1,682 research outputs found
Chiral pion-nucleon dynamics in finite nuclei: spin-isospin excitations
The nuclear density functional framework, based on chiral dynamics and the
symmetry breaking pattern of low-energy QCD, is extended to the description of
collective nuclear excitations. Starting from the relativistic point-coupling
Lagrangian previously introduced [Nucl. Phys. A770 (2006) 1], the
proton-neutron (quasiparticle) random phase approximation is formulated and
applied to investigate the role of chiral pion-nucleon dynamics in excitation
modes involving spin and isospin degrees of freedom, e.g. isobaric analog
states and Gamow-Teller resonances.Comment: 17 pages, 6 figures, elsart class. Minor revisions, Nuclear Physics A
in prin
An assessment of age determination methods for captured passerine birds
Various methods of determining age of passerine birds, using eye color, shape of flight feathers, plumage color patterns, etc. are presented in handbooks for bird banders, such as Pyle, et al., Identification Guide to North American Passerines (1987). We compared several such methods with the standard, reliable (but time-consuming) method, skulling , in 22 species of passerines captured and banded during Fall 1994, in a general netting operation at the University of Wisconsin-Milwaukee Field Station. In many species these methods were in agreement; however in 10 species there was substantial disagreement, especially involving buffy covert tips in thrushes and shape of rectrices or primary remiges in warblers. Since members of these groups are caught in large numbers, it is important to reevaluate these criteria and find more reliable methods
Latitude dependence of ionospheric electron content
Ionospheric electron content calculation method applied to Faraday fading signal
Nonlocal Polyakov-Nambu-Jona-Lasinio model and imaginary chemical potential
With the aim of setting constraints for the modeling of the QCD phase
diagram, the phase structure of the two-flavor Polyakov-loop extended Nambu and
Jona-Lasinio (PNJL) model is investigated in the range of imaginary chemical
potentials () and compared with available lattice QCD
results. The calculations are performed using the advanced nonlocal version of
the PNJL model with the inclusion of vector-type quasiparticle interactions
between quarks, and with wave-function-renormalization corrections. It is
demonstrated that the nonlocal PNJL model reproduces important features of QCD
at finite , such as the Roberge-Weiss (RW) periodicity and the
RW transition. Chiral and deconfinement transition temperatures for
turn out to coincide both at zero chemical potential and at finite
. Detailed studies are performed concerning the RW endpoint and
its neighborhood where a first-order transition occurs.Comment: 26 page, 13 figure, typo corrected, some references added and
corrected, one figure updated, version accepted for publication in Phys. Rev.
Hypernuclear single particle spectra based on in-medium chiral SU(3) dynamics
A previously derived relativistic energy density functional for nuclei, based
on low-energy in-medium chiral dynamics, is generalized to implement
constraints from chiral SU(3) effective field theory and applied to
hypernuclei. Density-dependent central and spin-orbit mean fields are
calculated for a hyperon using the SU(3) extension of in-medium
chiral perturbation theory to two-loop order. Long range
interactions arise from kaon-exchange and from two-pion-exchange with a
hyperon in the intermediate state. Short-distance dynamics is encoded
in contact interactions. They include scalar and vector mean fields reflecting
in-medium changes of quark condensates, constrained by QCD sum rules. The
single particle orbitals are computed for a series of hypernuclei
from C to Pb. The role of a surface
(derivative) term is studied. Its strength is found to be compatible with a
corresponding estimate from in-medium chiral perturbation theory. Very good
agreement with hypernuclear spectroscopic data is achieved. The smallness of
the -nuclear spin-orbit interaction finds a natural explanation in
terms of an almost complete cancellation between short-range scalar/vector
contributions and longer range terms generated by two-pion exchange.Comment: 30 pages, 5 figures, elsart class, minor corrections, to be published
in Nuclear Physics
Quasiparticle Description of Hot QCD at Finite Quark Chemical Potential
We study the extension of a phenomenologically successful quasiparticle model
that describes lattice results of the equation of state of the deconfined phase
of QCD for Tc <= T < 4 Tc, to finite quark chemical potential mu. The phase
boundary line Tc(mu), the pressure difference (p(T,mu)-p(T,mu=0))/T^4 and the
quark number density nq(T,mu)/T^3 are calculated and compared to recent lattice
results. Good agreement is found up to quark chemical potentials of order mu =
Tc.Comment: 12 pages, 7 figures; added reference
Possibility of s-wave pion condensates in neutron stars revisited
We examine possibilities of pion condensation with zero momentum (s-wave
condensation) in neutron stars by using the pion-nucleus optical potential U
and the relativistic mean field (RMF) models. We use low-density
phenomenological optical potentials parameterized to fit deeply bound pionic
atoms or pion-nucleus elastic scatterings. Proton fraction (Y_p) and electron
chemical potential (mu_e) in neutron star matter are evaluated in RMF models.
We find that the s-wave pion condensation hardly takes place in neutron stars
and especially has no chance if hyperons appear in neutron star matter and/or
b_1 parameter in U has density dependence.Comment: 4 pages, 3 figures, REVTe
Nuclear Many-Body Dynamics constrained by QCD and Chiral Symmetry
We present a novel description of nuclear many-body systems, both for nuclear
matter and finite nuclei, emphasizing the connection with the condensate
structure of the QCD ground state and spontaneous chiral symmetry breaking.
Lorentz scalar and vector mean-fields are introduced in accordance with QCD sum
rules. Nuclear binding arises from pionic fluctuations, using in-medium chiral
perturbation theory up to three-loop order. Ground state properties of O
and Ca are calculated. The built-in QCD constraints reduce the number of
input parameters significantly in comparison with purely phenomenological
relativistic mean-field approaches.Comment: 6 pages, 3 figures, to be published in European Physical Journal
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