13 research outputs found
Pions in isospin asymmetric matter and nuclear Drell-Yan scattering
Using a self-consistent delta-hole model the pion propagation in isospin
asymmetric nuclear matter is studied. In neutron-rich matter, corresponding to
heavy nuclei, a significant difference in positive and negative pion light-cone
distributions is obtained leading to a nuclear enhancement of up antiquark
distribution compared to the down antiquark one. This means that the sea-quark
asymmetry in the free nucleon cannot be extracted model independently from an
experiment on a neutron-rich nucleus.Comment: 10 pages, 3 figures (included), Latex 2.09, uses elsart.sty, epsf.st
Open-charm systems in cold nuclear matter
We study the spectral distributions of charmed meson with quantum
numbers in cold nuclear matter applying a self-consistent and covariant
many-body approach established previously for the nuclear dynamics of kaons. At
leading orders the computation requires as input the free-space two-body
scattering amplitudes only. Our results are based on the s-wave meson-nucleon
amplitudes obtained recently in terms of a coupled-channel approach. The
amplitudes are characterized by the presence of many resonances in part so far
not observed. This gives rise to an intriguing dynamics of charmed mesons in
nuclear matter. At nuclear saturation density we predict a pronounced two-mode
structure of the mesons with a main branch pushed up by about 32 MeV. The
lower branch reflects the coupling to two resonance-hole states that are almost
degenerate. For the we obtain a single mode pushed up by about 18 MeV
relative to the vacuum mode. Most spectacular are the results for the
meson. The presence of an exotic resonance-hole state gives rise to a rather
broad and strongly momentum dependent spectral distribution.Comment: 11 pages, 3 figure
Antikaons and hyperons in nuclear matter with saturation
We evaluate the antikaon and hyperon spectral functions in a self-consistent
and covariant many-body approach. The computation is based on coupled-channel
dynamics derived from the chiral SU(3) Lagrangian. A novel subtraction scheme
is developed that avoids kinematical singularities and medium-induced power
divergencies all together. Scalar and vector mean fields are used to model
nuclear binding and saturation. The effect of the latter is striking for the
antikaon spectral function that becomes significantly more narrow at small
momenta. Attractive mass shifts of about 30 and 40 MeV are predicted for the
Lambda(1405) and Sigma(1385) resonances. Once scalar and vector mean fields for
the nucleon are switched on the Lambda(1520) resonances dissolves almost
completely in nuclear matter. All together only moderate attraction is
predicted for the nuclear antikaon systems at saturation density. However, at
larger densities we predict a sizable population of soft antikaon modes that
arise from the coupling of the antikaon to a highly collective Lambda(1115)
nucleon-hole state. This may lead to the formation of exotic nuclear systems
with strangeness and antikaon condensation in compact stars at moderate
densities.Comment: 49 pages, 13 figures, The revised manuscript contains additional
material at twice nuclear saturation density. An unexpected and novel
mechanism is unravelled that may have dramatic implications on the formation
of exotic nuclear systems with strangeness and antikaon condensation in
compact star
Self consistent and covariant propagation of pions, nucleon and isobar resonances in cold nuclear matter
We evaluate the in-medium spectral functions for pions, nucleon and isobar
resonances in a self consistent and covariant manner. The calculations are
based on a recently developed formulation which leads to predictions in terms
of the pion-nucleon scattering phase shifts and a set of Migdal parameters
describing important short range correlation effects. We do not observe
significant softening of pion modes if we insist on reasonable isobar resonance
properties but predict a considerable broadening of the N(1440) and N(1520)
resonances in nuclear matter. Contrasted results are obtained for the s-wave
N(1535) and N(1650) resonances which are affected by a nuclear environment very
little. The properties of slowly moving isobar's in nuclear matter are found to
depend very sensitively on a soft form factor in the piNN vertex, which is not
controlled by the piN scattering data.Comment: 20 pages, 7 figure, revised manuscrip
Dilepton Production at SPS-energy Heavy Ion Collisions
The production of dileptons is studied within a hadronic transport model. We
investigate the sensitivity of the dilepton spectra to the initial
configuration of the hadronic phase in a ultrarelativistic heavy ion collision.
Possible in medium correction due to the modifications of pions and the pion
form factor in a hadronic gas are discussed.Comment: Dedicated to Gerry Brown in honor of the 32nd celebration of his 39th
birthday. 31 pages Latex including 13 eps-figures, uses psfig.sty and
epsf.st
The hyperon-nucleon interaction: conventional versus effective field theory approach
Hyperon-nucleon interactions are presented that are derived either in the
conventional meson-exchange picture or within leading order chiral effective
field theory. The chiral potential consists of one-pseudoscalar-meson exchanges
and non-derivative four-baryon contact terms. With regard to meson-exchange
hyperon-nucleon models we focus on the new potential of the Juelich group,
whose most salient feature is that the contributions in the scalar--isoscalar
(\sigma) and vector--isovector (\rho) exchange channels are constrained by a
microscopic model of correlated \pi\pi and KKbar exchange.Comment: 28 pages, 8 figures, submitted to Lecture Notes in Physic
On kinematical constraints in boson-boson systems
We consider the scattering of two-bosons with negative parity and spin 0 or
1. Starting from helicity partial-wave scattering amplitudes we derive
transformations that eliminate all kinematical constraints. Such amplitudes are
expected to satisfy partial-wave dispersion relations and therefore provide a
suitable basis for data analysis and the construction of effective field
theories. Our derivation relies on a decomposition of the various scattering
amplitudes into suitable sets of invariant functions. A novel algebra was
developed that permits the efficient computation of such functions in terms of
computer algebra codes.Comment: 14 pages, 8 table
Self consistent propagation of hyperons and antikaons in nuclear matter based on relativistic chiral SU(3) dynamics
We evaluate the antikaon spectral density in isospin symmetric nuclear matter. The in-medium antikaon-nucleon scattering process and the antikaon propagation is treated in a self consistent and relativistic manner where a maximally scheme-independent formulation is derived by performing a partial density resummation in terms of the free-space antikaon-nucleon scattering amplitudes. The latter amplitudes are taken from a relativistic and chiral coupled-channel SU(3) approach which includes s-, p- and d-waves systematically. Particular care is taken on the proper evaluation of the in-medium mixing of the partial waves. Our analysis establishes a rich structure of the antikaon spectral function with considerable strength at small energies. At nuclear saturation density we predict attractive mass shifts for the #LAMBDA#(1405), #SIGMA#(1385) and #LAMBDA#(1520) of about 130 MeV, 60 MeV and 100 MeV respectively. The hyperon states are found to exhibit at the same time an increased decay width of about 150 MeV for the s-wave #LAMBDA#(1405), 70 MeV for the p-wave #SIGMA#(1385) and 100 MeV for the d-wave #LAMBDA#(1520) resonance. (orig.)Available from TIB Hannover: RO 801(2001-18) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Self consistent and covariant propagation of pions, nucleon and isobar resonances in cold nuclear matter
We evaluate the in-medium spectral functions for pions, nucleon and isobar resonances in a self consistent and covariant manner. The calculations are based on a recently developed formulation which leads to predictions in terms of the pion-nucleon scattering phase shifts and a set of Migdal parameters describing important short range correlation effects. We do not observe any significant softening of pion modes if we insist on reasonable isobar resonance properties but predict a considerable broadening of the N(1440) and N(1520) resonances in nuclear matter. (orig.)Available from TIB Hannover: RO 801(03-18) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman