381 research outputs found
Did the Universe start at Zero Metallicity?
Standard Big Bang nucleosynthesis predicts an essentially zero primordial
metallicity. I speculate on possible metal (i.e. nucleon number A\geq 12)
production in scenarios of inhomogeneous Big Bang nucleosynthesis. It is
conceivable, though not necessarily probable, that some primordial metallicity
is synthesized if a small fraction of all cosmic baryons reside in very
high-density regions. Such conditions could possibly result from the
evaporation of some baryon-number carrying soliton prior to the epoch of Big
Bang nucleosynthesis.Comment: 4 pages, to appear in proceedings of The First Stars meeting, held in
Garching, Germany, August 199
Baryon Number Transport in a Cosmic QCD-Phase Transition
We investigate the transport of baryon number across phase boundaries in a
putative first order QCD-phase transition. Two independent phenomenological
models are employed to estimate the baryon penetrability at the phase boundary:
chromoelectric flux tube models; and an analogy to baryon-baryon coalescence in
nuclear physics. Our analysis indicates that baryon transport across phase
boundaries may be order of magnitude more efficient than other work has
suggested. We discuss the substantial uncertainties involved in estimating
baryon penetrability at phase boundaries.Comment: 25 pages, 4 figures (available upon request by mail or fax), plain
tex, UCRL-JC-00000
The Cloud-in-Cloud Problem in the Press-Schechter Formalism of Hierarchical Structure Formation
The formalism by Press and Schechter (PS) is often used to infer number
densities of virialized objects of mass M (e.g. quasars, galaxies, clusters of
galaxies, etc.) from a count of initially overdense regions in a Gaussian
density perturbation field. We reanalyze the PS-formalism by explicitly
counting underdense regions which are embedded within overdense regions, so
called cloud-in-clouds. In contrast to the original PS-formalism, our revised
analysis automatically accounts for all the cosmic material. We find that mass
distribution functions for virialized objects are altered by the proper
solution of the cloud-in-cloud problem. These altered distribution functions
agree much better with distribution functions inferred form N-body simulations
than the original PS-distribution functions.Comment: 13 pages, 4 figures (available upon request by mail or fax), plain
te
Absence of a Lower Limit on Omega_b in Inhomogeneous Primordial Nucleosynthesis
We show that a class of inhomogeneous big bang nucleosynthesis models exist
which yield light-element abundances in agreement with observational
constraints for baryon-to-photon ratios significantly smaller than those
inferred from standard homogeneous big bang nucleosynthesis (HBBN). These
inhomogeneous nucleosynthesis models are characterized by a bimodal
distribution of baryons in which some regions have a local baryon-to-photon
ratio eta=3*10e-10, while the remaining regions are baryon-depleted. HBBN
scenarios with primordial (2H+3He)/H<9*10e-5 necessarily require that most
baryons be in a dark or non-luminous form, although new observations of a
possible high deuterium abundance in Lyman-alpha clouds may relax this
requirement somewhat. The models described here present another way to relax
this requirement and can even eliminate any lower bound on the baryon-to-photon
ratio.Comment: 13 pages, 2 figures (available upon request by email), plain te
Delayed Reheating and the Breakdown of Coherent Oscillations
We analyze the evolution of the perturbations in the inflaton field and
metric following the end of inflation. We present accurate analytic
approximations for the perturbations, showing that the coherent oscillations of
the post-inflationary condensate necessarily break down long before any current
phenomenological constraints require the universe to become radiation
dominated. Further, the breakdown occurs on length-scales equivalent to the
comoving post-inflationary horizon size. This work has implications for both
the inflationary "matching" problem, and the possible generation of a
stochastic gravitational wave background in the post-inflationary universe.Comment: 18 pages, 5 figures, v2: references added, extended discussion in
section
Enhanced Heavy-Element Formation in Baryon-Inhomogeneous Big-Bang Models
We show that primordial nucleosynthesis in baryon inhomogeneous big-bang
models can lead to significant heavy-element production while still satisfying
all the light-element abundance constraints including the low lithium abundance
observed in population II stars. The parameters which admit this solution arise
naturally from the process of neutrino induced inflation of baryon
inhomogeneities prior to the epoch of nucleosynthesis. These solutions entail a
small fraction of baryons (\le 2\%) in very high density regions with local
baryon-to-photon ratio , while most baryons are at a
baryon-to-photon ratio which optimizes the agreement with light-element
abundances. The model would imply a unique signature of baryon inhomogeneities
in the early universe, evidenced by the existence of primordial material
containing heavy-element products of proton and alpha- burning reactions with
an abundance of .Comment: 19 pages in plain Tex, 5 figures (not included) available by fax or
mail upon request, ApJ in press, L
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