Nucleosynthesis in the Presence of Primordial Isocurvature Baryon Fluctuations
Abstract
We study big bang nucleosynthesis in the presence of large mass scale, nonlinear entropy fluctuations. Overdense regions, with masses above the local baryon Jeans mass, are expected to collapse and form condensed objects. Surviving nucleosynthesis products therefore tend to originate from underdense regions. We compute expected survival lightelement (^{2}H, ^{3}He, ^{4}He, and ^{7}Li) abundance yields for a variety of stochastic fluctuation spectra. In general, we find that spectra with significant power in fluctuations on mass scales below that of the local baryon Jeans mass (∼10^{5} M_{sun}) produce nucleosynthesis yields which are in conflict with observationally inferred primordial abundances. Only when this smallscale structure is absent or suppressed, and the collapse efficiency of overdense regions is high, can there exist a range of fluctuation spectral characteristics which conceivably could meet all primordial abundance constraints. Even then, the primordial abundance of ^{7}Li would have to be larger than ^{7}Li/H ≍ 3 × 10^{10}. In such models, abundance constraints could be met even when the precollapse baryonic fraction of the closure density is Ω_{b} ≍ 0.2 h^{2} (h is the Hubble parameter in units of 100 km s^{1} Mpc^{1}). Nucleosynthesis in these models is characterized by high ^{2}H/H and low ^{4}He mass fraction relative to a homogeneous big bang at a given value of Ω_{b} h^{2}. A potentially observable signature of these models is the production of intrinsic primordial abundance variations on baryon mass scales up to 10^{10}10^{12} M_{sun}.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 1995
 DOI:
 10.1086/176278
 arXiv:
 arXiv:astroph/9410027
 Bibcode:
 1995ApJ...452...33J
 Keywords:

 COSMOLOGY: LARGESCALE STRUCTURE OF UNIVERSE;
 COSMOLOGY: EARLY UNIVERSE;
 COSMOLOGY: THEORY;
 NUCLEAR REACTIONS;
 NUCLEOSYNTHESIS;
 ABUNDANCES;
 Astrophysics
 EPrint:
 40 pages with 17 figures (figures available upon request), plain Tex