6,097 research outputs found
Weak proton capture on 3He
The astrophysical S-factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to realistic Hamiltonians consisting of the Argonne v14 or
Argonne v18 two-nucleon and Urbana-VIII or Urbana-IX three-nucleon
interactions. The nuclear weak charge and current operators have vector and
axial-vector components, that include one- and many-body terms. All possible
multipole transitions connecting any of the p 3He S- and P-wave channels to the
4He bound state are considered. The S-factor at a p 3He center-of-mass energy
of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 10^{-20} keV
b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value
adopted in the standard solar model. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor. The energy
dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 10^{-20}
keV b, only 5 % smaller than the 10 keV result quoted above. The model
dependence is also found to be weak: the zero-energy S-factor is calculated to
be 10.2 10^{-20} keV b with the older AV14/UVIII model, only 6 % larger than
the AV18/UIX result. Our best estimate for the S-factor at 10 keV is therefore
(10.1 \pm 0.6) 10^{-20} keV b, when the theoretical uncertainty due to the
model dependence is included. This value for the calculated S-factor is not as
large as determined in fits to the Super-Kamiokande data in which the hep flux
normalization is free. However, the precise calculation of the S-factor and the
consequent absolute prediction for the hep neutrino flux will allow much
greater discrimination among proposed solar neutrino oscillation solutions.Comment: 54 pages RevTex file, 6 PostScript figures, submitted to Phys. Rev.
The Three-Nucleon System Near the N-d Threshold
The three-nucleon system is studied at energies a few hundred keV above the
N-d threshold. Measurements of the tensor analyzing powers and
for p-d elastic scattering at keV are presented
together with the corresponding theoretical predictions. The calculations are
extended to very low energies since they are useful for extracting the p-d
scattering lengths from the experimental data. The interaction considered here
is the Argonne V18 potential plus the Urbana three-nucleon potential. The
calculation of the asymptotic D- to S-state ratio for H and He, for
which recent experimental results are available, is also presented.Comment: Latex, 11 pages, 2 figures, to be published in Phy.Lett.
Benchmark calculation for proton-deuteron elastic scattering observables including Coulomb
Two independent calculations of proton-deuteron elastic scattering
observables including Coulomb repulsion between the two protons are compared in
the proton lab energy region between 3 MeV and 65 MeV. The hadron dynamics is
based on the purely nucleonic charge-dependent AV18 potential. Calculations are
done both in coordinate space and momentum space. The coordinate-space
calculations are based on a variational solution of the three-body
Schr\"odinger equation using a correlated hyperspherical expansion for the wave
function. The momentum-space calculations proceed via the solution of the
Alt-Grassberger-Sandhas equation using the screened Coulomb potential and the
renormalization approach. Both methods agree within 1% on all observables,
showing the reliability of both numerical techniques in that energy domain. At
energies below three-body breakup threshold the coordinate-space method remains
favored whereas at energies higher than 65 MeV the momentum-space approach
seems to be more efficient.Comment: Submitted to Phys. Rev.
XMMU J100750.5+125818: A strong lensing cluster at z=1.082
We report on the discovery of the X-ray luminous cluster XMMU
J100750.5+125818 at redshift 1.082 based on 19 spectroscopic members, which
displays several strong lensing features. SED modeling of the lensed arc
features from multicolor imaging with the VLT and the LBT reveals likely
redshifts ~2.7 for the most prominent of the lensed background galaxies. Mass
estimates are derived for different radii from the velocity dispersion of the
cluster members, M_200 ~ 1.8 10^{14} Msun, from the X-ray spectral parameters,
M_500 ~ 1.0 10^{14} Msun, and the largest lensing arc, M_SL ~ 2.3 10^{13} Msun.
The projected spatial distribution of cluster galaxies appears to be elongated,
and the brightest galaxy lies off center with respect to the X-ray emission
indicating a not yet relaxed structure. XMMU J100750.5+125818 offers excellent
diagnostics of the inner mass distribution of a distant cluster with a
combination of strong and weak lensing, optical and X-ray spectroscopy.Comment: A&A, accepted for publicatio
Hubble Space Telescope Imaging in the Chandra Deep Field South: III. Quantitative Morphology of the 1Ms Chandra Counterparts and Comparison with the Field Population
We present quantitative morphological analyses of 37 HST/WFPC2 counterparts
of X-ray sources in the 1 Ms Chandra Deep Field-South (CDFS). We investigate:
1) 1-D surface brightness profiles via isophotal ellipse fitting; 2) 2-D, PSF-
convolved, bulge+disk+nucleus profile-fitting; 3) asymmetry and concentration
indices compared with all ~3000 sources in our three WFPC2 fields; and 4) near-
neighbor analyses comparing local environments of X-ray sources versus the
field control sample. Significant nuclear point-source optical components
appear in roughly half of the resolved HST/WFPC2 counterparts, showing a narrow
range of F_X/F_{opt,nuc} consistent with the several HST-unresolved X-ray
sources (putative type-1 AGN) in our fields. We infer roughly half of the
HST/WFPC2 counterparts host unobscured AGN, which suggests no steep decline in
the type-1/type-2 ratio out to the redshifts z~0.5-1 typical of our sources.
