Narrow Results

We study effects of temperature in hadron dense matter within a generalized relativistic mean field approach based on the naturalness of the various coupling constants of the theory, The Lagrangian density of our formulation contains the fundamental baryon octet, nonlinear self-couplings of the σ and δ meson fields coupled to the baryons and to the ω and ρ meson fields. By adjusting the model parameters, after inclusion in a consistent way of chemical equilibrium, baryon number and electric charge conservation, our model describes static bulk properties of ordinary nuclear matter and neutron stars. In the framework of the Sommerfeld approximation, we extend our approach to the T≠0 domain. The Sommerfeld approximation allows a drastic simplification of computational work while improving the capability of the theoretical analysis of the role of temperature on static properties of protoneutron stars. We perform the calculations by using our nonlinear model, which we extend by considering trapped neutrinos introduced into the formalism by fixing the lepton fraction. Integrating the Tolman–Oppenheimer–Volkoff equations we have obtained standard plots for the mass and radius of protoneutron stars as a function of the central density and temperature. Our predictions include the determination of an absolute value for the protoneutron star limiting mass at low and intermediate temperature regimes.

In the investigation of the role of naturalness in effective theory, we focus on dense hadronic matter in a generalized relativistic multi-baryon Lagrangian density mean field approach which contains nonlinear self-couplings of the σ and δ meson fields interacting with the fundamental baryon octet and with the ω and ϱ meson fields and compare its predictions with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coupling constants of the Lagrangian model; our investigation is limited however to the scalar sector of the theory. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we show that our approach represents a natural modelling of nuclear matter under the extreme conditions of density as found in the interior of neutron stars.

Based on non-crossed, crossed and correlated ππ exchanges with irreducible N, Δ intermediate states, we predict an isovector component for the σ meson. We study dense hadronic matter in a generalized relativistic mean field approach with nonlinear self-couplings of the I=0,1 components of the scalar field and compare its predictions for neutron star properties with results from different models found in the literature.

High density hadronic matter is studied in a generalized relativistic multi-baryon Lagrangian density mean field approach which contains nonlinear couplings of the σ, ω, ϱ fields. We compare the predictions of our model with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coefficients of the theory. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we show that our approach represents a natural modelling of nuclear matter under the extreme conditions of density as the ones found in the interior of neutron stars. Moreover, we show that naturalness play a major role in effective field theory and, in combination with experiment, could represent a relevant criterium to select a model among others in the description of global static properties of neutron stars.

We estimate in this work the contribution of the nucleon weak magnetism on the neutrino absorption mean free path inside high density nuclear matter. Our main contribution to this subject involves basically, in the mean field approach, three different ingredients: (a) a relativistic generalization of the approach developed by Sanjay and collaborators; (b) the inclusion of the nucleon weak-magnetism; (c) the inclusion of the pseudo-scalar interaction involving the nucleons. Our preliminary results indicate the consistency of our approach. The novel results we have obtained, considering similar physical conditions as the ones assumed by Sanjay and collaborators, is that the neutrino absorption mean free path is three times the corresponding result obtained by those authors.

We study dense hadronic matter in a generalized relativistic mean field approach which contains nonlinear couplings of the σ, ω, ϱ, δ fields and compare its predictions for properties of neutron stars with the corresponding results from different models found in the literature. Our predictions indicate a substantial modification in static global properties of nuclear matter and neutron stars with the inclusion of the δ meson into the formalism.

For the nuclear many body problem at high densities, formulated in the framework of a relativistic mean-field theory, we investigate in detail the compression modulus of nuclear matter as a function of the effective nucleon mass. We include consistently in our modelling chemical equilibrium as well as baryon number and electric charge conservation and investigate properties of neutron stars. Among other predictions we focus on the dependence of the maximum mass of a sequence of neutron stars as a function of the compression modulus and the nucleon effective mass.

On the basis of a chiral symmetry transformation, we predict an isovector component for the family of light scalar mesons, i.e. partners of the σ-meson. Such a contribution may be necessary to tune the equation of state of nuclear matter in order to comply with severe constraints from a recent analysis of observational macroscopic properties of neutron stars.

In this work, we calculate the moment of inertia of the pulsar of the binary system J0737-3039A in the framework of Einstein's gravitational theory combined with a relativistic field theoretical approach for nuclear matter in the slow rotating regime, taking into account that the star's frequency is much smaller than Kepler's frequency. In the description of the EoS for nuclear matter, we consider a generalized class of relativistic multi-baryon Lagrangian density mean field approach which contains adjustable nonlinear couplings of the meson fields with the baryon fields. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we determine the EoS of the pulsars. By analyzing the results, dynamical constraints for neutron star models are identified.

We investigate the properties of β-equilibrated electrically charged neutral strange matter and strange stars at finite temperature in the framework of Tsallis statistics [C. Tsallis, J. Stat. Phys.52 (1988) 479]. As the main result of our study we find out that a QHD description of nuclear matter combined with Tsallis statistics may open new possibilities for nuclear matter models.

In a previous work, we have predicted an isovector component of the light scalar meson sector by using the chiral symmetry transformation formalism. On the basis of this result, we study dense hadronic matter in a generalized relativistic mean field approach with σ, ω and ρ mesons as well as nonlinear self-couplings of the I = 1 component of a light scalar meson field and compare its predictions for neutron star properties and with results from different models for nuclear matter found in the literature.

