Helio T. Coelho

A FINITE NUCLEON EXTENDED VOLUME MODEL FOR NUCLEAR MATTER

We investigate the effects of a finite volume extension for nucleons immersed in nuclear matter. We wish in this way to explore the role played by this non-vanishing (but fixed) volume in shaping nuclear matter properties, in contrast with other models of nuclear physics in which nucleons are treated as point-like particles. We introduce a model characterized by an exclusion volume a la Van der Waals, as well as an effective non-relativistic approximation to model meson-exchange interactions between nucleons. The model is consistent with experimental values of saturation density and binding energy of nuclear matter in the domain of typical densities for neutron stars.

NEW ASPECTS ON GRAVITATIONAL WAVE EMISSION BY NEUTRON STARS

We discuss, in this work, new aspects related to the emission of gravitational waves by neutron stars, which undergo a phase transition, from nuclear to quark matter, in its inner core. Such a phase transition would liberate around 1052–53 erg of energy in the form of gravitational waves which, if detected, may shed some light in the structure of these compact objects and provide new insights on the equation of state of nuclear matter.

A FUZZY BAG MODEL FOR BARYON-DIBARYON PHASE TRANSITION IN NEUTRON STARS

We propose a model for dibaryon stars which takes into account the internal structure of nucleons via a fuzzy bag model. This choice of nuclear model avoids nucleon self-energy divergences as in the MIT model, and also considers a softer bag surface, thus eliminating the disadvantage of an abrupt transition between the interior of the bag and the external medium. We obtain results for the equation of state and for the mass-radius relation for the dibaryon star. Our results indicate a smaller maximum mass for dibaryon stars as compared to neutron stars, mainly due to the relaxation of the interior Fermi pressure in the dibaryon-populated star core.

Naturalness in an Effective Field Theory for Neutron Star Matter

High density hadronic matter is studied in a generalized relativistic multi‐baryon lagrangian density. By comparing the predictions of our model with estimates obtained within a phenomenological naive dimensional analysis based on the naturalness of the coefficients of the theory, we show that naturalness plays 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.