41 research outputs found
Relations Between Coefficients of Fractional Parentage
For each of the (9/2), (11/2) and (13/2) single j shells we have only one
state with J=j V=3 for a five particle system. For four identical particles
there can be more than one state of seniority four. We note some ``ratio''
relations for the coefficients of fractional parentage for the four and five
identical particle systems
Weak Interaction Rate Coulomb Corrections in Big Bang Nucleosynthesis
We have applied a fully relativistic Coulomb wave correction to the weak
reactions in the full Kawano/Wagoner Big Bang Nucleosynthesis (BBN) code. We
have also added the zero temperature radiative correction. We find that using
this higher accuracy Coulomb correction results in good agreement with previous
work, giving only a modest 0.04 percent increase in helium mass fraction over
correction prescriptions applied previously in BBN calculations. We have
calculated the effect of these corrections on other light element abundance
yields in BBN and we have studied these yields as functions of electron
neutrino lepton number. This has allowed insights into the role of the Coulomb
correction in the setting of the neutron-to-proton ratio during the BBN epoch.
We find that the lepton capture processes' contributions to this ratio are only
second order in the Coulomb correction.Comment: 8 pages, 3 figure
Investigation of Pygmy Dipole Resonances in the Tin Region
The evolution of the low-energy electromagnetic dipole response with the
neutron excess is investigated along the Sn isotopic chain within an approach
incorporating Hartree-Fock-Bogoljubov (HFB) and multi-phonon
Quasiparticle-Phonon-Model (QPM) theory. General aspects of the relationship of
nuclear skins and dipole sum rules are discussed. Neutron and proton transition
densities serve to identify the Pygmy Dipole Resonance (PDR) as a generic mode
of excitation. The PDR is distinct from the GDR by its own characteristic
pattern given by a mixture of isoscalar and isovector components. Results for
the Sn-Sn isotopes and the several N=82 isotones are presented.
In the heavy Sn-isotopes the PDR excitations are closely related to the
thickness of the neutron skin. Approaching Sn a gradual change from a
neutron to a proton skin is found and the character of the PDR is changed
correspondingly. A delicate balance between Coulomb and strong interaction
effects is found. The fragmentation of the PDR strength in Sn is
investigated by multi-phonon calculations. Recent measurements of the dipole
response in Sn are well reproduced.Comment: 41 pages, 10 figures, PR
Fermion propagators in space-time
The one- and the two-particle propagators for an infinite non-interacting
Fermi system are studied as functions of space-time coordinates. Their
behaviour at the origin and in the asymptotic region is discussed, as is their
scaling in the Fermi momentum. Both propagators are shown to have a divergence
at equal times. The impact of the interaction among the fermions on their
momentum distribution, on their pair correlation function and, hence, on the
Coulomb sum rule is explored using a phenomenological model. Finally the
problem of how the confinement is reflected in the momentum distribution of the
system's constituents is briefly addressed.Comment: 26 pages, 9 figures, accepted for publication on Phys. Rev.
Center-of-mass motion and cross-channel coupling in time-dependent Hartree-Fock theory
We provide a discussion of issues related to the center-of-mass motion and
cross-channel coupling in applications of the time-dependent Hartree-Fock
(TDHF) theory to heavy-ion collisions. We find that the entrance channel
dynamics of a heavy-ion collision as described by TDHF does not seem to be
significantly influenced by these effects, whereas the long-time evolution may
be less reliable.Comment: 4 pages, 4 figure
Quark Masses: An Environmental Impact Statement
We investigate worlds that lie on a slice through the parameter space of the
Standard Model over which quark masses vary. We allow as many as three quarks
to participate in nuclei, while fixing the mass of the electron and the average
mass of the lightest baryon flavor multiplet. We classify as "congenial" worlds
that satisfy the environmental constraint that the quark masses allow for
stable nuclei with charges one, six, and eight, making organic chemistry
possible. Whether a congenial world actually produces observers depends on a
multitude of historical contingencies, beginning with primordial
nucleosynthesis, which we do not explore. Such constraints may be independently
superimposed on our results. Environmental constraints such as the ones we
study may be combined with information about the a priori distribution of quark
masses over the landscape of possible universes to determine whether the
measured values of the quark masses are determined environmentally, but our
analysis is independent of such an anthropic approach.
We estimate baryon masses as functions of quark masses and nuclear masses as
functions of baryon masses. We check for the stability of nuclei against
fission, strong particle emission, and weak nucleon emission. For two light
quarks with charges 2/3 and -1/3, we find a band of congeniality roughly 29 MeV
wide in their mass difference. We also find another, less robust region of
congeniality with one light, charge -1/3 quark, and two heavier, approximately
degenerate charge -1/3 and 2/3 quarks. No other assignment of light quark
charges yields congenial worlds with two baryons participating in nuclei. We
identify and discuss the region in quark-mass space where nuclei would be made
from three or more baryon species.Comment: 40 pages, 16 figures (in color), 4 tables. See paper for a more
detailed abstract. v4: Cleaning up minor typo
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
S-matrix approach to equation of state of nuclear matter
We calculate the equation of state of nuclear matter based on the general
analysis of the grand canonical partition function in the -matrix framework.
In addition to the low mass stable particles and their two-body scattering
channels considered earlier, the calculation includes systematically all the
higher mass particles and their exited states as well as the scattering
channels formed by any number of these species. We estimate the latter
contribution by resonances in all the channels. The resulting model-independent
virial series for pressure gets substantial contribution from the heavy
particles and the channels containing them. The series converges for larger
values of baryon density than found earlier.Comment: Version to appear in PRC, Rapid Communication
Projected multicluster model with Jastrow and linear state dependent correlations for nuclei
Variational wave functions based on a Margenau-Brink cluster model with short
range and state dependent correlations, and angular momentum projection are
obtained for some nuclei with . The calculations have been
carried out starting from the nucleon-nucleon interaction by using the
Variational Monte Carlo method. The configuration used consists of three alpha
clusters located at the apexes of an equilateral triangle, and an additional
cluster, not necessarily of alpha type, forming a tetrahedron. This cluster is
located at the top of its height. Short-range and state dependent correlations
are included by means of a central Jastrow factor and a linear operatorial
correlation factor respectively. Angular momentum projection is performed by
using the Peierls-Yoccoz operators. Optimal structures are obtained for all the
nuclei studied. Some aspects of our methodology have been tested by comparing
with previous calculations carried out without short range correlations. The
binding energy, the root mean square radius, and the one- and two-body
densities are reported. The effects of correlations on both the energy and the
nucleon distribution are analyzed systematically.Comment: 19 pages, 6 figure