533 research outputs found
Updated opacities from the opacity project
Using the code autostructure, extensive calculations of inner-shell atomic data have been made for the chemical elements He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, Mn, Fe and Ni. The results are used to obtain updated opacities from the Opacity Project (OP). A number of other improvements on earlier work have also been included. Rosseland-mean opacities from the OP are compared with those from OPAL. Differences of 5-10 per cent occur. The OP gives the 'Z-bump', at log(T) 5.2, to be shifted to slightly higher temperatures. The opacities from the OP, as functions of temperature and density, are smoother than those from OPAL. The accuracy of the integrations used to obtain mean opacities can depend on the frequency mesh used. Tests involving variation of the numbers of frequency points show that for typical chemical mixtures the OP integrations are numerically correct to within 0.1 per cent. The accuracy of the interpolations used to obtain mean opacities for any required values of temperature and density depends on the temperature-density meshes used. Extensive tests show that, for all cases of practical interest, the OP interpolations give results correct to better than 1 per cent. Prior to a number of recent investigations which have indicated a need for downward revisions in the solar abundances of oxygen and other elements, there was good agreement between properties of the Sun deduced from helioseismology and from stellar evolution models calculated using OPAL opacities. The revisions destroy that agreement. In a recent paper, Bahcall et al. argue that the agreement would be restored if opacities for the regions of the Sun with 2 × 106T 5 × 106 K (0.7-0.4 R) were larger than those given by OPAL by about 10 per cent. In the region concerned, the present results from the OP do not differ from those of OPAL by more than 2.5 per cent
Observational Constraints on Cosmological Models with the Updated Long Gamma-Ray Bursts
In the present work, by the help of the newly released Union2 compilation
which consists of 557 Type Ia supernovae (SNIa), we calibrate 109 long
Gamma-Ray Bursts (GRBs) with the well-known Amati relation, using the
cosmology-independent calibration method proposed by Liang {\it et al.}. We
have obtained 59 calibrated high-redshift GRBs which can be used to constrain
cosmological models without the circularity problem (we call them ``Hymnium''
GRBs sample for convenience). Then, we consider the joint constraints on 7
cosmological models from the latest observational data, namely, the combination
of 557 Union2 SNIa dataset, 59 calibrated Hymnium GRBs dataset (obtained in
this work), the shift parameter from the WMAP 7-year data, and the distance
parameter of the measurement of the baryon acoustic oscillation (BAO) peak
in the distribution of SDSS luminous red galaxies. We also briefly consider the
comparison of these 7 cosmological models.Comment: 19 pages, 3 tables, 10 figures, revtex4; v2: accepted for publication
in JCAP; v3: published versio
Cosmological Constraints from calibrated Yonetoku and Amati relation implies Fundamental plane of Gamma-ray bursts
We consider two empirical relations using data only from the prompt emission
of Gamma-Ray Bursts (GRBs), peak energy () - peak luminosity ()
relation (so called Yonetoku relation) and -isotropic energy () relation (so called Amati relation). We first suggest the independence
of the two relations although they have been considered similar and dependent.
From this viewpoint, we compare constraints on cosmological parameters,
and , from the Yonetoku and Amati relations
calibrated by low-redshift GRBs with . We found that they are
different in 1- level, although they are still consistent in 2-
level. This and the fact that both Amati and Yonetoku relations have systematic
errors larger than statistical errors suggest the existence of a hidden
parameter of GRBs. We introduce the luminosity time defined by as a hidden parameter to obtain a generalized Yonetoku
relation as . The new relation has much smaller systematic
error, 30%, and can be regarded as "Fundamental plane" of GRBs. We show a
possible radiation model for this new relation. Finally we apply the new
relation for high-redshift GRBs with to obtain
, which is consistent with the
concordance cosmological model within 2- level.Comment: 5 pages, 6 figures, published in JCA
Probing bulk viscous matter-dominated models with Gamma-ray bursts
In this paper we extend the range of consistency of a constant bulk viscosity
model to redshifts up to . In this model the dark sector of the
cosmic substratum is a viscous fluid with pressure , where
is the fluid-expansion scalar and is the coefficient of bulk
viscosity. Using the sample of 59 high-redshift GRBs reported by Wei (2010), we
calibrate GRBs at low redshifts with the Union 2 sample of SNe Ia, avoiding
then the circularity problem. Testing the constant bulk viscosity model with
GRBs we found the best fit for the viscosity parameter in the
range , being so consistent with previous probes; we also
determined the deceleration parameter and the redshift of transition to
accelerated expansion. Besides we present an updated analysis of the model with
CMB5-year data and CMB7-year data, as well as with the baryon acoustic peak
BAO. From the statistics with CMB it turns out that the model does not describe
in a feasible way the far far epoch of recombination of the universe, but is in
very good concordance for epochs as far as till present.Comment: 11 pages, 3 figures, submitted to JCA
Effective theory of the Delta(1232) in Compton scattering off the nucleon
We formulate a new power-counting scheme for a chiral effective field theory
of nucleons, pions, and Deltas. This extends chiral perturbation theory into
the Delta-resonance region. We calculate nucleon Compton scattering up to
next-to-leading order in this theory. The resultant description of existing
p cross section data is very good for photon energies up to about 300
MeV. We also find reasonable numbers for the spin-independent polarizabilities
and .Comment: 29 pp, 9 figs. Minor revisions. To be published in PR
Resonances of low orders in the planetary system of HD37124
The full set of published radial velocity data (52 measurements from Keck +
58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed.
Two families of dynamically stable high-eccentricity orbital solutions for the
planetary system are found. In the first one, the outer planets c and d are
trapped in the 2/1 mean-motion resonance. The second family of solutions
corresponds to the 5/2 mean-motion resonance between these planets. In both
families, the planets are locked in (or close to) an apsidal corotation
resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation
(with the difference between the longitudes of periastra ), whereas in the case of the 5/2 MMR it is a symmetric antialigned
one ().
It remains also possible that the two outer planets are not trapped in an
orbital resonance. Then their orbital eccentricities should be relatively small
(less than, say, 0.15) and the ratio of their orbital periods is unlikely to
exceed .Comment: 28 pages, 10 figures, 3 tables; Accepted to Celestial Mechanics and
Dynamical Astronom
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar
-> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were
collected with the DO detector from an integrated luminosity of 162 pb^{-1}
delivered by the Fermilab Tevatron Collider. The cross section times branching
fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV
and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum)
pb. The one-dimensional 95% confidence level limits on anomalous couplings are
-0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
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