COSMIC LITHIUM: GOING UP OR COMING DOWN ?

Observations of interstellar lithium provide a valuable complement to studies of lithium in Pop I and Pop II stars. Large corrections for unseen LiII and for non-gas phase lithium have provided obstacles to using interstellar data for abundance determinations. An approach to surmounting these difficulties is proposed and is applied to the Galaxy and the LMC. The key is that since potassium and lithium behave similarly regarding ionization and depletion, their observed ratio (LiI/KI) can be used to probe the abundance and evolution of lithium. For ten lines-of-sight in the interstellar medium of the Galaxy (ISM) the Li/K ratio observed $(\log (N_{Li}/N_K)_{ISM} = - 1.88 \pm 0.09)$ is entirely consistent with the solar system value $(\log (N_{Li}/N_{K})_{\odot} = - 1.82 \pm 0.05)$. The absence of LiI in front of SN87A in the LMC, coupled with the observed KI, corresponds to an upper bound (at \rsim 95 \% \ CL) of $\log (N_{Li}/N_K)_{LMC} < - 0.3 + \log (N_{Li}/N_K)_{ISM}.$ This low upper bound to LMC lithium suggests that cosmic lithium is on its way up from a primordial abundance lower, by at least a factor of two, than the present Pop I value of $[Li]_{PopI} \equiv 12 + \log (Li/H)_{PopI} = 3.2 \pm 0.1$.Comment: Submitted to the ApJ (Part 1), April 14, 199

BBN And The CBR Probe The Early Universe

Big Bang Nucleosynthesis (BBN) and the Cosmic Background Radiation (CBR) provide complementary probes of the early evolution of the Universe and of its particle content. Neutrinos play important roles in both cases, influencing the primordial abundances of the nuclides produced by BBN during the first 20 minutes, as well as the spectrum of temperature fluctuations imprinted on the CBR when the Universe is some 400 thousand years old. The physical effects relevant at these widely separated epochs are reviewed and the theoretical predictions are compared with observational data to explore the consistency of the standard models of cosmology and particle physics and to constrain beyond-the-standard-model physics and cosmology.Comment: 8 pages, 4 figures; to appear in Proceedings of SUSY06, the 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, 12-17 June 2006

Neutrinos And Big Bang Nucleosynthesis

According to the standard models of particle physics and cosmology, there should be a background of cosmic neutrinos in the present Universe, similar to the cosmic microwave photon background. The weakness of the weak interactions renders this neutrino background undetectable with current technology. The cosmic neutrino background can, however, be probed indirectly through its cosmological effects on big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) radiation. In this BBN review, focused on neutrinos and, more generally on dark radiation, the BBN constraints on the number of "equivalent neutrinos" (dark radiation), on the baryon asymmetry (baryon density), and on a possible lepton asymmetry (neutrino degeneracy) are reviewed and updated. The BBN constraints on dark radiation and on the baryon density following from considerations of the primordial abundances of deuterium and helium-4 are in excellent agreement with the complementary results from the CMB, providing a suggestive, but currently inconclusive, hint of the presence of dark radiation and, they constrain any lepton asymmetry. For all the cases considered here there is a "lithium problem": the BBN-predicted lithium abundance exceeds the observationally inferred primordial value by a factor of ~3.Comment: Invited Review article for the Special Issue on Neutrino Physics, Advances in High Energy Physics, 25 pages, 10 figure