786 research outputs found
Low-momentum interactions with Brown-Rho-Ericson scalings and the density dependence of the nuclear symmetry energy
We have calculated the nuclear symmetry energy up to
densities of with the effects from the Brown-Rho (BR) and
Ericson scalings for the in-medium mesons included. Using the
low-momentum interaction with and without such scalings, the equations of state
(EOS) of symmetric and asymmetric nuclear matter have been calculated using a
ring-diagarm formalism where the particle-particle-hole-hole ring diagrams are
included to all orders. The EOS for symmetric nuclear matter and neutron matter
obtained with linear BR scaling are both overly stiff compared with the
empirical constraints of Danielewicz {\it et al.} \cite{daniel02}. In contrast,
satisfactory results are obtained by either using the nonlinear Ericson scaling
or by adding a Skyrme-type three-nucleon force (TNF) to the unscaled
interaction.
Our results for obtained with the nonlinear Ericson scaling
are in good agreement with the empirical values of Tsang {\it et al.}
\cite{tsang09} and Li {\it et al.} \cite{li05}, while those with TNF are
slightly below these values. For densities below the nuclear saturation density
, the results of the above calculations are nearly equivalent to each
other and all in satisfactory agreement with the empirical values.Comment: 7 pages, 6 figure
Shell model description of the 14C dating beta decay with Brown-Rho-scaled NN interactions
We present shell model calculations for the beta-decay of the 14C ground
state to the 14N ground state, treating the states of the A=14 multiplet as two
0p holes in an 16O core. We employ low-momentum nucleon-nucleon (NN)
interactions derived from the realistic Bonn-B potential and find that the
Gamow-Teller matrix element is too large to describe the known lifetime. By
using a modified version of this potential that incorporates the effects of
Brown-Rho scaling medium modifications, we find that the GT matrix element
vanishes for a nuclear density around 85% that of nuclear matter. We find that
the splitting between the (J,T)=(1+,0) and (J,T)=(0+,1) states in 14N is
improved using the medium-modified Bonn-B potential and that the transition
strengths from excited states of 14C to the 14N ground state are compatible
with recent experiments.Comment: 4 pages, 5 figures Updated to include referee comments/suggestion
Unitarity potentials and neutron matter at the unitary limit
We study the equation of state of neutron matter using a family of unitarity
potentials all of which are constructed to have infinite scattering
lengths . For such system, a quantity of much interest is the ratio
where is the true ground-state energy of the system,
and is that for the non-interacting system. In the limit of
, often referred to as the unitary limit, this ratio is
expected to approach a universal constant, namely . In the
present work we calculate this ratio using a family of hard-core
square-well potentials whose can be exactly obtained, thus enabling us to
have many potentials of different ranges and strengths, all with infinite
. We have also calculated using a unitarity CDBonn potential
obtained by slightly scaling its meson parameters. The ratios given by
these different unitarity potentials are all close to each other and also
remarkably close to 0.44, suggesting that the above ratio is indifferent
to the details of the underlying interactions as long as they have infinite
scattering length. A sum-rule and scaling constraint for the renormalized
low-momentum interaction in neutron matter at the unitary limit is discussed.Comment: 7.5 pages, 7 figure
Neutron star, -stable ring-diagram equation of state and Brown-Rho scaling
Neutron star properties, such as its mass, radius, and moment of inertia, are
calculated by solving the Tolman-Oppenheimer-Volkov (TOV) equations using the
ring-diagram equation of state (EOS) obtained from realistic low-momentum NN
interactions . Several NN potentials (CDBonn, Nijmegen, Argonne V18
and BonnA) have been employed to calculate the ring-diagram EOS where the
particle-particle hole-hole ring diagrams are summed to all orders. The proton
fractions for different radial regions of a -stable neutron star are
determined from the chemical potential conditions . The neutron star masses, radii and moments of inertia given by the
above potentials all tend to be too small compared with the accepted values.
