6,220 research outputs found
Cosmological production of H_2 before the formation of the first galaxies
Previous calculations of the pregalactic chemistry have found that a small
amount of H_2, x[H_2]=n[H_2]/n[H] = 2.6e-6, is produced catalytically through
the H^-, H_2^+, and HeH^+ mechanisms. We revisit this standard calculation
taking into account the effects of the nonthermal radiation background produced
by cosmic hydrogen recombination, which is particularly effective at destroying
H^- via photodetachment. We also take into consideration the non-equilibrium
level populations of H_2^+, which occur since transitions among the
rotational-vibrational levels are slow compared to photodissociation. The new
calculation predicts a final H_2 abundance of x[H_2] = 6e-7 for the standard
cosmology. This production is due almost entirely to the H^- mechanism, with ~1
per cent coming from HeH^+ and ~0.004 per cent from H_2^+. We evaluate the
heating of the diffuse pregalactic gas from the chemical reactions that produce
H_2 and from rotational transitions in H_2, and find them to be negligible.Comment: 13 pages, 5 figures, MNRAS submitte
Sterile neutrino dark matter: A tale of weak interactions in the strong coupling epoch
We perform a detailed study of the weak interactions of standard model
neutrinos with the primordial plasma and their effect on the resonant
production of sterile neutrino dark matter. Motivated by issues in cosmological
structure formation on small scales, and reported X-ray signals that could be
due to sterile neutrino decay, we consider keV-scale sterile neutrinos.
Oscillation-driven production of such sterile neutrinos occurs at temperatures
MeV, where we study two significant effects of weakly charged
species in the primordial plasma: (1) the redistribution of an input lepton
asymmetry; (2) the opacity for active neutrinos. We calculate the
redistribution analytically above and below the quark-hadron transition, and
match with lattice QCD calculations through the transition. We estimate
opacities due to tree level processes involving leptons and quarks above the
quark-hadron transition, and the most important mesons below the transition. We
report final sterile neutrino dark matter phase space densities that are
significantly influenced by these effects, and yet relatively robust to
remaining uncertainties in the nature of the quark-hadron transition. We also
provide transfer functions for cosmological density fluctuations with cutoffs
at , that are relevant to galactic structure
formation.Comment: 28 pages, 11 figures, code repository at
https://github.com/ntveem/sterile-d
Nuclear Photoabsorption at Photon Energies between 300 and 850 Mev
We construct the formula for the photonuclear total absorption cross section
using the projection method and the unitarity relation. Our treatment is very
effective when interference effects in the absorption processes on a nucleon
are strong. The disappearance of the peak around the position of the
resonance in the nuclear photoabsorption can be explained with the cooperative
effect of the interference in two-pion production processes,the Fermi motion,
the collision broadenings of and , and the pion distortion in the
nuclear medium. The change of the interference effect by the medium plays an
important role.Comment: 22pages,7figures,revtex
Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile
We present results of theoretical study and numerical calculation of the
dynamics of molecular liquids based on combination of the memory equation
formalism and the reference interaction site model - RISM. Memory equations for
the site-site intermediate scattering functions are studied in the
mode-coupling approximation for the first order memory kernels, while
equilibrium properties such as site-site static structure factors are deduced
from RISM. The results include the temperature-density(pressure) dependence of
translational diffusion coefficients D and orientational relaxation times t for
acetonitrile in water, methanol in water and methanol in acetonitrile, all in
the limit of infinite dilution. Calculations are performed over the range of
temperatures and densities employing the SPC/E model for water and optimized
site-site potentials for acetonitrile and methanol. The theory is able to
reproduce qualitatively all main features of temperature and density
dependences of D and t observed in real and computer experiments. In
particular, anomalous behavior, i.e. the increase in mobility with density, is
observed for D and t of methanol in water, while acetonitrile in water and
methanol in acetonitrile do not show deviations from the ordinary behavior. The
variety exhibited by the different solute-solvent systems in the density
dependence of the mobility is interpreted in terms of the two competing origins
of friction, which interplay with each other as density increases: the
collisional and dielectric frictions which, respectively, increase and decrease
with increasing density.Comment: 13 pages, 8 eps-figures, 3 tables, RevTeX4-forma
Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy
We report a photoemission study at room temperature on BaFe2X3 (X = S and Se)
and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p
core-level peaks of BaFe2X3 are broad and exhibit two components, indicating
that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe
2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a
charge-transfer satellite. The insulating ground state of CsFe2Se3 can be
viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The
itinerant versus localized behaviors can be associated with the stability of
chalcogen p holes in the two-leg ladder structure.Comment: 5 pages, 5 figures, Accepted in publication for Physical Review
Do Solar Neutrino Experiments Imply New Physics?
