EVIDENCE OF HIGHER PRIMORDIAL LITHIUM FROM KECK OBSERVATIONS OF M92

Knowledge of the primordial lithium abundance (Li-p) tests and constra ins models of big bang nucleosynthesis and may have implications for d ark matter and the laws of physics. An apparent small dispersion in th e Li abundances of field halo dwarfs had been predicted to result from differences in the Li depletion of models with rotationally induced m ixing, and would imply a higher Li-p than is observed today in these s tars. However, this dispersion could also be explained by differential Galactic Li enrichment (from lower Li-p) coupled with a halo age spre ad and/or incomplete mixing. To differentiate between these possibilit ies, we have obtained Keck/HIRES observations at R = 45,000 in one of the oldest and most metal-poor globular clusters, M92, where different ial Li enrichment within the cluster is unlikely. We find some evidenc e for differences in the Li abundances of three otherwise apparently i dentical M92 subgiants in the Spite Li plateau. We provide evidence ag ainst cosmic-ray, supernova, and asymptotic giant branch star Li produ ction as causing these Li differences, and suggest that different stel lar surface Li depletion histories in these stars from a higher initia l abundance is a more likely explanation (as is also the case for open clusters). This higher initial abundance may have been the Li-p, or a combination of Li-p plus significant pre-M92 Galactic Li. Implication s are discussed.