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Production of heavy elements in inhomogeneous cosmologies
Rauscher, Thomas; Applegate, James H.; Cowan, John J.; Thielemann, Friedrich-Karl; Wiescher, Michael
AA(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA), AB(Department of Astronomy, Columbia University, New York, NY 10027), AC(Department of Physics and Astronomy, University of Oklahoma, Norma, OK 73019; Department of Astronomy, Columbia University, New York, NY 10027), AD(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; Institut fur Theoretische Physik, Klingelbergstrasse 82, Universtat Basel, CH-4046 Basel, Switzerland), AE(Department of Physics, University of Notre Dame, Notre Dame, IN 46556)
The Astrophysical Journal, vol. 429, no. 2, pt. 1, p. 499-530 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Abundance, Astronomical Models, Baryons, Big Bang Cosmology, Density (Mass/Volume), Heavy Elements, Inhomogeneity, Nuclear Fusion, Reaction Products, Capture Effect, Convection-Diffusion Equation, Neutrons, Numerical Analysis
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Baryon density inhomogeneities during big bang nucleosynthesis can result from a variety of possible causes (e.g., quantum chromodynamic and electroweak phase transitions; cosmic strings). We present here the consequences of such inhomogeneities with special emphasis on the production of heavy elements in a parameter study, varying the global baryon-to-photon ratio eta (which is related to the baryon density and the Hubble constant via eta10 = 64.94 Omegab(H0/50)2 and the length scale of the density inhomogeneities. The production of heavy elements beyond Fe can only occur in neutron-rich environments; thus, we limit our study to neutron-rich zones, originating from neutron diffusion into low-density regions. In this first calculation including elements heavier than Si, we prove an earlier hypothesis that under such conditions r-process elements can be produced, strongly enhanced by the process of fission cycling. Primordial r-process abundances are, however, very sensitive to the choice of eta. Significant amounts, comparable to or larger than the (permitted) floor of heavy-element abundances found in low-metallicity stars at the onset of galactic evolution, can only be obtained for values in excess of eta10 = 133 (i.e., Omegab(h50)2 = 2.0; e.g., Omegab = 1, H0 = 71, or Omegab = 0.5, H0 = 100) and large length scales of inhomogeneities, which minimize the back-diffusion of neutrons into proton-rich regions. Recent investigations analyzing the primordial abundances of light elements seem to set tighter limits, eta10 less than 26 to 39 (Omega b)(h50)2 less than 0.4 to 0.6, from He-4 and apparently considerably lower values based on Li, Be, and B. Under such conditions the predicted abundances of heavy elements are a factor of 105 or more below presently observable limits.

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