1,463 research outputs found
One- and Two-Nucleon Structure form Green's Function Theory
We review some applications of self-consistent Green's function theory to
studies of one- and two-nucleon structure in finite nuclei.
Large-scale microscopic calculations that employ realistic nuclear forces are
now possible. Effects of long-range correlations are seen to play a dominant
role in determining the quenching of absolute spectroscopic factors. They also
enhance considerably (e,e'pn) cross sections in superparallel kinematics, in
agreement with observations.Comment: Proceedings of the International Symposium on "Forefronts of
Researches in Exotic Nuclear Structures" (Niigata2010)
Modern meson--exchange potential and superfluid neutron star crust matter
In this work we study properties of neutron star crusts, where matter is
expected to consist of nuclei surrounded by superfluid neutrons and a
homogeneous background of relativistic electrons. The nuclei are disposed in a
Coulomb lattice, and it is believed that the structure of the lattice
influences considerably the specific heat of the neutronic matter inside the
crust of a neutron star. Using a modern meson--exchange potential in the
framework of a local--density approximation we calculate the neutronic specific
heat accounting for various shapes of the Coulomb lattice, from spherical to
non--spherical nuclear shapes. We find that a realistic nucleon--nucleon
potential leads to a significant increase in the neutronic specific heat with
respect to that obtained assuming a uniform neutron distribution. The increase
is largest for the non--spherical phase of the crust. These results may have
consequences for the thermal history of young neutron stars.Comment: Revtex, 5 pages, 4 figures included as uuencoded p
Nuclear Theory and Science of the Facility for Rare Isotope Beams
The Facility for Rare Isotope Beams (FRIB) will be a world-leading laboratory
for the study of nuclear structure, reactions and astrophysics. Experiments
with intense beams of rare isotopes produced at FRIB will guide us toward a
comprehensive description of nuclei, elucidate the origin of the elements in
the cosmos, help provide an understanding of matter in neutron stars, and
establish the scientific foundation for innovative applications of nuclear
science to society. FRIB will be essential for gaining access to key regions of
the nuclear chart, where the measured nuclear properties will challenge
established concepts, and highlight shortcomings and needed modifications to
current theory. Conversely, nuclear theory will play a critical role in
providing the intellectual framework for the science at FRIB, and will provide
invaluable guidance to FRIB's experimental programs. This article overviews the
broad scope of the FRIB theory effort, which reaches beyond the traditional
fields of nuclear structure and reactions, and nuclear astrophysics, to explore
exciting interdisciplinary boundaries with other areas.
\keywords{Nuclear Structure and Reactions. Nuclear
Astrophysics. Fundamental Interactions. High Performance
Computing. Rare Isotopes. Radioactive Beams.Comment: 20 pages, 7 figure
Muons and emissivities of neutrinos in neutron star cores
In this work we consider the role of muons in various URCA processes relevant
for neutrino emissions in the core region of neutron stars. The calculations
are done for --stable nuclear matter with and without muons. We find
muons to appear at densities fm, slightly around the
saturation density for nuclear matter fm. The direct URCA
processes for nucleons are forbidden for densities below
fm, however the modified URCA processes with muons ), where is a
nucleon, result in neutrino emissivities comparable to those from
). This
opens up for further possibilities to explain the rapid cooling of neutrons
stars. Superconducting protons reduce however these emissivities at densities
below fm.Comment: 14 pages, Revtex style, 3 uuencoded figs include
Suppression of core polarization in halo nuclei
We present a microscopic study of halo nuclei, starting from the Paris and
Bonn potentials and employing a two-frequency shell model approach. It is found
that the core-polarization effect is dramatically suppressed in such nuclei.
Consequently the effective interaction for halo nucleons is almost entirely
given by the bare G-matrix alone, which presently can be evaluated with a high
degree of accuracy. The experimental pairing energies between the two halo
neutrons in He and Li nuclei are satisfactorily reproduced by our
calculation. It is suggested that the fundamental nucleon-nucleon interaction
can be probed in a clearer and more direct way in halo nuclei than in ordinary
nuclei.Comment: 11 pages, RevTex, 2 postscript figures; major revisions, matches
version to appear in Phys. Rev. Letter
Coupled cluster calculations of ground and excited states of nuclei
The standard and renormalized coupled cluster methods with singles, doubles,
and noniterative triples and their generalizations to excited states, based on
the equation of motion coupled cluster approach, are applied to the He-4 and
O-16 nuclei. A comparison of coupled cluster results with the results of the
exact diagonalization of the Hamiltonian in the same model space shows that the
quantum chemistry inspired coupled cluster approximations provide an excellent
description of ground and excited states of nuclei. The bulk of the correlation
effects is obtained at the coupled cluster singles and doubles level. Triples,
treated noniteratively, provide the virtually exact description
Renormalization of the weak hadronic current in the nuclear medium
The renormalization of the weak charge-changing hadronic current as a
function of the reaction energy release is studied at the nucleonic level. We
have calculated the average quenching factors for each type of current (vector,
axial vector and induced pseudoscalar). The obtained quenching in the axial
vector part is, at zero momentum transfer, 19% for the sd shell and 23% in the
fp shell. We have extended the calculations also to heavier systems such as
Ni and Sn, where we obtain stronger quenchings, 44% and 59%,
respectively. Gamow--Teller type transitions are discussed, along with the
higher order matrix elements. The quenching factors are constant up to roughly
60 MeV momentum transfer. Therefore the use of energy-independent quenching
factors in beta decay is justified. We also found that going beyond the zeroth
and first order operators (in inverse nucleon mass) does not give any
substantial contribution. The extracted renormalization to the ratio
at q=100 MeV is -3.5%, -7.1$%, -28.6%, and +8.7% for mass 16, 40, 56, and 100,
respectively.Comment: 28 pages, 6 figure
VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50
We report the discovery of the gamma-ray burst GRB 000131 and its optical
afterglow. The optical identification was made with the VLT 84 hours after the
burst following a BATSE detection and an Inter Planetary Network localization.
GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal
62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m
follow-up observations. Broad-band and spectroscopic observations of the
spectral energy distribution reveals a sharp break at optical wavelengths which
is interpreted as a Ly-alpha absorption edge at 6700 A. This places GRB 000131
at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in
gamma rays alone was approximately 10^54 erg (depending on the assumed
cosmology). The rapid power-law decay of the afterglow (index alpha=2.25,
similar to bursts with a prior break in the lightcurve), however, indicates
collimated outflow, which relaxes the energy requirements by a factor of < 200.
The afterglow of GRB 000131 is the first to be identified with an 8-m class
telescope.Comment: 8 pages, 7 figures, accepted to A&A Letter
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