None of the 1000 solar models in a full Monte Carlo simulation is consistent
with the results of the chlorine or the Kamiokande experiments. Even if the
solar models are forced artifically to have a \b8 neutrino flux in agreeement
with the Kamiokande experiment, none of the fudged models agrees with the
chlorine observations. The GALLEX and SAGE experiments, which currently have
large statistical uncertainties, differ from the predictions of the standard
solar model by and , respectively.Comment: 7 pages (figures not included), Institute for Advanced Study number
AST 92/51. For a hard copy with the figures, write: [email protected]
Reducing the weak lensing noise for the gravitational wave Hubble diagram using the non-Gaussianity of the magnification distribution
Gravitational wave sources are a promising cosmological standard candle
because their intrinsic luminosities are determined by fundamental physics (and
are insensitive to dust extinction). They are, however, affected by weak
lensing magnification due to the gravitational lensing from structures along
the line of sight. This lensing is a source of uncertainty in the distance
determination, even in the limit of perfect standard candle measurements. It is
commonly believed that the uncertainty in the distance to an ensemble of
gravitational wave sources is limited by the standard deviation of the lensing
magnification distribution divided by the square root of the number of sources.
Here we show that by exploiting the non-Gaussian nature of the lensing
magnification distribution, we can improve this distance determination,
typically by a factor of 2--3; we provide a fitting formula for the effective
distance accuracy as a function of redshift for sources where the lensing noise
dominates.Comment: matches PRD accepted version (expanded description of the
cosmological parameter space + minor changes
The impact of mobile amusement information on use behavior, satisfaction, and loyalty
The relationship between satisfaction and loyalty has been well explored in services marketing or customer relationship management. In this study, the authors studied the relationship of 7 types of service variables under âamusementâ factor. Amusement is one of the three factors extracted from 21 mobile information services. Among many different frameworks of satisfaction-loyalty, we used the framework of âpast use behaviorâ on âsatisfactionâ, and then of âsatisfactionâ on âcontinued use intentionâ (or loyalty), resulting in a strong support of the existing model with positive significant influence on the both paths. Further, our research reveals that, on the both paths, there are stronger, significant positive relationships between a latent variable and the measurement variables for mobile information services with stronger amusement elements than those with other ones. The results lead to useful implications that amusement is a crucial dimension in mobile information services, not only in use motivation, but also on behavior, satisfaction, and continued use intention
The Earth Effect in the MSW Analysis of the Solar Neutrino Experiments
We consider the Earth effect in the MSW analysis of the Homestake,
Kamiokande, GALLEX, and SAGE solar neutrino experiments. Using the
time-averaged data and assuming two-flavor oscillations, the large-angle region
of the combined fit extends to much smaller angles (to ) than when the Earth effect is ignored. However, the additional constraint
from the Kamiokande II day-night data excludes most of the parameter space
sensitive to the Earth effect independent of astrophysical uncertainties, and
leaves only a small large-angle region close to maximal mixing at 90\% C.L. The
nonadiabatic solution remains unaffected by the Earth effect and is still
preferred. Both theoretical and experimental uncertainties are included in the
analysis.Comment: (11 pages, Revtex 3.0 (can be changed to Latex), 3 postscript figures
included, UPR-0570T
Current Status of the Solar Neutrino Problem with Super-Kamiokande
We perform an updated model-independent analysis using the latest solar
neutrino data obtained by Cl and Ga radiochemical experiments,
and most notably by a large water-Cherenkov detector SuperKamiokande with their
504 days of data taking. We confirm that the astrophysical solutions to the
solar neutrino problem are extremely disfavored by the data and a
low-temperature modification of the standard solar model is excluded by more
than 5 . We also propose a new way of illuminating the suppression
pattern of various solar neutrino flux without invoking detailed flavor
conversion mechanisms. It indicates that the strong suppression of Be
neutrinos is no more true when the neutrino flavor conversion is taken into
account.Comment: RevTex file, 10 pages, 7 postscript figure
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