Enhanced cosmological Li6 abundance as a potential signature of residual dark matter annihilations

Residual late-time dark matter particle annihilations during and after big-bang nucleosynthesis may alter the predicted cosmological abundances of the light elements. Within the constrained minimal supersymmetric extension of the standard model with a neutralino as the lightest supersymmetric particle, we find negligible effects on the abundances of deuterium, He3, He4, and Li7 predicted by homogeneous big-bang nucleosynthesis, but potentially a large enhancement in the predicted abundance of Li6. This enhancement may be as much as 2 orders of magnitude in the focus-point WMAP strip and in the coannihilation and funnel regions for large tan β for small m _1/2, and the effect is still significant at large m _1/2. However, the potential Li6 enhancement is negligible in the part of the coannihilation strip for tan β=10 that survives the latest LHC constraints. A similar enhancement of the Li6 abundance may also be found in a model with common, nonuniversal Higgs masses (the NUHM1).