314 research outputs found
Neutron Diffusion and Nucleosynthesis in an Inhomogeneous Big Bang Model
This article presents an original code for Big Bang Nucleosynthesis in a
baryon inhomogeneous model of the universe. In this code neutron diffusion
between high and low baryon density regions is calculated simultaneously with
the nuclear reactions and weak decays that compose the nucleosynthesis process.
The size of the model determines the time when neutron diffusion becomes
significant. This article describes in detail how the time of neutron diffusion
relative to the time of nucleosynthesis affects the final abundances of He4,
deuterium and Li7. These results will be compared with the most recent
observational constraints of He4, deuterium and Li7. This inhomogeneous model
has He4 and deuterium constraints in concordance for baryon to photon ratio eta
= (4.3 - 12.3) X 10^{-10} Li7 constraints are brought into concordance with the
other isotope constraints by including a depletion factor as high as 5.9. These
ranges for the baryon to photon ratio and for the depletion factor are larger
than the ranges from a Standard Big Bang Nucleosynthesis model.Comment: 7/15, added reference
The Primordial Abundance of He4: An Update
We include new data in an updated analysis of helium in low metallicity
extragalactic HII regions with the goal of deriving the primordial abundance of
He4 (Y_P). We show that the new observations of Izotov et al (ITL) are
consistent with previous data. However they should not be taken in isolation to
determine (Y_P) due to the lack of sufficiently low metallicity points. We use
the extant data in a semi-empirical approach to bounding the size of possible
systematic uncertainties in the determination of (Y_P). Our best estimate for
the primordial abundance of He4 assuming a linear relation between He4 and O/H
is Y_P = 0.230 \pm 0.003 (stat) based on the subset of HII regions with the
lowest metallicity; for our full data set we find Y_P = 0.234 \pm 0.002 (stat).
Both values are entirely consistent with our previous results. We discuss the
implications of these values for standard big bang nucleosynthesis (SBBN),
particularly in the context of recent measurements of deuterium in high
redshift, low metallicity QSO absorption-line systems.Comment: 26 pages, latex, 6 ps figure
Primordial Nucleosynthesis as a test of variable rest masses 5-dimensional cosmology
The deviation of primordial Helium production due to a variation on the
difference between the rest masses of the nucleons is presented. It is found an
upper bound \delta (M_{_n} - M_{_p}) \alt 0.129 MeV, between the present and
nucleosynthesis epochs. This bound is used to analyze Wesson's theory of
gravitation; as a result, it is ruled out by observation.Comment: Corrected version with referee's remarks. Unchanged global results.
Some references added; to be published in Phys. Lett. A
Non-thermal leptogenesis and gravitino problem in inflaton decay
In the present work we discuss baryon asymmetry in the non-thermal
leptogenesis scenario and gravitino cosmology for an unstable gravitino with
inflaton decay. We take into account two production mechanisms for gravitino,
namely thermal production and inflaton decay. We wish to show in plots the
allowed parameter space so that the BBN constraint and the requirement for the
right baryon asymmetry are satisfied at the same time. However our analysis
shows that it is impossible to achieve both goals simultaneously.Comment: 11 pages, 1 figur
Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud
The primordial abundances of light elements produced in the standard theory
of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to
photons, a quantity inferred from observations of the microwave background. The
predicted primordial 7Li abundance is four times that measured in the
atmospheres of Galactic halo stars. This discrepancy could be caused by
modification of surface lithium abundances during the stars' lifetimes or by
physics beyond the Standard Model that affects early nucleosynthesis. The
lithium abundance of low-metallicity gas provides an alternative constraint on
the primordial abundance and cosmic evolution of lithium that is not
susceptible to the in situ modifications that may affect stellar atmospheres.
