3,104 research outputs found
Effects of particle-number conservation on heat capacity of nuclei
By applying the particle-number projection to the finite-temperature BCS
theory, the -shaped heat capacity, which has recently been claimed to be a
fingerprint of the superfluid-to-normal phase transition in nuclei, is
reexamined. It is found that the particle-number (or number-parity) projection
gives -shapes in the heat capacity of nuclei which look qualitatively
similar to the observed ones. These -shapes are accounted for as effects of
the particle-number conservation on the quasiparticle excitations, and occur
even when we keep the superfluidity at all temperatures by assuming a constant
gap in the BCS theory. The present study illustrates significance of the
conservation laws in studying phase transitions of finite systems.Comment: RevTeX4, 12 pages including 5 figures (1 color figure), to be
published in PR
String theory and the KLT-relations between gravity and gauge theory including external matter
We consider the Kawai-Lewellen-Tye (KLT) factorizations of gravity scalar-leg
amplitudes into products of scalar-leg Yang-Mills amplitudes. We check and
examine the factorizations at O(1) in and extend the analysis by
considering KLT-mapping in the case of generic effective Lagrangians for
Yang-Mills theory and gravity.Comment: 7 pages, ReVTeX4, references updated, changes to text and typos
correcte
Neutron Skin Thickness of 90Zr Determined By Charge Exchange Reactions
Charge exchange spin-dipole (SD) excitations of 90Zr are studied by the
90Zr(p,n) and 90Zr(n,p) reactions at 300 MeV. A multipole decomposition
technique is employed to obtain the SD strength distributions in the cross
section spectra. For the first time, a model-independent SD sum rule value is
obtained: 148+/-12 fm^2. The neutron skin thickness of 90Zr is determined to be
0.07+/-0.04 fm from the SD sum rule value.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
Nuclear condensation and symmetry energy of dilute nuclear matter: an S-matrix approach
Based on the general analysis of the grand canonical partition function in
the S-matrix framework, the calculated results on symmetry energy, free energy
and entropy of dilute warm nuclear matter are presented. At a given temperature
and density, the symmetry energy or symmetry free energy of the clusterized
nuclear matter in the S-matrix formulation deviates, particularly at low
temperature and relatively higher density, in a subtle way, from the linear
dependence on the square of the isospin asymmetry parameter
, contrary to those obtained for homogeneous
nucleonic matter. The symmetry coefficients, in the conventional definition,
can then be even negative. The symmetry entropy similarly shows a very
different behavior.Comment: 8 pages, 6 figures. PRC (in press
New Bardeen-Cooper-Schrieffer-type theory at finite temperature with particle-number conservation
We formulate a new Bardeen-Cooper-Schrieffer (BCS)-type theory at finite
temperature, by deriving a set of variational equations of the free energy
after the particle-number projection. With its broad applicability, this theory
can be a useful tool for investigating the pairing phase transition in finite
systems with the particle-number conservation. This theory provides effects of
the symmetry-restoring fluctuation (SRF) for the pairing phenomena in finite
fermionic systems, distinctively from those of additional quantum fluctuations.
It is shown by numerical calculations that the phase transition is compatible
with the conservation in this theory, and that the SRF shifts up the critical
temperature (). This shift of occurs due to
reduction of degrees-of-freedom in canonical ensembles, and decreases only
slowly as the particle-number increases (or as the level spacing narrows), in
contrast to the conventional BCS theory.Comment: 10 pages including 3 figures, to be published in Phys. Rev.
Nuclear phenomena derived from quark-gluon strings
We propose a QCD based many-body model for the nucleus where the strong
coupling regime is controlled by a three body string force and the weak
coupling regime is dominated by a pairing force. This model operates
effectively with a quark-gluon Lagrangian containing a pairing force from
instantons and a baryonic string term which contains a confining potential. The
unified model for weak and strong coupling regimes, is, however, only
consistent at the border of perturbative QCD. The baryonic string force is
necessary, as a {stability and} compressibility analysis shows, for the
occurrence of the phases of nuclear matter. The model exhibits a quark
deconfinement transition and chiral restoration which are suggested by QCD and
give qualitatively correct numerics. The effective model is shown to be
isomorphic to the Nambu-Jona-Lasinio model and exhibits the correct chirality
provided that the chiral fields are identified with the 2-particle strings,
which are natural in a QCD frameworkComment: 17 pages, 4 figures, 2 table
Quadrupole collective variables in the natural Cartan-Weyl basis
The matrix elements of the quadrupole collective variables, emerging from
collective nuclear models, are calculated in the natural Cartan-Weyl basis of
O(5) which is a subgroup of a covering structure. Making
use of an intermediate set method, explicit expressions of the matrix elements
are obtained in a pure algebraic way, fixing the -rotational structure
of collective quadrupole models.Comment: submitted to Journal of Physics
Three-body model calculations for 16C nucleus
We apply a three-body model consisting of two valence neutrons and the core
nucleus C in order to investigate the ground state properties and the
electronic quadrupole transition of the C nucleus. The discretized
continuum spectrum within a large box is taken into account by using a
single-particle basis obtained from a Woods-Saxon potential. The calculated
B(E2) value from the first 2 state to the ground state shows good agreement
with the observed data with the core polarization charge which reproduces the
experimental B(E2) value for C. We also show that the present
calculation well accounts for the longitudinal momentum distribution of
C fragment from the breakup of C nucleus. We point out that the
dominant ( configuration in the ground state of C plays a
crucial role for these agreement.Comment: 5 pages, 3 figures, 3 table
Consequences of self-consistency violations in Hartree-Fock random-phase approximation calculations of the nuclear breathing mode energy
We provide for the first time accurate assessments of the consequences of
violations of self-consistency in the Hartree-Fock based random phase
approximation (RPA) as commonly used to calculate the energy of the
nuclear breathing mode. Using several Skyrme interactions we find that the
self-consistency violated by ignoring the spin-orbit interaction in the RPA
calculation causes a spurious enhancement of the breathing mode energy for spin
unsaturated systems. Contrarily, neglecting the Coulomb interaction in the RPA
or performing the RPA calculations in the TJ scheme underestimates the
breathing mode energy. Surprisingly, our results for the Zr and
Pb nuclei for several Skyrme type effective nucleon-nucleon
interactions having a wide range of nuclear matter incompressibility ( MeV) and symmetry energy ( MeV) indicate that
the net uncertainty ( MeV) is comparable to the
experimental one.Comment: Revtex file (11 pages), Accepted for the publication in Phys. Rev.
- âŠ