Bardo E. J. Bodmann

CONSTRAINTS ON THE HYPERON-SIGMA MESON COUPLING BY GW OBSERVATIONS

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.

ON THE CONFINED–DECONFINED PHASE TRANSITION IN NUCLEAR MATTER AND NEUTRON STARS

In this work we focus our study on the transition from hadron to deconfined quark matter, and we shall assume that the phase transition is first-order with two independent components, which are related to the local conservation of baryon number and the global conservation of electric charge. Relativistic effective theories are employed to describe the hadron and quark phase. Two different hadronic models are adopted: an adjustable model and the well known Boguta–Bodmer model. Deconfined phase is described employing the MIT bag model. Previous studies showed that the choice of the hadronic model as well as its parameters (including nucleon effective mass and hyperonic coupling schemes) have influence on phase transition properties. Our aim is to analyze if such results on phase transition play an important role on the modeling of neutron stars. To carry out such analysis, the Tolman–Oppenheimer–Volkoff equations are employed to determine the maximum mass for each combination of hadronic model and parameters.

STABILITY OF NEUTRON STARS WITH LARGE AMOUNT OF STRANGENESS AND THE ROLE OF δ-MESON

We investigate the role of the strange σ*, ϕ and δ meson fields on the delineation of main properties of neutron stars using a parameterized Lagrangian density model in the effective baryon and meson sectors. We assume, strange quarks are localized within the hyperon fields, which carry the strangeness content of the model. Our main goal is to analyze stability conditions of neutron stars with large amount of strangeness per baryon. Our main result indicates the inclusion of the strange (anti-)quark containing meson field σ*, besides ϕ and δ into nuclear matter, turn the equation of state stiffer this way increasing the gravitational mass of the neutron star.

ISOVECTOR COMPONENTS OF LIGHT SCALAR MESON AND NUCLEAR MATTER PROPERTIES

We have predicted (contribution to this issue) 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 with results from different models for nuclear matter found in the literature.

ANALYZING HADRON-QUARK MATTER PHASE TRANSITION BY MACROSCOPIC PROPERTIES OF NEUTRON STARS

A complementary way to investigate the Hadron-Quark-Gluon Phase transition in heavy ion collisions is to analyze properties of dense astrophysical objects, i.e. neutron stars. A neutron star can be simply described as a giant nucleus. However, due to the enormous gravitational contraction, it can reach densities up to several times the density found in the Pb nucleus. This property allows the formation of a core made up of free quarks and gluons. Once this new phase is formed, the new state drastically changes the neutron star macroscopic properties, such as its mass and radius. In the present work, we follow a route opposite to the common sense, investigating the properties of the phase transition by analyzing neutron star properties of mass and radius. This observations can determine the density where the transition can occur or the order of the transition using some sort of reverse engineering. As a consequence, the values of the bag constant or the strong coupling constant can be inferred.

ISOVECTOR COMPONENTS OF THE SCALAR σ-MESON FAMILY AS NEW INGREDIENTS FOR NUCLEAR MATTER MODELS

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.

ON THE ROLE OF THE ADIABATIC INDEX IN THE STABILITY OF NEUTRON STARS

We study the influence of interaction strengths on nuclear properties and global static properties of neutron stars with emphasis on the adiabatic index, considering also the constraint of chemical equilibrium and charge neutrality. We develop an equation of state (EoS) in the framework of an extended effective QHD model using a parameterized phenomenological Lagrangian density containing the fundamental baryon octet, the σ, ω and ϱ meson fields and the lightest charged leptons. The results of our approach show that, for a small range of values of the baryon–meson coupling parameters, we can consistently describe nuclear matter and the structure of neutron stars. Our results indicate that in the energy density range above hyperon thresholds, the behavior of the adiabatic index is roughly comparable to the corresponding one in the case of an extreme relativistic hydrodynamical perfect fluid.

A FINITE TEMPERATURE RELATIVISTIC NUCLEAR MODEL FOR NEUTRON STARS IN A SLOW ROTATIONAL SCENARIO

We study the effects of temperature in hadron dense matter within a generalized relativistic mean field approach based on the naturalness of the coupling constants of the theory. The Lagrangian density of our formulation contains nonlinear self-couplings of the σ meson field coupled to baryons and to the ω and ϱ meson fields. Moreover, we use the Sommerfeld and Hartle approximations to extend our approach to the finite temperature domain and slow rotational scenario. Both Sommerfeld and Hartle approximation allows a drastic simplification of computational work while improving the capability of theoretical analysis of the role of temperature and rotation on properties of protoneutron stars. Our predictions indicate that in the slow rotating regimen, neutron stars density profiles as well as the maximum mass and the inertial moment of these stellar objects are well approximated by the zero temperature approximation.

STABILITY OF NEUTRON STARS WITH A LARGE AMOUNT OF STRANGENESS

We investigate the role of the strange σ* and ϕ meson fields on the delineation of the main properties of neutron stars using a parameterized Lagrangian density model in the effective baryon and meson sectors. We assume strange quarks are localized within the hyperon fields which carry the strangeness content of the model. Our main goal is to analyze stability conditions of neutron stars with a large amount of strangeness per baryon. Our main result indicates the inclusion of the strange meson fields σ* and ϕ into nuclear matter make the equation of state stiffer thereby increasing the gravitational mass of the neutron star.

STRANGE MATTER AND STRANGE STARS WITH TSALLIS STATISTICS

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.