1,672 research outputs found
Model independent constraints from vacuum and in-medium QCD Sum Rules
We discuss QCD sum rule constraints based on moments of vector meson spectral
distributions in the vacuum and in a nuclear medium. Sum rules for the two
lowest moments of these spectral distributions do not suffer from uncertainties
related to QCD condensates of dimension higher than four. We exemplify these
relations for the case of the omega meson and discuss the issue of in-medium
mass shifts from this viewpoint.Comment: 6 pages, 2 figures, to appear in Eur. Phys. J.
Thermal Dileptons from Quark and Hadron Phases of an Expanding Fireball
A fireball model with time evolution based on transport calculations is used
to examine the dilepton emission rate of an ultra-relativistic heavy-ion
collision. We assume a transition from hadronic matter to a quark-gluon plasma
at a critical temperature T_C between 130-170 MeV. We include thermal
corrections to the hadronic spectra below T_C and use perturbation theory above
T_C. The sensitivity of the spectra with respect to the freeze-out temperature,
the initial fireball temperature and the critical temperature is investigated.Comment: 14 pages, 5 figures; paragraph and one figure added; version to
appear in Eur. Phys. J.
Chiral Fermi liquid approach to neutron matter
We present a microscopic calculation of the complete quasiparticle
interaction, including central as well as noncentral components, in neutron
matter from high-precision two- and three-body forces derived within the
framework of chiral effective field theory. The contributions from two-nucleon
forces are computed in many-body perturbation theory to first and second order
(without any simplifying approximations). In addition we include the
leading-order one-loop diagrams from the N2LO chiral three-nucleon force, which
contribute to all Fermi liquid parameters except those associated with the
center-of-mass tensor interaction. The relative-momentum dependence of the
quasiparticle interaction is expanded in Legendre polynomials up to L=2.
Second-order Pauli blocking and medium polarization effects act coherently in
specific channels, namely for the Landau parameters f_1, h_0 and g_0, which
results in a dramatic increase in the quasiparticle effective mass as well as a
decrease in both the effective tensor force and the neutron matter spin
susceptibility. For densities greater than about half nuclear matter saturation
density \rho_0, the contributions to the Fermi liquid parameters from the
leading-order chiral three-nucleon force scale in all cases approximately
linearly with the nucleon density. The largest effect of the three-nucleon
force is to generate a strongly repulsive effective interaction in the
isotropic spin-independent channel. We show that the leading-order chiral
three-nucleon force leads to an increase in the spin susceptibility of neutron
matter, but we observe no evidence for a ferromagnetic spin instability in the
vicinity of the saturation density \rho_0. This work sets the foundation for
future studies of neutron matter response to weak and electromagnetic probes
with applications to neutron star structure and evolution.Comment: 21 pages, 6 figures, 5 table
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