The concentration indices of the CDFS counterparts are clearly larger on
average than those of the field distribution, at 5-sigma, suggesting that the
strong correlation between central black hole mass and host galaxy properties
(including concentration index) observed in nearby galaxies is already evident
by z~0.5-1. By contrast, the asymmetry index distribution of the 21 resolved
CDFS sources at I<23 is indistinguishable from the I<23 field. Moreover, the
frequency of I<23 near neighbors around the CDFS counterparts is not
significantly different from the field sample. These results, combined with
previous similar findings for local samples, suggest that recent merger/
interaction history is not a good indicator of AGN activity over a substantial
range of look-back time.Comment: 30 pages, incl. 8 figures; accepted for publication in the
Astrophysical Journa
The Evolutionary Status of Clusters of Galaxies at z ~ 1
Combined HST, X-ray, and ground-based optical studies show that clusters of
galaxies are largely "in place" by , an epoch when the Universe was
less than half its present age. High resolution images show that elliptical,
S0, and spiral galaxies are present in clusters at redshifts up to . Analysis of the CMDs suggest that the cluster ellipticals formed their
stars several Gyr earlier, near redshift 3. The morphology--density relation is
well established at , with star-forming spirals and irregulars residing
mostly in the outer parts of the clusters and E/S0s concentrated in dense
clumps. The intracluster medium has already reached the metallicity of
present-day clusters. The distributions of the hot gas and early-type galaxies
are similar in clusters, indicating both have largely virialized in
the deepest potentials wells. In spite of the many similarities between
and present-day clusters, there are significant differences. The
morphologies revealed by the hot gas, and particularly the early-type galaxies,
are elongated rather than spherical. We appear to be observing the clusters at
an epoch when the sub-clusters and groups are still assembling into a single
regular cluster. Support for this picture comes from CL0152 where the gas
appears to be lagging behind the luminous and dark mass in two merging
sub-components. Moreover, the luminosity difference between the first and
second brightest cluster galaxies at is smaller than in 93% of
present-day Abell clusters, which suggests that considerable luminosity
evolution through merging has occurred since that epoch. Evolution is also seen
in the bolometric X-ray luminosity function.Comment: 18 pages, 12 figures, to appear in Penetrating Bars through Masks of
Cosmic Dust: the Hubble Tuing Fork Strikes a New Note, eds. D.L. Block, K.C.
Freeman, I. Puerari & R. Groess. Figures degraded to meet astroph size limit;
a version with higher resolution figures may be downloaded from:
http://acs.pha.jhu.edu/~jpb/z1clusters/ford_clusters.pd
Calculation of the Alpha--Particle Ground State within the Hyperspherical Harmonic Basis
The problem of calculating the four--nucleon bound state properties for the
case of realistic two- and three-body nuclear potentials is studied using the
hyperspherical harmonic (HH) approach. A careful analysis of the convergence of
different classes of HH functions has been performed. A restricted basis is
chosen to allow for accurate estimates of the binding energy and other
properties of the 4He ground state. Results for various modern two-nucleon and
two- plus three-nucleon interactions are presented. The 4He asymptotic
normalization constants for separation in 2+2 and 1+3 clusters are also
computed.Comment: 29 pages, 4 figures, 11 tables, revtex
Low energy n-\nuc{3}{H} scattering : a novel testground for nuclear interaction
The low energy n-\nuc{3}{H} elastic cross sections near the resonance peak
are calculated by solving the 4-nucleon problem with realistic NN interactions.
Three different methods -- Alt, Grassberger and Shandas (AGS), Hyperspherical
Harmonics and Faddeev-Yakubovsky -- have been used and their respective results
are compared. We conclude on a failure of the existing NN forces to reproduce
the n-\nuc{3}{H} total cross section.Comment: To be published in Phys. Rev.
Evidence for Three Nucleon Force Effects in p-d Elastic Scattering
A new measurement of the p-d differential cross section at Ep= 1 MeV has been
performed. These new data and older data sets at energies below the deuteron
breakup are compared to calculations using the two-nucleon Argonne v18 and the
three-nucleon Urbana IX potentials. A quantitative estimate of the capability
of these interactions to describe the data is given in terms of a chi^2
analysis. The chi^2 per datum drastically improves when the three-nucleon
interaction is included in the Hamiltonian.Comment: 13 pages, 5 figures, to be published in Phys. Rev.
Ferromagnetic transition of a two-component Fermi gas of Hard Spheres
We use microscopic many-body theory to analyze the problem of itinerant
ferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple
arguments, we show that the available theoretical predictions for the onset of
the ferromagnetic transition predict a transition point at a density () that is too large to be compatible with the universal low-density
expansion of the energy. We present new variational calculations for the
hard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that
shift the transition to higher densities (). Backflow
correlations, which are mainly active in the unpolarized system, are essential
for this shift
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