Neutralinos, big bang nucleosynthesis, andL6iin low-metallicity stars

The synthesis of ${}^6\mathrm{L}\mathrm{i}$ during the epoch of big bang nucleosynthesis due to residual annihilation of dark matter particles is considered. By comparing the predicted ${}^6\mathrm{L}\mathrm{i}$ 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 $m_{\chi }\lesssim 250\mathrm{G}\mathrm{e}\mathrm{V}$ or light neutralinos with $m_{\chi }\lesssim 20\mathrm{G}\mathrm{e}\mathrm{V}$ annihilating into light quarks are, taking face value, ruled out. These constraints may only be circumvented if significant ${}^6\mathrm{L}\mathrm{i}$ 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 ${}^6\mathrm{L}\mathrm{i}$ overproduction problem. On the other hand, it is possible that ${}^6\mathrm{L}\mathrm{i}$ as observed in low-metallicity stars is entirely due to residual dark matter annihilation during big bang nucleosynthesis, even for neutralinos undergoing a standard thermal freeze-out.