Rothman and Matzner
[140]
considered primordial nucleosynthesis in anisotropic
cosmologies, solving the strong reaction equations leading to
. They find that the concentration of
increases with increasing shear 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
[109]
extended this work to include 30 strong 2-particle reactions
involving nuclei with mass numbers
, and to demonstrate the effects of anisotropy on the
cosmologically significant isotopes
,
,
and
as a function of the baryon to photon ratio. They conclude that
the effect of anisotropy on
and
is not significant, and the abundances of
and
increase with anisotropy in accord with
[140]
.
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
compared to a homogeneous model. However, plane symmetric,
general relativistic simulations with neutron diffusion
[110]
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.
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