83 research outputs found
Primordial Nucleosynthesis in the New Cosmology
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB)
anisotropies independently predict the universal baryon density. Comparing
their predictions will provide a fundamental test on cosmology. Using BBN and
the CMB together, we will be able to constrain particle physics, and predict
the primordial, light element abundances. These future analyses hinge on new
experimental and observational data. New experimental data on nuclear cross
sections will help reduce theoretical uncertainties in BBN's predictions. New
observations of light element abundances will further sharpen BBN's probe of
the baryon density. Observations from the MAP and PLANCK satellites will
measure the fluctuations in the CMB to unprecedented accuracy, allowing the
precise determination of the baryon density. When combined, this data will
present us with the opportunity to perform precision cosmology.Comment: 3 pages, 1 figure, for Nuclei in the Cosmos VII proceedings to appear
in Nuclear Physics
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
Cosmic Rays during BBN as Origin of Lithium Problem
There may be non-thermal cosmic rays during big-bang nucleosynthesis (BBN)
epoch (dubbed as BBNCRs). This paper investigated whether such BBNCRs can be
the origin of Lithium problem or not. It can be expected that BBNCRs flux will
be small in order to keep the success of standard BBN (SBBN). With favorable
assumptions on the BBNCR spectrum between 0.09 -- 4 MeV, our numerical
calculation showed that extra contributions from BBNCRs can account for the
Li abundance successfully. However Li abundance is only lifted an order
of magnitude, which is still much lower than the observed value. As the
deuteron abundance is very sensitive to the spectrum choice of BBNCRs, the
allowed parameter space for the spectrum is strictly constrained. We should
emphasize that the acceleration mechanism for BBNCRs in the early universe is
still an open question. For example, strong turbulent magnetic field is
probably the solution to the problem. Whether such a mechanism can provide the
required spectrum deserves further studies.Comment: 34 pages, 21 figures, published versio
Big bang nucleosynthesis with a varying fine structure constant and non-standard expansion rate
We calculate primordial abundances of light elements produced during big bang
nucleosynthesis when the fine structure constant and/or the cosmic expansion
rate take non-standard values. We compare them with the recent values of
observed D, He4 and Li7 abundances, which show slight inconsistency among
themselves in the standard big bang nucleosynthesis scenario. This
inconsistency is not solved by considering either a varying fine structure
constant or a non-standard expansion rate separately but solutions are found by
their simultaneous existence.Comment: 5 pages, 5 figure
Solar Neutrino Constraints on the BBN Production of Li
Using the recent WMAP determination of the baryon-to-photon ratio, 10^{10}
\eta = 6.14 to within a few percent, big bang nucleosynthesis (BBN)
calculations can make relatively accurate predictions of the abundances of the
light element isotopes which can be tested against observational abundance
determinations. At this value of \eta, the Li7 abundance is predicted to be
significantly higher than that observed in low metallicity halo dwarf stars.
Among the possible resolutions to this discrepancy are 1) Li7 depletion in the
atmosphere of stars; 2) systematic errors originating from the choice of
stellar parameters - most notably the surface temperature; and 3) systematic
errors in the nuclear cross sections used in the nucleosynthesis calculations.
Here, we explore the last possibility, and focus on possible systematic errors
in the He3(\alpha,\gamma)Be7 reaction, which is the only important Li7
production channel in BBN. The absolute value of the cross section for this key
reaction is known relatively poorly both experimentally and theoretically. The
agreement between the standard solar model and solar neutrino data thus
provides additional constraints on variations in the cross section (S_{34}).