Our results are largely improved with the inclusion of medium corrections based
on Brown-Rho scaling where the in-medium meson masses, particularly those of
, and , are slightly decreased compared with their
in-vacuum values. Representative results using such medium corrected
interactions are neutron star mass , radius km
and moment of inertia . The mass-radius trajectories
given by the above four realistic NN potentials are by and large overlapping.Comment: 12.7 pages, 13 figures, 3 table
Half-Skyrmions and the Equation of State for Compact-Star Matter
The half-skyrmions that appear in dense baryonic matter when skyrmions are
put on crystals modify drastically hadron properties in dense medium and affect
strongly the nuclear tensor forces, thereby influencing the equation of state
(EoS) of dense nuclear and asymmetric nuclear matter. The matter comprised of
half skyrmions has vanishing quark condensate but non-vanishing pion decay
constant and could be interpreted as a hadronic dual of strong-coupled quark
matter. We infer from this observation combined with certain predictions of
hidden local symmetry in low-energy hadronic interactionsa a set of new scaling
laws -- called "new-BR" -- for the parameters in nuclear effective field theory
controlled by renormalization-group flow. They are subjected to the EoS of
symmetric and asymmetric nuclear matter, and are then applied to nuclear
symmetry energies and properties of compact stars. The changeover from the
skyrmion matter to a half-skyrmion matter that takes place after the cross-over
density provides a simple and natural field theoretic explanation for
the change of the EoS from soft to stiff at a density above that of nuclear
matter required for compact stars as massive as . Cross-over
density in the range 1.5n_0 \lsim n_{1/2} \lsim 2.0 n_0 has been employed,
and the possible skyrmion half-skyrmion coexistence {or cross-over} near
is discussed. The novel structure of {the tensor forces and} the EoS
obtained with the new-BR scaling is relevant for neutron-rich nuclei and
compact star matter and could be studied in RIB (rare isotope beam) machines.Comment: 12 pages, 7 figures, slightly revised for PRC, in pres
The relativistic self-energy in nuclear dynamics
It is a well known fact that Dirac phenomenology of nuclear forces predicts
the existence of large scalar and vector mean fields in matter. To analyse the
relativistic self-energy in a model independent way, modern high precision
nucleon-nucleon () potentials are mapped on a relativistic operator basis
using projection techniques. This allows to compare the various potentials at
the level of covariant amplitudes were a remarkable agreement is found. It
allows further to calculate the relativistic self-energy in nuclear matter in
Hartree-Fock approximation. Independent of the choice of the nucleon-nucleon
interaction large scalar and vector mean fields of several hundred MeV
magnitude are generated at tree level. In the framework of chiral EFT these
fields are dominantly generated by contact terms which occur at next-to-leading
order in the chiral expansion. Consistent with Dirac phenomenology the
corresponding low energy constants which generate the large fields are closely
connected to the spin-orbit interaction in scattering. The connection to
QCD sum rules is discussed as well.Comment: 49 pages, 13 figure
Influence of a Z+(1540) resonance on K+N scattering
The impact of a (I=0, J^P=1/2^+) Z^+(1540) resonance with a width of 5 MeV or
more on the K+N (I=0) elastic cross section and on the P01 phase shift is
examined within the KN meson-exchange model of the Juelich group. It is shown
that the rather strong enhancement of the cross section caused by the presence
of a Z^+ with the above properties is not compatible with the existing
empirical information on KN scattering. Only a much narrower Z^+ state could be
reconciled with the existing data -- or, alternatively, the Z^+ state must lie
at an energy much closer to the KN threshold.Comment: 9 pages, RevTeX, 3 eps figure
Nucleon Resonances with Hidden Charm in Coupled-Channel Models
The model dependence of the predictions of nucleon resonances with hidden
charm is investigated. We consider several coupled-channel models which are
derived from relativistic quantum field theory by using (1) a unitary
transformation method, and (2) the three-dimensional reductions of
Bethe-Salpeter Equation. With the same vector meson exchange mechanism, we find
that all models give very narrow molecular-like nucleon resonances with hidden
charm in the mass range of 4.3 GeV 4.5 GeV, in consistent with the
previous predictions.Comment: 17 pages, 3 figure
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