Resolving the Helium Lyman-α\alpha Forest: Mapping Intergalactic Gas and Ionizing Radiation at z≈3z\approx 3

We present a new, high resolution HST/GHRS spectrum of quasar Q0302-003, and use the HeII Lyman-$\alpha$ absorption, together with a high resolution Keck spectrum of the HI Lyman-$\alpha$ forest, to probe the distribution and ionization state of foreground gas just below the quasar redshift $z\approx 3.3$. The main new conclusions from the current data are: 1. The HeII Lyman-$\alpha$ forest is detected; 2. The ``diffuse'' (redshift-space-filling) medium is also detected, and must have a low density ($\Omega\le 0.01 (h/0.7)^{-3/2}$) consistent with standard primordial nucleosynthesis and models of early gas collapse into protogalaxies; 3. The intergalactic ionizing spectrum is soft ($\eta\ge 100$), although the intergalactic helium is probably mostly doubly ionized by $z=3.3$; 4. The helium abundance is within a factor of a few of standard Big Bang predictions, over a large volume of space at high redshift.Comment: AAS Latex, 3 figures, accepted for publication in the Astronomical Journa

Nuclear Reaction Rates and Primordial 6^6Li

We examine the possibility that Big Bang Nucleosynthesis (BBN) may produce non-trivial amounts of $^6$Li. If a primordial component of this isotope could be observed, it would provide a new fundamental test of Big-Bang cosmology, as well as new constraints on the baryon density of the universe. At present, however, theoretical predictions of the primordial $^6$Li abundance are extremely uncertain due to difficulties in both theoretical estimates and experimental determinations of the deuterium-plus-alpha radiative capture reaction cross-section. We also argue that present observational capabilities do not yet allow the detection of primeval $^6$Li in very metal-poor stars of the galactic halo. However, if the critical cross section is towards the upper end of its plausible range, then improvements in $^6$Li detection capabilities may allow the establishment of $^6$Li as another product of BBN. It is also noted that a primordial $^6$Li detection could help resolve current concerns about the extragalactic D/H determination.Comment: 10 pages, REVTeX, 5 PostScript figures with psfig. Submitted to Physical Review

Review of Particle Physics

This biennial review summarizes much of Particle Physics. Using data from previous editions, plus 1900 new measurements from 700 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. © 1996 The American Physical Society