PROTO-NEUTRON STAR FORMATION WITH DELTA-RESONANCE MATTER AND TRAPPED NEUTRINOS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1541-1544 ◽  
Author(s):  
J. C. T. OLIVEIRA ◽  
A. G. SOUZA ◽  
S. B. DUARTE ◽  
H. RODRIGUES
Keyword(s):  
Neutron Star ◽  
Mean Field ◽  
Field Approximation ◽  
Medium Composition ◽  
Hadronic Matter ◽  
Mean Field Approximation ◽  
Delta Resonance ◽  
Leptonic Sector ◽  
Proto Neutron Star

In the present work we study the equation of state for asymmetric hadronic matter, to be applied in neutron star structure calculation. The delta-rich hadronic stellar matter condensate is studied in the context of mean-field approximation in an extended Walecka's theory version, including the Rarita–Schwinger 3/2-spinor to the hadronic sector. The leptonic sector is also incorporated in beta-equilibrium to the dense stelar medium composition. The role of neutrino trapping for the the formed photo-neutron structure including delta matter in its composition is discussed.

THE ROLE OF ANTIKAON CONDENSATES IN THE ISOSPIN ASYMMETRY OF NEUTRON STARS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1553-1556
Author(s):  
A. MESQUITA ◽  
M. RAZEIRA ◽  
C. A. Z. VASCONCELLOS ◽  
F. FERNÁNDEZ
Keyword(s):  
Phase Transition ◽  
Optical Potential ◽  
Mean Field ◽  
Field Approximation ◽  
Mixed Phase ◽  
Hadronic Matter ◽  
Mean Field Approximation ◽  
Isospin Asymmetry ◽  
Nucleon Matter

We study the effects of the scalar-isovector light mesons on the isospin asymmetry and phase transition of hadronic matter to hadronic matter with a condensate of antikaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, δ, and ς mesons in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase transition to the antikaons condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between nucleon matter and the condensed antikaons. As expected, our results indicate that the scalar-isovector mesons increase the range of the mixed phase–space, they operate for restoring isospin symmetry and they reduce the value of the effective nucleon mass, independently of the depth of the optical potential for antikaons. Also as expected the increase of the depth of optical potential favors the population of antikaons. Our results predict the density threshold of birth of the K-antikaons. The most expressive result of our calculation is the abrupt change in the isospin asymmetry due to the presence of the condensate. Moreover, we have found that scalar-isovector mesons increase the fraction of protons and reduced the fraction of neutrons in the system, since these mesons couple with the conserved isovector current of baryons and thus the minimum in the energy of the system corresponds to saturated isospin states (symmetric in isospin). Finally, we have found as expected that these mesons produce the stiffness of the EoS.

Impossibility of Spin Polarized States for Neutron Star/Proto-Neutron Star Matter in β-Equilibrium Condition

2003 ◽  
Vol 18 (19) ◽  
pp. 1297-1302
Author(s):  
Sutapa Ghosh ◽  
Soma Mandal ◽  
Somenath Chakrabarty
Keyword(s):  
Neutron Star ◽  
Equilibrium Condition ◽  
Mean Field ◽  
Transition Process ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Ferromagnetic Transition ◽  
Neutron Star Matter ◽  
Spin Polarized ◽  
Proto Neutron Star

It is shown explicitly that a ferromagnetic transition of neutron star (NS)/proto-neutron star (PNS) matter in the β-equilibrium condition with σ-ω-ρ exchange type of mean field approximation can actually occur if and only if the neutrinos remain trapped within the system, and perhaps it is also necessary for the neutrinos/anti-neutrinos to carry some finite nonzero mass. It is further shown that the electrons also play a significant role in this transition process. It is therefore, very much unlikely that such a transition of spin polarization can really take place in old neutron stars of very low temperature, whereas, the possibility of spontaneous ferromagnetic transition cannot be ruled out in a newly born PNS.

THE ROLE OF ANTIKAON CONDENSATES IN THE EQUATION OF STATE OF NEUTRON STARS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1545-1548 ◽  
Author(s):  
F. FERNÁNDEZ ◽  
A. MESQUITA ◽  
M. RAZEIRA ◽  
C. A. Z. VASCONCELLOS
Keyword(s):  
Neutron Stars ◽  
Electric Charge ◽  
Chemical Potential ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Charge Neutrality ◽  
The Mean ◽  
Nucleon Matter

We study the consequences of the presence of a negative electric charge condensate of antikaons in neutron stars using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω and ϱ mesons, in the presence of electrons and muons, to accomplish electric charge neutrality and beta equilibrium. The phase transition to the antikaon condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between nucleon matter and the antikaon condensate. Assuming neutrino-free matter, we observe a rapid decrease of the electron chemical potential produced by the gradual substitution of electrons by kaons to accomplish electric charge neutrality. The exotic composition of matter in neutron star including antikaon condensation and nucleons can yield a maximum mass of about M ns ~ 1.76 M ⊙.

