Neutralinos, big bang nucleosynthesis, and {sup 6}Liin low-metallicity stars

The synthesis of {sup 6}Li during the epoch of big bang nucleosynthesis due to residual annihilation of dark matter particles is considered. By comparing the predicted {sup 6}Li to observations of this isotope in low-metallicity stars, generic constraints on s-wave dark matter annihilation rates into quarks, gauge bosons, and Higgs bosons are derived. It may be shown that, for example, wino dark matter in anomaly-mediated SUSY breaking scenarios with masses m{sub {chi}} < or approx. 250 GeV or light neutralinos with m{sub {chi}} < or approx, 20 GeV annihilating into light quarks are, taking face value, ruled out. These constraints may only be circumvented if significant {sup 6}Li depletion has occurred in all three low-metallicity stars in which this isotope has been observed to date. In general, scenarios invoking nonthermally generated neutralinos with enhanced annihilation rates for a putative explanation of cosmic ray positron or galactic center as well as diffuse background gamma-ray signals by present-day neutralino annihilation will have to face a stringent {sup 6}Li overproduction problem. On the other hand, it is possible that {sup 6}Li as observed in low-metallicity stars is entirely due to residual dark matter annihilation during big bang nucleosynthesis, even for neutralinos undergoing amore » standard thermal freeze-out.« less