3,606 research outputs found
Scalar response of the nucleon chiral symmetry and nuclear matter properties
In this talk we present a description of nuclear binding in a chiral approach
based on the existence of a chiral invariant scalar field associated with the
generation of the masses through spontaneous chiral symmetry breaking. We
discuss the emergence of such a field on the example of the NJL model. We also
incorporate the effect of confinement at the level of the nucleon substructure
to stabilize nuclear matter. In a particular quark-diquark model we illustrate
the simutaneous influences of spontaneous chiral symmetry breaking and
confinement on the nucleon mass and on the nuclear matter description.Comment: Talk given by G. chanfray at "Achievements and New Directions in
Subatomic Physics: Workshop in Honour of Tony Thomas' 60th Birthday Adelaide,
South Australia. February 15 - February 19, 2010"
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
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
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.
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
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
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
Energy reconstruction effects in neutrino oscillation experiments and implications for the analysis
Data on neutrino oscillation often involve reconstructed neutrino energies
while the analysis implies the real neutrino energy. The corrections
corresponding to the transformation from real to reconstructed energy are
discussed in the case of Cherenkov detectors where multinucleon events appear
as quasielastic ones. These corrections show up as a tendency for the events to
escape the region of high flux, with a clear preference for the low energy
side. This is an effect of the multinucleon component of the quasielastic cross
section. We have applied our corrections to the T2K and MiniBooNE data for
electron appearance or disappearance data. We show that the inclusion
of this correction in the analysis is expected to lead to an increase of the
best fit oscillation mass parameters, particularly pronounced for the MiniBooNE
neutrino data. This inclusion in the analysis of the MiniBooNE neutrino data
should improve the compatibility with the existing constraints
The quark condensate at finite temperature
The temperature evolution of the quark condensate is studied using three
different methods. In the spirit of a many-body approach we make an expansion
in the scalar density up to second order. Our result is consistent chiral
perturbation theory to two-loop order.Comment: Latex 14 pages + 1 figure (postscript
Neutrino energy reconstruction problems and neutrino oscillations
We discuss the accuracy of the usual procedure for neutrino energy
reconstruction which is based on the quasielastic kinematics. Our results are
described in terms of a probability distribution for a real neutrino energy
value. Several factors are responsible of the deviations from the reconstructed
value. The main one is the multinucleon component of the neutrino interaction
which in the case of Cherenkov detectors enters as a quasielastic cross
section, increasing the mean neutrino energy which can differ appreciably from
the reconstructed value. As an application we derive, for excess electron
events attributed to the conversion of muon neutrinos, the true neutrino energy
distribution based on the experimental one which is given in terms of the
reconstructed value. The result is a reshaping effect. For MiniBooNE the low
energy peak is suppressed and shifted at higher energies, which may influence
the interpretation in terms of oscillation. For T2K at the Super Kamiokande far
detector the reshaping translates into a narrowing of the energy distribution
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