10,972 research outputs found
Delineating effects of tensor force on the density dependence of nuclear symmetry energy
In this talk, we report results of our recent studies to delineate effects of
the tensor force on the density dependence of nuclear symmetry energy within
phenomenological models. The tensor force active in the isosinglet
neutron-proton interaction channel leads to appreciable depletion/population of
nucleons below/above the Fermi surface in the single-nucleon momentum
distribution in cold symmetric nuclear matter (SNM). We found that as a
consequence of the high momentum tail in SNM the kinetic part of the symmetry
energy is significantly below the well-known Fermi gas
model prediction of approximately . With about 15%
nucleons in the high momentum tail as indicated by the recent experiments at
J-Lab by the CLAS Collaboration, the is negligibly small.
It even becomes negative when more nucleons are in the high momentum tail in
SNM. These features have recently been confirmed by three independent studies
based on the state-of-the-art microscopic nuclear many-body theories. In
addition, we also estimate the second-order tensor force contribution to the
potential part of the symmetry energy. Implications of these findings in
extracting information about nuclear symmetry energy from nuclear reactions are
discussed briefly.Comment: Talk given by Chang Xu at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Chiral anomaly and anomalous finite-size conductivity in graphene
Graphene is a monolayer of carbon atoms packed into a hexagon lattice to host
two pairs of massless two-dimensional Dirac fermions in the absence of or with
negligible spin-orbit coupling. It is known that the existence of non-zero
electric polarization in reduced momentum space which is associated with a
hidden chiral symmetry will lead to the zero-energy flat band of zigzag
nanoribbon. The Adler-Bell-Jackiw chiral anomaly or non-conservation of chiral
charges at different valleys can be realized in a confined ribbon of finite
width. In the laterally diffusive regime, the finite-size correction to
conductivity is always positive and goes inversely with the square of the
lateral dimension W, which is different from the finite-size correction
inversely with W from boundary modes. This anomalous finite-size conductivity
reveals the signature of the chiral anomaly in graphene, and is measurable
experimentally.Comment: 5 pages, 2 figure
Relationship between the symmetry energy and the single-nucleon potential in isospin-asymmetric nucleonic matter
In this contribution, we review the most important physics presented
originally in our recent publications. Some new analyses, insights and
perspectives are also provided. We showed recently that the symmetry energy
and its density slope at an arbitrary density
can be expressed analytically in terms of the magnitude and momentum dependence
of the single-nucleon potentials using the Hugenholtz-Van Hove (HVH) theorem.
These relationships provide new insights about the fundamental physics
governing the density dependence of nuclear symmetry energy. Using the isospin
and momentum (k) dependent MDI interaction as an example, the contribution of
different terms in the single-nucleon potential to the and
are analyzed in detail at different densities. It is shown that the
behavior of is mainly determined by the first-order symmetry
potential of the single-nucleon potential. The density
slope depends not only on the first-order symmetry potential
but also the second-order one . Both the
and at normal density are
constrained by the isospin and momentum dependent nucleon optical potential
extracted from the available nucleon-nucleus scattering data. The
especially at high density and momentum affects
significantly the , but it is theoretically poorly understood and
currently there is almost no experimental constraints known.Comment: 9 pages, 6 figures, Review paper, Contribution to the "Topical Issue"
on "Nuclear Symmetry Energy" in European Physical Journal
Why is the nuclear symmetry energy so uncertain at supra-saturation densities?
Within the interacting Fermi gas model for isospin asymmetric nuclear matter,
effects of the in-medium three-body interaction and the two-body short-range
tensor force due to the meson exchange as well as the short-range
nucleon correlation on the high-density behavior of the nuclear symmetry energy
are demonstrated respectively in a transparent way. Possible physics origins of
the extremely uncertain nuclear symmetry energy at supra-saturation densities
are discussed.Comment: Added discussions and revised format. Version to appear in Phys. Rev.
C (2010
An improved single particle potential for transport model simulations of nuclear reactions induced by rare isotope beams
Taking into account more accurately the isospin dependence of nucleon-nucleon
interactions in the in-medium many-body force term of the Gogny effective
interaction, new expressions for the single nucleon potential and the symmetry
energy are derived. Effects of both the spin(isospin) and the density
dependence of nuclear effective interactions on the symmetry potential and the
symmetry energy are examined. It is shown that they both play a crucial role in
determining the symmetry potential and the symmetry energy at supra-saturation
densities. The improved single nucleon potential will be useful for simulating
more accurately nuclear reactions induced by rare isotope beams within
transport models.Comment: 6 pages including 6 figures
Probing isospin- and momentum-dependent nuclear effective interactions in neutron-rich matter
The single-particle potentials for nucleons and hyperons in neutron-rich
matter generally depends on the density and isospin asymmetry of the medium as
well as the momentum and isospin of the particle. It further depends on the
temperature of the matter if the latter is in thermal equilibrium. We review
here the extension of a Gogny-type isospin- and momentum-dependent interaction
in several aspects made in recent years and their applications in studying
intermediate-energy heavy ion collisions, thermal properties of asymmetric
nuclear matter and properties of neutron stars. The importance of the isospin-
and momentum-dependence of the single-particle potential, especially the
momentum dependence of the isovector potential, is clearly revealed throughout
these studies.Comment: 27 pages, 19 figures, 1 table, accepted version to appear in EPJA
special volume on Nuclear Symmetry Energ
- …