3,783 research outputs found
Potentials between heavy-light mesons from lattice and inverse scattering theory
We extend our investigation of heavy-light meson-meson interactions to a
system consisting of a heavy-light meson and the corresponding antiparticle. An
effective potential is obtained from meson-antimeson Green-functions computed
in a quenched simulation with staggered fermions. Comparisons with a simulation
using an tree-level and tadpole improved gauge action and a full QCD
simulation show that lattice discretization errors and dynamical quarks have no
drastic influence. Calculations from inverse scattering theory propose a
similar shape for potentials.Comment: 3 pages, 5 EPS figures, Poster presented at "Lattice'97", to appear
in the proceeding
Numerical solution of the color superconductivity gap in a weak coupling constant
We present the numerical solution of the full gap equation in a weak coupling
constant . It is found that the standard approximations to derive the gap
equation to the leading order of coupling constant are essential for a secure
numerical evaluation of the logarithmic singularity with a small coupling
constant. The approximate integral gap equation with a very small should be
inverted to a soft integral equation to smooth the logarithmic singularity near
the Fermi surface. The full gap equation is solved for a rather large coupling
constant . The approximate and soft integral gap equations are solved
for small values. When their solutions are extrapolated to larger
values, they coincide the full gap equation solution near the Fermi surface.
Furthermore, the analytical solution matches the numerical one up to the order
one O(1). Our results confirm the previous estimates that the gap energy is of
the order tens to 100 MeV for the chemical potential MeV. They
also support the validity of leading approximations applied to the full gap
equation to derive the soft integral gap equation and its analytical solution
near the Fermi surface.Comment: 7 pages+ 6 figs, Stanford, Frankfurt and Bethlehe
Gluons, tadpoles, and color neutrality in a two-flavor color superconductor
Considering cold, dense quark matter with two massless quark flavors, we
demonstrate how, in a self-consistent calculation in the framework of QCD, the
condensation of Cooper pairs induces a non-vanishing background color field.
This background color field has precisely the right magnitude to cancel tadpole
contributions and thus ensures overall color neutrality of the two-flavor color
superconductor.Comment: 10 pages, contribution to the proceedings of the Erice school
"Heavy-Ion Collisions from Nuclear to Quark Matter" 200
Positivity of High Density Effective Theory
We show that the effective field theory of low energy modes in dense QCD has
positive Euclidean path integral measure. The complexity of the measure of QCD
at finite chemical potential can be ascribed to modes which are irrelevant to
the dynamics at sufficiently high density. Rigorous inequalities follow at
asymptotic density. Lattice simulation of dense QCD should be possible using
the quark determinant calculated in the effective theory.Comment: 10 pages, Revised version, to appear in Rapid Communications of
Physical Review
A quark action for very coarse lattices
We investigate a tree-level O(a^3)-accurate action, D234c, on coarse
lattices. For the improvement terms we use tadpole-improved coefficients, with
the tadpole contribution measured by the mean link in Landau gauge.
We measure the hadron spectrum for quark masses near that of the strange
quark. We find that D234c shows much better rotational invariance than the
Sheikholeslami-Wohlert action, and that mean-link tadpole improvement leads to
smaller finite-lattice-spacing errors than plaquette tadpole improvement. We
obtain accurate ratios of lattice spacings using a convenient ``Galilean
quarkonium'' method.
We explore the effects of possible O(alpha_s) changes to the improvement
coefficients, and find that the two leading coefficients can be independently
tuned: hadron masses are most sensitive to the clover coefficient, while hadron
dispersion relations are most sensitive to the third derivative coefficient
C_3. Preliminary non-perturbative tuning of these coefficients yields values
that are consistent with the expected size of perturbative corrections.Comment: 22 pages, LaTe
Neutron stars and the transition to color-superconducting quark matter
We explore the relevance of color superconductivity inside a possible quark
matter core for the bulk properties of neutron stars. For the quark phase we
use an Nambu--Jona-Lasinio (NJL) type model, extended to include diquark
condensates. For the hadronic phase, a microscopic many-body model is adopted,
with and without strangeness content. In our calculations, a sharp boundary is
assumed between the hadronic and the quark phases. For NJL model parameters
fitted to vacuum properties we find that no star with a pure quark core does
exist. Nevertheless the presence of color superconducting phases can lower the
neutron star maximum mass substantially. In some cases, the transition to quark
matter occurs only if color superconductivity is present. Once the quark phase
is introduced, the value of the maximum mass stays in any case below the value
of two solar masses.Comment: 11 pages, 3 figures, v2: minor corrections in the text, layout of the
figures improved, references added, v3: transition densities from hadronic to
quark matter added, version accepted for publication in PL
U.S. Air Force Maintenance Group Aerial Ports: Strengths, Challenges, Opportunities, and Threats
In 2005 the Base Closure Realignment Commission and Secretary of Defense recommended joint basing; as an indirect result starting in 2009 and culminating the following year, Charleston, Dover, McChord, McGuire, and Travis maintenance groups (MXG) took command of aerial port squadrons (APS). Various entities have discussed at length the impact; however, there did not appear to be a documented hard look into the strengths, challenges, opportunities, and threats (SCOTs) which emerged. This study utilized the Delphi method to flesh out MXG APS SCOTs by anonymously surveying MXG and APS experts through three panel rounds. This study discovered and documented 24 SCOTs and viewed them through the Competing Values Framework (CVF) theoretical lens. The majority of the panel’s inputs concerning maintenance and aerial port entities fell on opposing sides of the CVF; which may explain why the panel, consisting of maintenance and APS leaders, did not reach strong consensus in two out of four SCOT categories. This study proposes creating a wing or standalone group to house the five aerial ports or altering the MXG title to be more representative of all squadrons assigned and ensuring at least one logistics readiness officer or aerial porter is on each MXG leadership team
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