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 $\sigma$ and $\omega$ 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 $\sigma$ and $\omega$ exchange using a formulation of the $\sigma$ 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 $\nu_\mu$ 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