prove that these light neutralinos may produce measurable effects in WIMP direct detection experiments of low energy threshold and large exposure.