Here we report observations of interstellar 7Li in the low-metallicity gas of
the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun's
metallicity. The present-day 7Li abundance of the Small Magellanic Cloud is
nearly equal to the BBN predictions, severely constraining the amount of
possible subsequent enrichment of the gas by stellar and cosmic-ray
nucleosynthesis. Our measurements can be reconciled with standard BBN with an
extremely fine-tuned depletion of stellar Li with metallicity. They are also
consistent with non-standard BBN.Comment: Published in Nature. Includes main text and Supplementary
Information. Replaced with final title and abstrac
Cosmic Microwave Background Polarization
Cosmic microwave background (CMB) anisotropy is our richest source of
cosmological information; the standard cosmological model was largely
established thanks to study of the temperature anisotropies. By the end of the
decade, the Planck satellite will close this important chapter and move us
deeper into the new frontier of polarization measurements. Numerous
ground--based and balloon--borne experiments are already forging into this new
territory. Besides providing new and independent information on the primordial
density perturbations and cosmological parameters, polarization measurements
offer the potential to detect primordial gravity waves, constrain dark energy
and measure the neutrino mass scale. A vigorous experimental program is
underway worldwide and heading towards a new satellite mission dedicated to CMB
polarization.Comment: Review given at TAUP 2005; References added; Additional reference
Ribbons on the CBR Sky: A Powerful Test of a Baryon Symmetric Universe
If the Universe consists of domains of matter and antimatter, annihilations
at domain interfaces leave a distinctive imprint on the Cosmic Background
Radiation (CBR) sky. The signature is anisotropies in the form of long, thin
ribbons of width , separated by angle where L is the characteristic domain size, and
y-distortion parameter . Such a pattern could potentially be
detected by the high-resolution CBR anisotropy experiments planned for the next
decade, and such experiments may finally settle the question of whether or not
our Hubble volume is baryon symmetric.Comment: LaTeX, 10 pages, 4 figures in epsf. Revised version corrects a couple
of relevant mistake
Big Bang Nucleosynthesis in Crisis?
A new evaluation of the constraint on the number of light neutrino species
(N_nu) from big bang nucleosynthesis suggests a discrepancy between the
predicted light element abundances and those inferred from observations, unless
the inferred primordial 4He abundance has been underestimated by 0.014 +/-
0.004 (1 sigma) or less than 10% (95%C.L.) of 3He survives stellar processing.
With the quoted systematic errors in the observed abundances and a conservative
chemical evolution parameterization, the best fit to the combined data is N_nu
= 2.1 +/- 0.3 (1 sigma) and the upper limit is N_nu < 2.6 (95% C.L.). The data
are inconsistent with the Standard Model (N_nu = 3) at the 98.6% C.L.Comment: To be published in Phys. Rev. Lett. Revised version to reflect
referee comments and criticisms by Copi, Schramm, and Turner of robustness of
D/He-3 analysis. Small quantitative changes but qualitative conclusions
unchanged. Question mark added to title. Entire ps file available at
ftp://upenn5.hep.upenn.edu/pub/hata/papers/bbn.ps.Z See also astro-ph/941208
Effect of Finite Mass on Primordial Nucleosynthesis
We have calculated the small effect of finite nucleon mass on the
weak-interaction rates that interconvert protons and neutrons in the early
Universe. We have modified the standard code for primordial nucleosynthesis to
include these corrections and find a small, systematic increase in the 4He
yield, , depending slightly on the
baryon-to-photon ratio. The fractional changes in the abundances of the other
light elements are a few percent or less for interesting values of the
baryon-to-photon ratio.Comment: 15 pages, 8 figures, uses psfig.st
Characterising WIMPs at a future Linear Collider
We investigate the prospects for detecting and measuring the parameters of
WIMP dark matter in a model independent way at the International Linear
Collider. The signal under study is direct WIMP pair production with associated
initial state radiation . The analysis
accounts for the beam energy spectrum of the ILC and the dominant machine
induced backgrounds. The influence of the detector parameters are incorporated
by full simulation and event reconstruction within the framework of the ILD
detector concept. We show that by using polarised beams, the detection
potential is significantly increased by reduction of the dominant SM background
of radiative neutrino production . The
dominant sources of systematic uncertainty are the precision of the
polarisation measurement and the shape of the beam energy spectrum. With an
integrated luminosity of 500 fb the helicity structure of the interaction
involved can be inferred, and the masses and cross-sections can be measured
with a relative accuracy of the order of 1 %.Comment: 20 pages, 11 figure
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