arXiv subjects

R. Negreiros

Publications and source records attributed to R. Negreiros.

27 records · Page 2Linked to original sources

arXiv2012

Quark core impact on hybrid star cooling

In this paper we investigate the thermal evolution of hybrid stars, objects composed of a quark matter core, enveloped by ordinary hadronic matter. Our purpose is to investigate how important are the microscopic properties of the quark core to the thermal evolution of the star. In order to do that we use a simple MIT bag model for the quark core, and a relativistic mean field model for the hadronic envelope. By choosing different values for the microscopic parameters (bag constant, strange quark mass, strong coupling constant) we obtain hybrid stars with different quark core properties. We also consider the possibility of color superconductivity in the quark core. With this simple approach, we have found a set of microscopic parameters that lead to a good agreement with observed cooling neutron stars. Our results can be used to obtain clues regarding the properties of the quark core in hybrid stars, and can be used to refine more sophisticated models for the equation of state of quark matter.

astro-ph.HE↗

arXiv2012

Structure and Cooling of Neutron and Hybrid Stars

The study of neutron stars is a topic of central interest in the investigation of the properties of strongly compressed hadronic matter. Whereas in heavy-ion collisions the fireball, created in the collision zone, contains very hot matter, with varying density depending on the beam energy, neutron stars largely sample the region of cold and dense matter with the exception of the very short time period of the existence of the proto-neutron star. Therefore, neutron star physics, in addition to its general importance in astrophysics, is a crucial complement to heavy-ion physics in the study of strongly interacting matter. In the following, model approaches will be introduced to calculate properties of neutron stars that incorporate baryons and quarks. These approaches are also able to describe the state of matter over a wide range of temperatures and densities, which is essential if one wants to connect and correlate star observables and results from heavy-ion collisions. The effect of exotic particles and quark cores on neutron star properties will be considered. In addition to the gross properties of the stars like their masses and radii their expected inner composition is quite sensitive to the models used. The effect of the composition can be studied through the analysis of the cooling curve of the star. In addition, we consider the effect of rotation, as in this case the particle composition of the star can be modified quite drastically.

astro-ph.SR↗

arXiv2011

Properties and Stability of Hybrid Stars

We discuss the properties of neutron stars and their modifications due to the occurrence of hyperons and quarks in the core of the star. More specifically, we consider the general problem of exotic particles inside compact stars in light of the observed two-solar mass pulsar. In addition, we investigate neutron star cooling and a possible explanation of the recently measured cooling curve of the neutron star in the supernova remnant Cas A.

astro-ph.SR↗

arXiv2011

Dense Matter and Neutron Stars in Parity Doublet Models

We investigate the properties of dense matter and neutron stars. In particular we discuss model calculations based on the parity doublet picture of hadronic chiral symmetry. In this ansatz the onset of chiral symmetry restoration is reflected by the degeneracy of baryons and their parity partners. In this approach we also incorporate quarks as degrees of freedom to be able to study hybrid stars.

nucl-th↗

arXiv2011

Nuclear matter, nuclei, and neutron stars in hadron and quark-hadron models

We develop a unified model of hadrons and quarks. Within this approach we investigate the phase structure of the model as function of temperature and chemical potential. Computing the equation of state of cold matter we determine neutron and hybrid star masses and radii. In an extension of the investigation we consider the cooling behavior of the compact stars and derive a general relation between the star's mass and rotation and its cooling behavior. Finally we study the effect of Delta resonances for star matter, especially with respect to possible solutions of stars with small radii.

nucl-th↗

arXiv2011

QCD in neutron stars and strange stars

This paper provides an overview of the possible role of Quantum Chromo Dynamics (QDC) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than atomic nuclei. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

astro-ph.HE↗

arXiv2007

Neutron Star Interiors and the Equation of State of Superdense Matter

Neutron stars contain matter in one of the densest forms found in the Universe. This feature, together with the unprecedented progress in observational astrophysics, makes such stars superb astrophysical laboratories for a broad range of exciting physical studies. This paper gives an overview of the phases of dense matter predicted to make their appearance in the cores of neutron stars. Particular emphasis is put on the role of strangeness. Net strangeness is carried by hyperons, K-mesons, H-dibaryons, and strange quark matter, and may leave its mark in the masses, radii, moment of inertia, dragging of local inertial frames, cooling behavior, surface composition, and the spin evolution of neutron stars. These observables play a key role for the exploration of the phase diagram of dense nuclear matter at high baryon number density but low temperature, which is not accessible to relativistic heavy ion collision experiments.

astro-ph↗

arXiv2006

Neutron star interiors and the equation of state of ultra-dense matter

There has been much recent progress in our understanding of quark matter, culminating in the discovery that if such matter exists in the cores of neutron stars it ought to be in a color superconducting state. This paper explores the impact of superconducting quark matter on the properties (e.g., masses, radii, surface gravity, photon emission) of compact stars.

astro-ph↗

arXiv2006

Pulsars as Astrophysical Laboratories for Nuclear and Particle Physics

A forefront area of research concerns the exploration of the properties of hadronic matter under extreme conditions of temperature and density, and the determination of the equation of state--the relation between pressure, temperature and density--of such matter. Experimentally, relativistic heavy-ion collision experiments enable physicists to cast a brief glance at hot and ultra-dense matter for times as little as about $10^{-22}$ seconds. Complementary to this, the matter that exists in the cores of neutron stars, observed as radio pulsars, X-ray pulsars, and magnetars, is at low temperatures but compressed permanently to ultra-high densities that may be more than an order of magnitude higher than the density of atomic nuclei. This makes pulsars superb astrophysical laboratories for medium and high-energy nuclear physics, as discussed in this paper.

astro-ph↗