33,024 research outputs found
Tracking The Post-BBN Evolution Of Deuterium
The primordial abundance of deuterium produced during Big Bang
Nucleosynthesis (BBN) depends sensitively on the universal ratio of baryons to
photons, an important cosmological parameter probed independently by the Cosmic
Microwave Background (CMB) radiation. Observations of deuterium in
high-redshift, low-metallicity QSO Absorption Line Systems (QSOALS) provide a
key baryometer, determining the baryon abundance at the time of BBN to a
precision of 5%. Alternatively, if the CMB-determined baryon to photon ratio is
used in the BBN calculation of the primordial abundances, the BBN-predicted
deuterium abundance may be compared with the primordial value inferred from the
QSOALS, testing the standard cosmological model. In the post-BBN universe, as
gas is cycled through stars, deuterium is only destroyed so that its abundance
measured anytime, anywhere in the Universe, bounds the primordial abundance
from below. Constraints on models of post-BBN Galactic chemical evolution
follow from a comparison of the relic deuterium abundance with the
FUSE-inferred deuterium abundances in the chemically enriched, stellar
processed material of the local ISM.Comment: 8 pages, 5 figures, to appear in the Proceedings of the Future
Directions in Ultraviolet Spectroscopy Conferenc
Effect of Long-lived Strongly Interacting Relic Particles on Big Bang Nucleosynthesis
It has been suggested that relic long-lived strongly interacting massive
particles (SIMPs, or particles) existed in the early universe. We study
effects of such long-lived unstable SIMPs on big bang nucleosynthesis (BBN)
assuming that such particles existed during the BBN epoch, but then decayed
long before they could be detected. The interaction strength between an
particle and a nucleon is assumed to be similar to that between nucleons. We
then calculate BBN in the presence of the unstable neutral charged
particles taking into account the capture of particles by nuclei to form
-nuclei. We also study the nuclear reactions and beta decays of -nuclei.
We find that SIMPs form bound states with normal nuclei during a relatively
early epoch of BBN. This leads to the production of heavy elements which remain
attached to them. Constraints on the abundance of particles during BBN
are derived from observationally inferred limits on the primordial light
element abundances. Particle models which predict long-lived colored particles
with lifetimes longer than 200 s are rejected based upon these
constraints.Comment: 19 pages, 4 figure
Weak Interaction Rate Coulomb Corrections in Big Bang Nucleosynthesis
We have applied a fully relativistic Coulomb wave correction to the weak
reactions in the full Kawano/Wagoner Big Bang Nucleosynthesis (BBN) code. We
have also added the zero temperature radiative correction. We find that using
this higher accuracy Coulomb correction results in good agreement with previous
work, giving only a modest 0.04 percent increase in helium mass fraction over
correction prescriptions applied previously in BBN calculations. We have
calculated the effect of these corrections on other light element abundance
yields in BBN and we have studied these yields as functions of electron
neutrino lepton number. This has allowed insights into the role of the Coulomb
correction in the setting of the neutron-to-proton ratio during the BBN epoch.
We find that the lepton capture processes' contributions to this ratio are only
second order in the Coulomb correction.Comment: 8 pages, 3 figure
BBN For Pedestrians
The simplest, `standard' model of Big Bang Nucleosynthesis (SBBN) assumes
three light neutrinos (N_nu = 3) and no significant electron neutrino
asymmetry, leaving only one adjustable parameter: the baryon to photon ratio
eta. The primordial abundance of any one nuclide can, therefore, be used to
measure the baryon abundance and the value derived from the observationally
inferred primordial abundance of deuterium closely matches that from current,
non-BBN data, primarily from the WMAP survey. However, using this same estimate
there is a tension between the SBBN-predicted 4He and 7Li abundances and their
current, observationally inferred primordial abundances, suggesting that N_nu
may differ from the standard model value of three and/or that there may be a
non-zero neutral lepton asymmetry (or, that systematic errors in the abundance
determinations have been underestimated or overlooked). The differences are not
large and the allowed ranges of the BBN parameters permitted by the data are
quite small. Within these ranges, the BBN-predicted abundances of D, 3He, 4He,
and 7Li are very smooth, monotonic functions of eta, N_nu, and the lepton
asymmetry. It is possible to describe the dependencies of these abundances (or
powers of them) upon the three parameters by simple, linear fits which, over
their ranges of applicability, are accurate to a few percent or better. The
fits presented here have not been maximized for their accuracy but, for their
simplicity. To identify the ranges of applicability and relative accuracies,
they are compared to detailed BBN calculations; their utility is illustrated
with several examples. Given the tension within BBN, these fits should prove
useful in facilitating studies of the viability of proposals for non-standard
physics and cosmology, prior to undertaking detailed BBN calculations.Comment: Submitted to a Focus Issue on Neutrino Physics in New Journal of
Physics (www.njp.org
Neutrinos And Big Bang Nucleosynthesis
According to the standard models of particle physics and cosmology, there
should be a background of cosmic neutrinos in the present Universe, similar to
the cosmic microwave photon background. The weakness of the weak interactions
renders this neutrino background undetectable with current technology. The
cosmic neutrino background can, however, be probed indirectly through its
cosmological effects on big bang nucleosynthesis (BBN) and the cosmic microwave
background (CMB) radiation. In this BBN review, focused on neutrinos and, more
generally on dark radiation, the BBN constraints on the number of "equivalent
neutrinos" (dark radiation), on the baryon asymmetry (baryon density), and on a
possible lepton asymmetry (neutrino degeneracy) are reviewed and updated. The
BBN constraints on dark radiation and on the baryon density following from
considerations of the primordial abundances of deuterium and helium-4 are in
excellent agreement with the complementary results from the CMB, providing a
suggestive, but currently inconclusive, hint of the presence of dark radiation
and, they constrain any lepton asymmetry. For all the cases considered here
there is a "lithium problem": the BBN-predicted lithium abundance exceeds the
observationally inferred primordial value by a factor of ~3.Comment: Invited Review article for the Special Issue on Neutrino Physics,
Advances in High Energy Physics, 25 pages, 10 figure
Hiding relativistic degrees of freedom in the early universe
We quantify the extent to which extra relativistic energy density can be
concealed by a neutrino asymmetry without conflicting with the baryon asymmetry
measured by the Wilkinson Microwave Anisotropy Probe (WMAP). In the presence of
a large electron neutrino asymmetry, slightly more than seven effective
neutrinos are allowed by Big Bang Nucleosynthesis (BBN) and WMAP at 2\sigma.
The same electron neutrino degeneracy that reconciles the BBN prediction for
the primordial helium abundance with the observationally inferred value also
reconciles the LSND neutrino with BBN by suppressing its thermalization prior
to BBN.Comment: 5 pages, 5 figure
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