3.5 Plane Symmetric Gravitational Waves3 RELATIVISTIC COSMOLOGY3.3 Quark-Hadron Phase Transition

3.4 Nucleosynthesis 

Observations of the light elements produced during Big Bang nucleosynthesis following the quark/hadron phase transition (roughly image - image seconds after the Big Bang) are in good agreement with the standard model of our Universe (see § 2.2). However, it is interesting to investigate other more general models to assert the role of shear and curvature on the nucleosynthesis process.

Rothman and Matzner [48Jump To The Next Citation Point In The Article] considered primordial nucleosynthesis in anisotropic cosmologies, solving the strong reaction equations leading to image He. They find that the concentration of image He increases with increasing shear; this is due to time scale effects and the competition between dissipation and enhanced reaction rates from photon heating and neutrino blue shifts. Their results have been used to place a limit on anisotropy at the epoch of nucleosynthesis. Kurki-Suonio and Matzner [38] extended this work to include 30 strong 2-particle reactions involving nuclei with mass numbers image, and to demonstrate the effects of anisotropy on the cosmologically significant isotopes image H, image He, image He and image Li as a function of the baryon to photon ratio. They conclude that the effect of anisotropy on image H and image He is not significant, and the abundances of image He and image Li increase with anisotropy in accord with [48].

Furthermore, it is possible that neutron diffusion, the process whereby neutrons diffuse out from regions of very high baryon density just before nucleosynthesis, can affect the neutron to proton ratio in such a way as to enhance deuterium and reduce image He compared to a homogeneous model. However, plane symmetric, general relativistic simulations with neutron diffusion [39] show that the neutrons diffuse back into the high density regions once nucleosynthesis begins there - thereby wiping out the effect. As a result, although inhomogeneities influence the element abundances, they do so at a much smaller degree then previously speculated. The numerical simulations also demonstrate that, because of the back diffusion, a cosmological model with a critical baryon density cannot be made consistent with helium and deuterium observations, even with substantial baryon inhomogeneities and the anticipated neutron diffusion effect.



3.5 Plane Symmetric Gravitational Waves3 RELATIVISTIC COSMOLOGY3.3 Quark-Hadron Phase Transition

image Computational Cosmology: from the Early Universe to the Large Scale Structure
Peter Anninos
http://www.livingreviews.org/lrr-1998-9
© Max-Planck-Gesellschaft. ISSN 1433-8351
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