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Deuterium plays a crucial role in testing big-bang nucleosynthesis. Its chemical evolution, while simple (it is burned to $^3$He), is intertwined with the more complicated evolution of $^3$He. Gloeckler \& Geiss' new measurement of the $^3$He abundance and the HST measurement of D, both in the local ISM today, can be compared to the pre-solar nebula abundances of D and $^3$He. Within the uncertainties, the sum of D + $^3$He relative to hydrogen is unchanged. This provides some validation of the cosmological utility of D + $^3$He, first suggested by Yang et al (1984), and further, indicates that over the past 4.5 Gyr there has been at most modest stellar production of $^3$He, in contradiction with stellar modeling, or modest stellar destruction of $^3$He, in contradiction with some ``solar spoons.'' While the earlier Galactic evolution of D + $^3$He cannot be constrained directly, it is expected to be dominated by massive stars, which deplete their $^3$He and produce metals. Based on the Galactic metallicity and the constancy of D + $^3$He over the past 4.5 Gyr, we derive a more empirically based lower bound to the cosmological baryon density; while not dramatically different from the original bound of Yang et al (1984) based on D + $^3$He, it alleviates some of the cosmic tension between the big-bang $^4$He abundance and those of D and $^3$He., 15 pages + 2 figures (included as eps files using epsf.sty and rotate.sty), submitted to Nature

Deuterium is the best indicator of the baryon density; however, only its present abundance is known (and only locally) and its chemical evolution is intertwined with that of $^3$He. Because galactic abundances are spatially heterogeneous, mean chemical-evolution models are not well suited for extrapolating the pre-solar D and $^3$He abundances to their primeval values. We introduce a new approach which explicitly addresses heterogeneity, and show that the decade-old big-bang nucleosynthesis concordance interval $\eta \approx (2 -8)\times 10^{-10}$ based on D and $^3$He is robust., Comment: 9 pages, LaTeX(2.09), 4 postscript figures (attached). A postscript version with figures can be found at ftp://astro.uchicago.edu/pub/astro/chem_evolution. (See the README file for details). REVISION: Numerous changes have been made to the text and the focus of the discussion has changed

If the hot, X-ray emitting gas in rich clusters forms a fair sample of the universe (as in Cold Dark Matter (CDM) models), and the universe is at the critical density, $\Omega_T = 1$, then the data appears to imply a baryon fraction, $\Omega_{b,x}$ ($\Omega_{b,x}\equiv \Omega_b$ derived from X-ray cluster data), larger than that predicted by Big Bang Nucleosynthesis (BBN). While various other systematic effects such as clumping can lower $\Omega_{b,x}$, in this paper we use an elementary analysis to show that a simple admixture of Hot Dark Matter (HDM, low mass neutrinos) with CDM to yield mixed dark matter shifts $\Omega_{b,x}$ down so that significant overlap with $\Omega_b$ from BBN can occur for $H_0 \lsim 75\;{\rm km/sec/Mpc}$, even without invoking the possible aforementioned effects. The overlap interval is slightly larger for lower mass neutrinos since fewer cluster on the scale of the hot X-ray gas. We illustrate this result quantitatively in terms of a simple isothermal model. More realistic velocity dispersion profiles, with less centrally-peaked density profiles, imply that fewer neutrinos are trapped and, thus, further increase the interval of overlap. However, we also note that if future observations of light element abundances find that $\Omega_b h^2 \lsim 0.018$, the range of concordance in this simple mixed dark matter model vanishes., Comment: 12 pages g-zipped, uuencoded postscript. Figures available at ftp://astro.uchicago.edu/pub/astro/russell/x-ray_bbn/ or at http://astro.uchicago.edu/home/web/russell/research/cosmology/Omega_b/

The \HOmega\ diagram is resurrected to dramatically illustrate the nature of the key problems in physical cosmology today and the role that nuclear physics plays in many of them. In particular it is noted that the constraints on \OmegaB\ from big bang nucleosynthesis do not overlap with the constraints on \OmegaVis\ nor have significant overlap with the lower bound on $��$ from cluster studies. The former implies that the bulk of the baryons are dark and the later is the principle argument for non-baryonic dark matter. A comparison with hot x-ray emitting gas in clusters is also made. The lower bound on the age of the universe from globular cluster ages (hydrogen burning in low mass stars) and from nucleocosmochronology also illustrates the Hubble constant requirement $H_0 \le 66 \Hunits$ for $��_0 = 1$\@. It is also noted that high values of $H_0$ ($\sim 80\Hunits$) even more strongly require the presence of non-baryonic dark matter. The lower limit on $H_0$ ($\ge 38\Hunits$) from carbon detonation driven type~Ia supernova constrains long ages and only marginally allows \OmegaB\ to overlap with \OmegaClus. Diagrams of \HOmega\ for $��_0=0$ and $��_0\neq 0$ are presented to show that the need for non-baryonic dark matter is independent of $��$., 10 pages, LaTeX(2.09), 4 figures. A nicely formatted postscript version of the text with encapsulated figures can be found at ftp://astro.uchicago.edu/pub/astro/HOmega (see the README file for details)

We investigate the possibility that inhomogeneous nucleosynthesis may eventually be used to explain the abundances of \li6, \be9 and B in population II stars. The present work differs from previous studies in that we have used a more extensive reaction network. It is demonstrated that in the simplest scenario the abundances of the light elements with $A\le7$ constrain the separation of inhomogeneities to sufficiently small scales that the model is indistinguishable from homogeneous nucleosynthesis and that the abundances of \li6, \be9\ and B are then below observations by several orders of magnitude. This conclusion does not depend on the \li7 constraint. We also examine alternative scenarios which involve a post-nucleosynthesis reprocessing of the light elements to reproduce the observed abundances of Li and B, while allowing for a somewhat higher baryon density (still well below the cosmological critical density). Future B/H measurements may be able to exclude even this exotic scenario and further restrict primordial nucleosynthesis to approach the homogeneous model conclusions., 18 pages; Plain TeX; UMN-TH-1131/93