Using the standard solar model of Bahcall, and recent solar neutrino data, we
can exclude systematic S_{34} variations of the magnitude needed to resolve the
BBN Li7 problem at > 95% CL. Additional laboratory data on
He3(\alpha,\gamma)Be7 will sharpen our understanding of both BBN and solar
neutrinos, particularly if care is taken in determining the absolute cross
section and its uncertainties. Nevertheless, it already seems that this
``nuclear fix'' to the Li7 BBN problem is unlikely; other possible solutions
are briefly discussed.Comment: 21 pages, 3 ps figure
Cosmological bounds on pseudo Nambu-Goldstone bosons
We review the cosmological implications of a relic population of pseudo
Nambu-Goldstone bosons (pNGB) with an anomalous coupling to two photons, often
called axion-like particles (ALPs). We establish constraints on the pNGB mass
and two-photon coupling by considering big bang nucleosynthesis, the physics of
the cosmic microwave background, and the diffuse photon background. The bounds
from WMAP7 and other large-scale-structure data on the effective number of
neutrino species can be stronger than the traditional bounds from the
primordial helium abundance. These bounds, together with those from primordial
deuterium abundance, constitute the most stringent probes of early decays.Comment: 29 pages, 13 pictures. Enlarged discussions on BBN and recombination
constraints. One figure and several references added. Version accepted in
JCA
Constraining the variation of the coupling constants with big bang nucleosynthesis
We consider the possibility of the coupling constants of the gauge interactions at the time of big bang nucleosynthesis
having taken different values from what we measure at present, and investigate
the allowed difference requiring the shift in the coupling constants not
violate the successful calculation of the primordial abundances of the light
elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a
model in which their relative variations are governed by a single scalar field,
dilaton, as found in string theory. The results include a limit on the fine
structure constant
, which is
two orders stricter than the limit obtained by considering the variation of
alone.Comment: 7 page
Nucleosynthesis Constraints on a Massive Gravitino in Neutralino Dark Matter Scenarios
The decays of massive gravitinos into neutralino dark matter particles and
Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may
alter the primordial light-element abundances. We present here details of a new
suite of codes for evaluating such effects, including a new treatment based on
PYTHIA of the evolution of showers induced by hadronic decays of massive,
unstable particles such as a gravitino. We also develop an analytical treatment
of non-thermal hadron propagation in the early universe, and use this to derive
analytical estimates for light-element production and in turn on decaying
particle lifetimes and abundances. We then consider specifically the case of an
unstable massive gravitino within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM). We present upper limits on its
possible primordial abundance before decay for different possible gravitino
masses, with CMSSM parameters along strips where the lightest neutralino
provides all the astrophysical cold dark matter density. We do not find any
CMSSM solution to the cosmological Li7 problem for small m_{3/2}. Discounting
this, for m_{1/2} ~ 500 GeV and tan beta = 10 the other light-element
abundances impose an upper limit m_{3/2} n_{3/2}/n_\gamma < 3 \times 10^{-12}
GeV to < 2 \times 10^{-13} GeV for m_{3/2} = 250 GeV to 1 TeV, which is similar
in both the coannihilation and focus-point strips and somewhat weaker for tan
beta = 50, particularly for larger m_{1/2}. The constraints also weaken in
general for larger m_{3/2}, and for m_{3/2} > 3 TeV we find a narrow range of
m_{3/2} n_{3/2}/n_\gamma, at values which increase with m_{3/2}, where the Li7
abundance is marginally compatible with the other light-element abundances.Comment: 74 pages, 40 Figure
Do primordial Lithium abundances imply there's no Dark Energy?
Explaining the well established observation that the expansion rate of the
universe is apparently accelerating is one of the defining scientific problems
of our age. Within the standard model of cosmology, the repulsive 'dark energy'
supposedly responsible has no explanation at a fundamental level, despite many
varied attempts. A further important dilemma in the standard model is the
Lithium problem, which is the substantial mismatch between the theoretical
prediction for 7-Li from Big Bang Nucleosynthesis and the value that we observe
today. This observation is one of the very few we have from along our past
worldline as opposed to our past lightcone. By releasing the untested
assumption that the universe is homogeneous on very large scales, both apparent
acceleration and the Lithium problem can be easily accounted for as different
aspects of cosmic inhomogeneity, without causing problems for other
cosmological phenomena such as the cosmic microwave background. We illustrate
this in the context of a void model.Comment: 14 pages, 4 figures. v2: minor rearrangements in the text, comments
and references expanded, results unchange
Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons
We study the effect on the cosmic microwave background (CMB) anisotropy and
large scale structure (LSS) power spectrum of a scattering interaction between
cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS
spectrum through momentum transfer between the cold dark matter particles and
the baryons. We find that current CMB observations can put an upper limit on
the scattering cross section which is comparable with or slightly stronger than
previous disk heating constraints at masses greater than 1 GeV, and much
stronger at smaller masses. When large-scale structure constraints are added to
the CMB limits, our constraint is more stringent than this previous limit at
all masses. In particular, a dark matter-baryon scattering cross section
comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark
matter mass greater than 1 GeV.Comment: 8 pages, 2 figures, use RevTeX4, submitted to PRD replaced with
revised versio
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