284 research outputs found
A Simple Way of Calculating Cosmological Relic Density
A simple procedure is presented which leads to a dramatic simplification in
the calculation of the relic density of stable particles in the Universe.Comment: 7 pages in LaTex, no figures; University of Michigan preprint
UM-TH-94-02 (February 1994). Changes: a coefficient in (Eq. 16)
corrected; added Acknowledgements and revised Note Added; plain LaTex only
(no need to use RevTex
Protecting the Baryon Asymmetry with Thermal Masses
We consider the evolution of baryon number in the early universe under
the influence of rapid sphaleron interactions and show that will remain
nonzero at all times even in the case of . This result arises due to
thermal Yukawa interactions that cause nonidentical dispersion relations
(thermal masses) for different lepton families. We point out the relevance of
our result to the Affleck-Dine type baryogenesis.Comment: 11pp., plain tex, UMN-TH-1248/94, CfPA-TH-94-1
Mapping systematic errors in helium abundance determinations using Markov Chain Monte Carlo
Monte Carlo techniques have been used to evaluate the statistical and
systematic uncertainties in the helium abundances derived from extragalactic
H~II regions. The helium abundance is sensitive to several physical parameters
associated with the H~II region. In this work, we introduce Markov Chain Monte
Carlo (MCMC) methods to efficiently explore the parameter space and determine
the helium abundance, the physical parameters, and the uncertainties derived
from observations of metal poor nebulae. Experiments with synthetic data show
that the MCMC method is superior to previous implementations (based on flux
perturbation) in that it is not affected by biases due to non-physical
parameter space. The MCMC analysis allows a detailed exploration of
degeneracies, and, in particular, a false minimum that occurs at large values
of optical depth in the He~I emission lines. We demonstrate that introducing
the electron temperature derived from the [O~III] emission lines as a prior, in
a very conservative manner, produces negligible bias and effectively eliminates
the false minima occurring at large optical depth. We perform a frequentist
analysis on data from several "high quality" systems. Likelihood plots
illustrate degeneracies, asymmetries, and limits of the determination. In
agreement with previous work, we find relatively large systematic errors,
limiting the precision of the primordial helium abundance for currently
available spectra.Comment: 25 pages, 11 figure
Effective degrees of freedom during the radiation era
We update the curves of the effective degrees of freedom for the energy
density and for the entropy density during the era of
radiation domination in the Universe. We find that a plain count of effective
degrees of freedom sets an upper limit to the temperature of the quark-hadron
transition at MeV for the energy density and MeV for the
entropy density.Comment: 3 pages, 2 figure
Lattice QCD Impact on Determination of the CKM Matrix
We review many lattice QCD calculations that impact the precise determination
of the CKM matrix. We focus on decay constants and semileptonic form factors of
both light ( and K) and heavy-light ( and ) mesons.
Implication of form factors will be shown. When combined with
experimental results for branching fractions and differential decay rates, the
above calculations strongly constrain the first two rows of the CKM matrix. We
discuss a long standing difference between and as
determined from exclusive or inclusive decays.Comment: 10 pages, 6 figures, Proceedings of 16th Conference on Flavor Physics
and CP Violation (FPCP 2018), July 14-18, 2018, Hyderabad, Indi
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
Light Unstable Sterile Neutrino
The three massless active (doublet) neutrinos may mix with two heavy and one
\underline {light} sterile (singlet) neutrinos so that the induced masses and
mixings among the former are able to explain the present data on atmospheric
and solar neutrino oscillations. If the LSND result is also to be explained,
one active neutrino mass eigenstate must mix with the light sterile neutrino. A
specific model is proposed with the spontaneous and soft explicit breaking of a
new global symmetry so that a sterile neutrino will decay into an
active antineutrino and a nearly massless pseudo-Majoron.Comment: Discussion and references adde
Big Bang Nucleosynthesis with Gaussian Inhomogeneous Neutrino Degeneracy
We consider the effect of inhomogeneous neutrino degeneracy on Big Bang
nucleosynthesis for the case where the distribution of neutrino chemical
potentials is given by a Gaussian. The chemical potential fluctuations are
taken to be isocurvature, so that only inhomogeneities in the electron chemical
potential are relevant. Then the final element abundances are a function only
of the baryon-photon ratio , the effective number of additional neutrinos
, the mean electron neutrino degeneracy parameter , and
the rms fluctuation of the degeneracy parameter, . We find that for
fixed , , and , the abundances of helium-4,
deuterium, and lithium-7 are, in general, increasing functions of .
Hence, the effect of adding a Gaussian distribution for the electron neutrino
degeneracy parameter is to decrease the allowed range for . We show that
this result can be generalized to a wide variety of distributions for .Comment: 9 pages, 3 figures, added discussion of neutrino oscillations,
altered presentation of figure
A New Approach to Systematic Uncertainties and Self-Consistency in Helium Abundance Determinations
Tests of big bang nucleosynthesis and early universe cosmology require
precision measurements for helium abundance determinations. However, efforts to
determine the primordial helium abundance via observations of metal poor H II
regions have been limited by significant uncertainties. This work builds upon
previous work by providing an updated and extended program in evaluating these
uncertainties. Procedural consistency is achieved by integrating the hydrogen
based reddening correction with the helium based abundance calculation, i.e.,
all physical parameters are solved for simultaneously. We include new atomic
data for helium recombination and collisional emission based upon recent work
by Porter et al. and wavelength dependent corrections to underlying absorption
are investigated. The set of physical parameters has been expanded here to
include the effects of neutral hydrogen collisional emission. Because of a
degeneracy between the solutions for density and temperature, the precision of
the helium abundance determinations is limited. Also, at lower temperatures (T
\lesssim 13,000 K) the neutral hydrogen fraction is poorly constrained
resulting in a larger uncertainty in the helium abundances. Thus the derived
errors on the helium abundances for individual objects are larger than those
typical of previous studies. The updated emissivities and neutral hydrogen
correction generally raise the abundance. From a regression to zero
metallicity, we find Y_p as 0.2561 \pm 0.0108, in broad agreement with the WMAP
result. Tests with synthetic data show a potential for distinct improvement,
via removal of underlying absorption, using higher resolution spectra. A small
bias in the abundance determination can be reduced significantly and the
calculated helium abundance error can be reduced by \sim 25%.Comment: 51 pages, 13 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
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