9,016 research outputs found
Modifications of the Rho Meson from the Virtual Pion Cloud in Hot and Dense Matter
The modification of the rho-meson self-energy due to the coupling to
in-medium pions is calculated consistently at finite baryon density and
temperature, keeping the full 3-momentum dependence in a gauge invariant way.
As a function of nucleon density, the rho-meson spectral function is strongly
enhanced in the invariant mass region M < 650 MeV, while the maximum, i.e. the
pole mass, is slightly shifted upwards. As a function of temperature, for fixed
nucleon density, the imaginary part of the self-energy increases further due to
Bose-enhancement. At the same time the mass shift from the real part becomes
very large. As a consequence of these medium effects, the dilepton rate in the
low-mass region M < 650 MeV increases strongly, while the peak at M = 770 MeV
disappears.Comment: 18 pages, 9 figures; resonance contributions adde
Is Rho-Meson Melting Compatible with Chiral Restoration?
Utilizing in-medium vector spectral functions which describe dilepton data in
ultra-relativistic heavy-ion collisions, we conduct a comprehensive evaluation
of QCD and Weinberg sum rules at finite temperature. The starting point is our
recent study in vacuum, where the sum rules have been quantitatively satisfied
using phenomenological axial-/vector spectral functions which describe hadronic
tau-decay data. In the medium, the temperature dependence of condensates and
chiral order parameters is taken from thermal lattice QCD where available, and
otherwise estimated from a hadron resonance gas. Since little is known about
the in-medium axial-vector spectral function, we model it with a Breit-Wigner
ansatz allowing for smooth temperature variations of its width and mass
parameters. Our study thus amounts to testing the compatibility of the
-broadening found in dilepton experiments with (the approach toward)
chiral restoration, and thereby searching for viable in-medium axial-vector
spectral functions.Comment: 8 pages, 4 figures, updated to be consistent with published versio
The Influence of Reaction Rates on the Final p-Abundances
The astrophysical p-process is responsible for the origin of the proton rich
nuclei,which are heavier than iron. A huge network involving thousands of
reaction rates is necessary to calculate the final p-abundances. But not all
rates included in the network have a strong influence on the p-nuclei
abundances. The p-process was investigated using a full nuclear reaction
network for a type II supernovae explosion when the shock front passes through
the O/Ne layer. Calculations were done with a multi-layer model adopting the
seed of a pre-explosion evolution of a 25 mass star. In extensive simulations
we investigated the impact of single reaction rates on the final p-abundances.
The results are important for the strategy of future experiments in this field.Comment: 4 page
A Microscopic Calculation of Photoabsorption Cross Sections on Protons and Nuclei
A recently developed model for -meson propagation in dense hadronic
matter is applied to total photoabsorption cross sections in -proton
and -nucleus reactions. Within the vector dominance model the photon
coupling to the virtual pion cloud of the nucleon, two-body meson-exchange
currents, as well as -nucleon resonances are included. Whereas the
reaction is determined by the low-density limit of the model, higher
orders in the nuclear density are important to correctly account for the
experimental spectra observed on both light and heavy nuclei over a wide range
of photon energies, including the region below the pion threshold. In
connection with soft dilepton spectra in high-energy heavy-ion collisions we
emphasize the importance of photoabsorption to further constrain the parameters
of the model.Comment: 10 pages RevTeX, 2 eps-figure
Momentum Dependence of the Pion Cloud for Rho Mesons in Nuclear Matter
We extend hadronic models for rho-meson propagation in cold nuclear matter
via coupling to in-medium pions to include finite three-momentum. Special care
is taken to preserve gauge invariance. Consequences for photoabsorption on the
proton and on nuclei as well as for the dilepton production in relativistic
heavy-ion collisions are discussed.Comment: 32 pages, 18 figures. Corrected version, accepted for publication in
Nucl. Phys.
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