807 research outputs found
The nonrelativistic limit of the relativistic point coupling model
We relate the relativistic finite range mean-field model (RMF-FR) to the
point-coupling variant and compare the nonlinear density dependence. From this,
the effective Hamiltonian of the nonlinear point-coupling model in the
nonrelativistic limit is derived. Different from the nonrelativistic models,
the nonlinearity in the relativistic models automatically yields contributions
in the form of a weak density dependence not only in the central potential but
also in the spin-orbit potential. The central potential affects the bulk and
surface properties while the spin-orbit potential is crucial for the shell
structure of finite nuclei. A modification in the Skyrme-Hartree-Fock model
with a density-dependent spin-orbit potential inspired by the point-coupling
model is suggested.Comment: 21 pages, latex, 1 eps figure. accepted for publication in annals of
physic
Four-Quark Condensates in Nucleon QCD Sum Rules
The in-medium behavior of the nucleon spectral density including
self-energies is revisited within the framework of QCD sum rules. Special
emphasis is given to the density dependence of four-quark condensates. A
complete catalog of four-quark condensates is presented and relations among
them are derived. Generic differences of such four-quark condensates occurring
in QCD sum rules for light baryons and light vector mesons are discussed.Comment: Version accepted for publication: corrected typos, minor changes
based on referee comments included, reference adde
The Axial-Vector Current in Nuclear Many-Body Physics
Weak-interaction currents are studied in a recently proposed effective field
theory of the nuclear many-body problem. The Lorentz-invariant effective field
theory contains nucleons, pions, isoscalar scalar () and vector
() fields, and isovector vector () fields. The theory exhibits a
nonlinear realization of chiral symmetry and has three
desirable features: it uses the same degrees of freedom to describe the
axial-vector current and the strong-interaction dynamics, it satisfies the
symmetries of the underlying theory of quantum chromodynamics, and its
parameters can be calibrated using strong-interaction phenomena, like hadron
scattering or the empirical properties of finite nuclei. Moreover, it has
recently been verified that for normal nuclear systems, it is possible to
systematically expand the effective lagrangian in powers of the meson fields
(and their derivatives) and to reliably truncate the expansion after the first
few orders. Here it is shown that the expressions for the axial-vector current,
evaluated through the first few orders in the field expansion, satisfy both
PCAC and the Goldberger--Treiman relation, and it is verified that the
corresponding vector and axial-vector charges satisfy the familiar chiral
charge algebra. Explicit results are derived for the Lorentz-covariant,
axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange
currents can be deduced.Comment: 32 pages, REVTeX 4.0 with 12pt.rtx, aps.rtx, revsymb.sty,
revtex4.cls, plus 14 figures; two sentences added in Summary; two references
adde
Nuclear Ground State Observables and QCD Scaling in a Refined Relativistic Point Coupling Model
We present results obtained in the calculation of nuclear ground state
properties in relativistic Hartree approximation using a Lagrangian whose
QCD-scaled coupling constants are all natural (dimensionless and of order 1).
Our model consists of four-, six-, and eight-fermion point couplings (contact
interactions) together with derivative terms representing, respectively, two-,
three-, and four-body forces and the finite ranges of the corresponding mesonic
interactions. The coupling constants have been determined in a self-consistent
procedure that solves the model equations for representative nuclei
simultaneously in a generalized nonlinear least-squares adjustment algorithm.
The extracted coupling constants allow us to predict ground state properties of
a much larger set of even-even nuclei to good accuracy. The fact that the
extracted coupling constants are all natural leads to the conclusion that QCD
scaling and chiral symmetry apply to finite nuclei.Comment: 44 pages, 13 figures, 9 tables, REVTEX, accepted for publication in
Phys. Rev.
Sensitivities of the Proton-Nucleus Elastical Scattering Observables of 6He and 8He at Intermediate Energies
We investigate the use of proton-nucleus elastic scattering experiments using
secondary beams of 6He and 8He to determine the physical structure of these
nuclei. The sensitivity of these experiments to nuclear structure is examined
by using four different nuclear structure models with different spatial
features using a full-folding optical potential model. The results show that
elastic scattering at intermediate energies (<100 MeV per nucleon) is not a
good constraint to be used to determine features of structure. Therefore
researchers should look elsewhere to put constraints on the ground state wave
function of the 6He and 8He nuclei.Comment: To be published in Phys. Rev.
Reflecting on Hybrid Events: Learning from a Year of Hybrid Experiences
The COVID-19 pandemic led to a sudden shift to virtual work and events, with the last two years enabling an appropriated and rather simulated togetherness - the hybrid mode. As we return to in-person events, it is important to reflect on not only what we learned about technologies and social justice, but about the types of events we desire, and how to re-design them accordingly. This SIG aims to reflect on hybrid events and their execution: scaling them across sectors, communities, and industries; considering trade-offs when choosing technologies; studying best practices and defining measures of "success"for hybrid events; and finally, identifying and charting the wider social, ethical, and legal implications of hybrid formats. This SIG will consolidate these topics by inviting participants to collaboratively reflect on previous hybrid experiences and what can be learned from them
Pairing Properties In Relativistic Mean Field Models Obtained From Effective Field Theory
We apply recently developed effective field theory nuclear models in mean
field approximation (parameter sets G1 and G2) to describe ground-state
properties of nuclei from the valley of -stability up to the drip lines.
For faster calculations of open-shell nuclei we employ a modified BCS approach
which takes into account quasi-bound levels owing to their centrifugal barrier,
with a constant pairing strength. We test this simple prescription by comparing
with available Hartree-plus-Bogoliubov results. Using the new effective
parameter sets we then compute separation energies, density distributions and
spin--orbit potentials in isotopic (isotonic) chains of nuclei with magic
neutron (proton) numbers. The new forces describe the experimental systematics
similarly to conventional non-linear relativistic force
parameters like NL3.Comment: 29 pages, 17 figures, accepted for publication in PR
Relativistic Nuclear Energy Density Functionals: Mean-Field and Beyond
Relativistic energy density functionals (EDF) have become a standard tool for
nuclear structure calculations, providing a complete and accurate, global
description of nuclear ground states and collective excitations. Guided by the
medium dependence of the microscopic nucleon self-energies in nuclear matter,
semi-empirical functionals have been adjusted to the nuclear matter equation of
state and to bulk properties of finite nuclei, and applied to studies of
arbitrarily heavy nuclei, exotic nuclei far from stability, and even systems at
the nucleon drip-lines. REDF-based structure models have also been developed
that go beyond the static mean-field approximation, and include collective
correlations related to the restoration of broken symmetries and to
fluctuations of collective variables. These models are employed in analyses of
structure phenomena related to shell evolution, including detailed predictions
of excitation spectra and electromagnetic transition rates.Comment: To be published in Progress in Particle and Nuclear Physic
QCD Sum Rules and Applications to Nuclear Physics
Applications of QCD sum-rule methods to the physics of nuclei are reviewed,
with an emphasis on calculations of baryon self-energies in infinite nuclear
matter. The sum-rule approach relates spectral properties of hadrons
propagating in the finite-density medium, such as optical potentials for
quasinucleons, to matrix elements of QCD composite operators (condensates). The
vacuum formalism for QCD sum rules is generalized to finite density, and the
strategy and implementation of the approach is discussed. Predictions for
baryon self-energies are compared to those suggested by relativistic nuclear
physics phenomenology. Sum rules for vector mesons in dense nuclear matter are
also considered.Comment: 92 pages, ReVTeX, 9 figures can be obtained upon request (to Xuemin
Jin
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