The next generation of gravitational wave observatories are promissing candidates to make the first detections. Once the detection occurs the GW characteristics permit to extract some information about the gravitational wave source. In the present work we focus on waves produced by neutron stars which can give stringent constraints on the nuclear matter equation of state. The microscopic description is based on a nonlinear field-theoretical model in order to construct such an equation of state. The model has free parameters, which from actual knowledge may not be pinned down by direct nuclear matter experiments. An important example is the hyperon-sigma meson coupling constant, currently determined by the spin-isospin SU(6) scheme. The coupling constant is of significant relevance for the structure of the equation of state, controlling its rigidity and, consequently, the properties of neutron stars and gravitational wave signals. We show, in this work, how one can constrain the hyperon-sigma meson coupling constant assuming the detection of a gravitational wave.

By considering the expression for the total neutrino luminosity, L_ν, in terms of the neutrino total emissivity and the volume of a neutron star, we confirm that indeed the luminosity for the direct URCA processes has a dependence on temperature of order T⁶ as assumed by Heinke and Ho. However, as can be seen in our formulation, L_ν depends also on a variety of ingredients that characterize properties of dense nuclear matter as baryon effective masses, Fermi momenta and energy, as well as parameters that characterize the weak interaction beta process. In particular, the dependence of the luminosity of neutrinos in the effective mass of baryons that make up a neutron star opens a new perspective on the study of properties of dense nuclear matter. The model adopted in our calculations may represent, we believe, a further step in elucidating the mysteries surrounding the cooling of Cassiopeia A. Work along this line is in progress

We present a relativistic effective model with derivative couplings which includes genuine many-body forces simulated by nonlinear interaction terms involving scalar-isoscalar (σ, σ*), vector-isoscalar (ω, ɸ), vector-isovector (ϱ), scalar-isovector (δ) mesons. The effective model presented in this work has a philosophy quite similar to the original version of the model with parameterized couplings. But unlike that, in which the parametrization is directly inserted in the coupling constants of the Glendenning model, we present here a method for the derivation of the parametric dependence of the coupling terms, in a way that allows in one side to consistently justify this parametrization and in the other to extend in a coherent way the range of possibilities of parameterizations in effective models with derivative couplings. The extended model is then applied to the description of the mass of neutron stars.

In this work we study the effect of the accretion of dark matter into neutron stars. We have considered two relativistic nuclear effective models for the structure of neutron stars (ZM and Boguta-Bodmer) and three profiles for dark matter (Navarro-Frenk-White, Einasto, and Burkert). We have analyzed the effects of these effective models and profiles in the equation of state of nuclear matter and in the capture rate of dark matter by neutron stars. Our results confirm that the capture rate of dark matter by neutron stars is strongly model dependent. This leads to more questions than answers due to the uncertainties in the significance of the results, requiring therefore for its elucidation new signatures of capture of dark matter by these stellar objects.

We study the effects of antikaon condensates in neutron stars in the framework of a relativistic effective model with derivative couplings which includes genuine many-body forces simulated by nonlinear interaction terms involving scalar-isoscalar (σ, σ*), vector-isoscalar (ω, ɸ), vector-isovector (ϱ), scalar-isovector (δ) mesons. The effective model presented in this work has a philosophy quite similar to the original version of the model with parameterized couplings. But unlike that, in which the parametrization is directly inserted in the coupling constants of the Glendenning model, we present here a method for the derivation of the parametric dependence of the coupling terms, in a way that allows in one side to consistently justify this parametrization and in the other to extend in a coherent way the range of possibilities of parameterizations in effective models with derivative couplings. The extended model is then applied to the description of the mass of neutron stars.

We study the effects of phase transition in the equation of state of a neutron star containing a condensate of anti-kaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, and δ meson fields in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase transition to the anti-kaons condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between hadron matter and the condensed of anti-kaons. In conclusion, we have found that isovector meson degrees of freedom contribute to tighten the Equation of State of Neutron Stars.

A recently developed effective relativistic theory for nuclear matter is applied to the description of the cooling process of baryon degenerate neutron star matter through neutrino emission considering direct URCA processes. In our approach nucleons and antikaon condensates interact with σ, ω, ρ, δ and ς meson fields. Our results indicate a substantial decrease of the critical threshold density for the URCA process. This is because the presence of these interacting degrees of freedom increase the proportion of protons, producing simultaneously the reduction of the isospin asymmetry in nuclear matter. Our results also indicate that neutron stars with larger masses than M_NE ~ 0.9M_⊙, which represents the stellar critical threshold (the mass of the neutron star whose baryon central density reached the critical density) would be cooled efficiently and be outside the possibility of observation by heat radiation in a few years.

We investigate relativistic bound states for a hypothetical light scalar gluino pair (gluinonium), in the framework of the covariant Bethe-Salpeter equation (BSE). In this paper, we derive, from the covariant BSE for a fermion-anti-fermion system, using charge conjugation, the corresponding bound-state equation for a gluino pair and we then formulate, for a static harmonic kernel, the coupled differential equations for the corresponding static Bethe-Salpeter amplitude. The steps of our approach then include a numerical solution of the Bethe-Salpeter amplitude for a two-body interaction consisting of scalar, pseudo-scalar, and four-vector components and the determination of the energy spectrum for the ground and the radially excited states of massive gluinonium. We found the energy spectrum and radial distributions of fundamental and excited states of gluinonium. The comparison of the values obtained in the extreme relativistic case with the corresponding values predicted by a harmonic oscillator potential model shows that there is good agreement between the two formulations. The predictions of the binding energy of glunionium in the non-relativistic model are however systematically higher.