R. Aguirre

Density dependence of the MIT bag parameters from the field theory of hadrons.

Abstract A self-consistent description of the MIT bag parameters as functions of the nuclear matter density is presented. The subnuclear degrees of freedom are treated in the Quark-Meson Coupling Model, considering the equilibrium conditions for the bag in the nuclear medium. The hadronic interaction is described in the framework of the quantum field theory of hadrons through several models. We have obtained the behavior of the bag radius and the bag parameters B and z 0 , taking their derivatives with respect to the mean field value of the scalar meson as free parameters. A discussion on the variation range of these derivatives is given.

Equation of state of hadronic matter with dibaryons in an effective quark model

The equation of state of symmetric nuclear matter with the inclusion of non-strange dibaryons is studied. They pay special attention to the existence of a dibaryon condensate at zero temperature. These calculations have been performed in an extended quark-meson coupling model with density-dependent parameters, which takes into account the finite size of nucleons and dibaryons. A first-order phase-transition to pure dibaryon matter has been found. The corresponding critical density is strongly dependent on the value of the dibaryon mass. The density behavior of the nucleon and dibaryon effective masses and confining volumes have also been discussed.

Nuclear superfluidity in isospin asymmetric matter within the Skyrme model

The phase diagram of the superfluid phase coupled to spin singlet (S=0) and isospin triplet (T=1) states in infinite nuclear matter is analyzed within the nonrelativistic Skyrme model. We use an approach that allows a unified and consistent treatment of the particle-hole and particle-particle channels. The gap equation is solved for the full range of accessible densities, isospin asymmetries, and temperatures. The characteristic features of each of the components Tz=0, +1, -1 are emphasized. The search for signatures of a BCS-BEC crossover yields negative results within the scheme proposed.

The linear σ-ω model in the thermo field dynamics☆

Abstract The relativistic linear σ-ω model is used to describe symmetric nuclear matter at finite temperature. The thermo field dynamics is applied to compute, perturbatively, quantum corrections to the temperature-dependent Hartree mean field. The effect of these corrections upon nuclear-matter properties at saturation is studied.

The Zimanyi and Moszkowski model in thermo field dynamics

Abstract The effective Lagrangian introduced by Zimanyi and Moszkowski is used to calculate the equation of state of symmetric nuclear matter at finite densities and temperatures. The model is treated in the mean field approximation and one-loop perturbative corrections are added to the mean field value of relevant propagators. Green functions for baryons and mesons are constructed in the framework of thermo field dynamics. An effective residual interaction, with coupling coefficients which are dependent on density and temperature, is introduced. This effective coupling is used to calculate perturbative corrections to the baryon mass, the equation of state and the compressibility of the system.

Neutron matter under strong magnetic fields: A comparison of models

Fil: Aguirre, Ricardo Miguel. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Fisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Fisica La Plata; Argentina

Nuclear collective excitations in a two-phase coexistence region

The relation between collective modes and the phase transition in low density nuclear matter is examined. The dispersion relations for collective modes in a linear approach are evaluated within a LandauFermi liquid scheme by assuming coexisting phases in thermodynamical equilibrium. Temperature and isospin composition are taken as relevant parameters. The in-medium nuclear interaction is taken from a recently proposed density functional model. We found significative modifications in the energy spectrum, within certain range of temperatures and isospin asymmetry, due to the separation of matter into independent phases. We conclude that detailed calculations should not neglect this effect. PACS: 21.30.Fe, 21.65.-f, 71.10.Ay, 26.60.-c ∗This work was partially supported by the CONICET, Argentina.

Landau parameters for isospin asymmetric nuclear matter based on a relativistic model of composite and finite extension nucleons

We study the properties of cold asymmetric nuclear matter at high density, applying the quark meson coupling model with excluded volume corrections in the framework of the Landau theory of relativistic Fermi liquids. We discuss the role of the finite spatial extension of composite baryons on dynamical and statistical properties such as the Landau parameters, the compressibility, and the symmetry energy. We have also calculated the low-lying collective eigenfrequencies arising from the collisionless quasiparticle transport equation, considering both unstable and stable modes. An overall analysis of the excluded volume correlations on the collective properties is performed.

Compatibility of QCD sum-rules and hadron field theory in a dense medium

The compatibility of the QCD sum rules and effective hadronic models predictions are examined. For this purpose we have considered the results for the nucleon self-energy in a dense hadronic environment provided by two independent QCD sum-rules calculations. They are immersed in a theory of hadronic fields giving rise to non-linear interactions, whose vertices are parameterized in different ways. Although all of them reproduce the self-energy used as input, very different descriptions of nuclear observables are obtained. Only under very definite circumstances we have found an acceptable agreement with the nuclear matter properties. To achieve this, phenomenological parameters are not required at all.

Collective modes in strange and isospin-asymmetric hadronic matter

Abstract We study the propagation of non-strange and strange meson modes in hadronic matter considering both isospin and strangeness mixing induced by quantum fluctuations in the medium. Baryons are described using the quark–meson coupling model extended to include interactions of strange quarks. In particular, we evaluate the dependence of the meson masses on the baryonic density, the strangeness fraction and the isospin asymmetry of the medium. We have found a considerable admixture of strangeness and isospin in the σ-mode in the high density regime.