280 research outputs found
Constraints on nuclear matter properties from QCD susceptibilities
We establish the interrelation between the QCD scalar response of the nuclear
medium and its response to a scalar probe coupled to nucleons, such as the
scalar meson responsible for the nuclear binding. The relation that we derive
applies at the nucleonic as well as at the nuclear levels. Non trivial
consequences follow. In particular it opens the possibility of relating medium
effects in the scalar meson exchange or three-body forces of nuclear physics to
QCD lattice studies of the nucleon massComment: Submitted to EPJ
Pions in the nuclear medium
We discuss various aspects of pion physics in the nuclear medium. We first
study s-wave pion-nucleus interaction in connection with chiral symmetry
restoration and quark condensate in the nuclear medium. We then adress the
question of p-wave pion-nucleus interaction and collective pionic modes in
nuclei and draw the consequences for in medium correlations especially
in the scalar-isoscalar channel. We finally discuss the modification of the rho
meson mass spectrum at finite density and/or temperature in connection with
relativistic heavy ion collisions.Comment: 13 pages, latex, 8 figures eps (talk given at the Workshop, MESON'96,
Cracow, Poland, 14 May 96
Two-pion production processes, chiral symmetry and NN interaction in the medium
We study the two-pion propagator in the nuclear medium. This quantity appears
in the T-matrix and we show that it also enters the QCD scalar
susceptibility. The medium effects on this propagator are due to the influence
of the individual nucleon response to a scalar field through their pion clouds.
This response is appreciably increased by the nuclear environment. It produces
an important convergence effect between the scalar and pseudoscalar
susceptibilities, reflecting the reshaping of the scalar strengh observed in
production experiments. While a large modification of the
propagator follows, due to its coupling to two pion states, we show that the NN
potential remains instead unaffected.Comment: 14 pages, 4 figures, submitted to EPJ
In-medium modification of the isovector pion-nucleon amplitude
We study the in-medium modification of the isovector pi N amplitude using a
non-linear representation of the sigma model but keeping the scalar degree of
freedom. We check that our result does not depend on the representation. We
discuss the connection with other approaches based on chiral perturbation
theory.Comment: 7 page
Nuclear matter saturation in a relativistic chiral theory and QCD susceptibilities
We study a chiral relativistic theory of nuclear matter aimed at the
desciption of both the binding and saturation properties and the QCD
properties, quark condensate and QCD susceptibilities. For this purpose the
nucleon scalar response of the quark-meson coupling model is introduced in the
linear sigma model. The consequences for the nuclear and the QCD scalar
susceptibilities are discussed.Comment: 9 pages, 3 figures, sumitted to Physical Review
QCD susceptibilities and nuclear matter saturation in a chiral theory: inclusion of pion loops
We derive the equation of state of symmetric nuclear matter in a relativistic
theory with and exchange. We take a chiral version of this
model which insures all the chiral constraints. Going beyond the mean field
approach we introduce the effects of the pion loops. For the parameters of the
model, in order to fix those linked to pion exchange, we exploit the most
recent information on the short-range part of the spin-isospin interaction. For
those linked to the scalar meson exchange we make use of an analysis of lattice
results on the nucleon mass evolution with the quark mass. With these inputs we
are able reach a correct description of the saturation properties. From the
equation of state of symmetric nuclear matter we alsoderive the density
dependence of the quark condensate and of the QCD susceptibilities
Chiral symmetry, scalar field and confinement : from nucleon structure to nuclear matter
We discuss the relevance of the scalar modes appearing in chiral theories
with spontaneous symmetry breaking such as the NJL model for nuclear matter
studies. We show that it depends on the relative role of chiral symmetry
breaking and confinement in the nucleon mass origin. It is only in the case of
a mixed origin that nuclear matter can be stable and reach saturation. We
describe models of nucleon structure where this balance is achieved. We show
how chiral constarints and confinement modify the QCD sum rules for the mass
evolution in nuclear matter.Comment: talk given by G. Chanfray at the Chiral10 WORKSHOP, Valencia (Spain),
June 21-24, 201
From QCD to nuclear matter saturation
We discuss a relativistic chiral theory of nuclear matter with and
exchange using a formulation of the model in which all the
chiral constraints are automatically fulfilled. We establish a relation between
the nuclear response to the scalar field and the QCD one which includes the
nucleonic parts. It allows a comparison between nuclear and QCD information.
Going beyond the mean field approach we introduce the effects of the pion loops
supplemented by the short-range interaction. The corresponding Landau-Migdal
parameters are taken from spin-isospin physics results. The parameters linked
to the scalar meson exchange are extracted from lattice QCD results. These
inputs lead to a reasonable description of the saturation properties,
illustrating the link between QCD and nuclear physics. We also derive from the
corresponding equation of state the density dependence of the quark condensate
and of the QCD susceptibilities.Comment: Talk given by M. Ericson at the Yukawa International Seminar (YKIS)
2006 "New frontiers in QCD", Kyoto, Japo
Fluctuations of the quark densities in nuclei
We study the static scalar susceptibility of the nuclear medium, i.e., the
change of the quark condensate for a small modification of the quark mass. In
the linear sigma model it is linked to the in-medium sigma propagator. At
ordinary nuclear densities, when chiral symmetry is spontaneously broken, the
scalar susceptibility is distinct from the pseudoscalar one, which is linked to
the fluctuations of the quark pseudoscalar density. We show that the
pseudoscalar one, which is large in the vacuum, owing to the smallness of the
pion mass, follows the density evolution of the quark condensate and thus
decreases. The scalar one instead increases due to the mixing with the softer
modes of the nucleon-hole excitations. At normal nuclear matter density the two
susceptibilities become much closer, a partial chiral symmetry restoration
effect as they become equal when the full restoration is achieved.Comment: 9 pages, 1 figure, submitted to Phys. Rev.
Relativistic Chiral Theory of Nuclear Matter and QCD Constraints
We present a relativistic chiral theory of nuclear matter which includes the
effect of confinement. Nuclear binding is obtained with a chiral invariant
scalar background field associated with the radial fluctuations of the chiral
condensate Nuclear matter stability is ensured once the scalar response of the
nucleon depending on the quark confinement mechanism is properly incorporated.
All the parameters are fixed or constrained by hadron phenomenology and lattice
data. A good description of nuclear saturation is reached, which includes the
effect of in-medium pion loops. Asymmetry properties of nuclear matter are also
well described once the full rho meson exchange and Fock terms are included.Comment: Talk given by G. Chanfray at PANIC 08, Eilat (Israel), november
10-14, 200
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