scholarly journals Hybrid Stars in the Framework of NJL Models

2017 ◽  
Vol 45 ◽  
pp. 1760026 ◽  
Author(s):  
Gustavo A. Contrera ◽  
Milva Orsaria ◽  
I. F. Ranea-Sandoval ◽  
Fridolin Weber
Keyword(s):  
Phase Transition ◽  
Quark Matter ◽  
Mean Field ◽  
Field Approximation ◽  
Hadronic Matter ◽  
High Mass ◽  
Mean Field Approximation ◽  
Soft Phase ◽  
Non Local ◽  
Hybrid Stars

We compute models for the equation of state (EoS) of the matter in the cores of hybrid stars. Hadronic matter is treated in the non-linear relativistic mean-field approximation, and quark matter is modeled by three-flavor local and non-local Nambu−Jona-Lasinio (NJL) models with repulsive vector interactions. The transition from hadronic to quark matter is constructed by considering either a soft phase transition (Gibbs construction) or a sharp phase transition (Maxwell construction). We find that high-mass neutron stars with masses up to [Formula: see text] may contain a mixed phase with hadrons and quarks in their cores, if global charge conservation is imposed via the Gibbs conditions. However, if the Maxwell conditions is considered, the appearance of a pure quark matter core either destabilizes the star immediately (commonly for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (generally for local NJL models).

scholarly journals Fluctuations and phases in baryonic matter

2021 ◽  
Vol 57 (7) ◽  
Author(s):  
Len Brandes ◽  
Norbert Kaiser ◽  
Wolfram Weise
Keyword(s):  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Test Case ◽  
Baryonic Matter ◽  
Prototype Test ◽  
Group Methods ◽  
Stabilization Effect ◽  
Dynamical Fluctuations

AbstractThe phase structure of baryonic matter is investigated with focus on the role of fluctuations beyond the mean-field approximation. The prototype test case studied is the chiral nucleon-meson model, with added comments on the chiral quark-meson model. Applications to nuclear matter include the liquid-gas phase transition. Extensions to high baryon densities are performed for both nuclear and neutron matter. The role of vacuum fluctuations is systematically explored. It is pointed out that such fluctuations tend to stabilize the hadronic phase characterized by spontaneously broken chiral symmetry, shifting the chiral restoration transition to very high densities. This stabilization effect is shown to be further enhanced by additional dynamical fluctuations treated with functional renormalisation group methods.

THE ROLE OF SCALAR-ISOVECTOR MESONS AND ANTIKAONS IN NEUTRON STARS

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1549-1552 ◽  
Author(s):  
A. MESQUITA ◽  
M. RAZEIRA ◽  
C. A. Z. VASCONCELLOS ◽  
F. FERNÁNDEZ
Keyword(s):  
Phase Transition ◽  
Electric Charge ◽  
Optical Potential ◽  
Chemical Potential ◽  
Mean Field ◽  
Field Approximation ◽  
Hadronic Matter ◽  
Mean Field Approximation ◽  
Charge Neutrality ◽  
Nucleon Matter

We study the effects of the scalar-isovector meson δ and those of a new light scalar-isovector resonance ς on the phase transition of hadronic matter to hadronic matter with a condensate of antikaons, using an effective model with derivative couplings. In our formalism, nucleons interact through the exchange of σ, ω, ϱ, δ, and ς mesons in the presence of electrons and muons to accomplish electric charge neutrality and beta equilibrium. The phase-transition to the antikaon condensate was implemented through the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between nucleon matter and the condensed antikaons. Scalar-isovector mesons operate for restoring isospin symmetry and reduce this way the value of the effective nucleon mass, independent of the depth of the optical potential for antikaons. Moreover, as expected we found that an increase of the depth of optical potential favors the population of antikaons. Finally, assuming neutrino-free matter, we observe a rapid decrease of the electron chemical potential produced by the gradual substitution of electrons by kaons to accomplish electric charge neutrality.

scholarly journals THE INFLUENCE OF THE MAGNETIC FIELD ON THE PROPERTIES OF NEUTRON STAR MATTER

2007 ◽  
Vol 22 (07n10) ◽  
pp. 623-629 ◽  
Author(s):  
WEI CHEN ◽  
PU-QING ZHANG ◽  
LIANG-GANG LIU
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Neutron Star Matter ◽  
Density Region ◽  
High Density Region ◽  
The Difference ◽  
The Magnetic Field

In the mean field approximation of the relativistic σ-ω-ρ model, the magnetic fields are incorporated, and it's influence on the properties of n-p-e neutron star matter are studied. When the strength of the magnetic field is weaker than ~1018G, the particles' fractions and chemical potentials, matter's energy density and pressure hardly change with the magnetic field; when the strength of the magnetic field is stronger than ~1020G, the above quantities change with the magnetic field evidently. Furthermore, the pressure is studied in both thermodynamics and hydrodynamics. The difference between these two ways exits in the high density region, that is, the thermal self-consistency may not be satisfied in this region if the magnetic field is considered.

SEXUAL REPRODUCTION IN A SIMPLE GROWTH POPULATION MODEL

2012 ◽  
Vol 23 (05) ◽  
pp. 1250022
Author(s):  
CARLOS GENTIL ORO LEMOS ◽  
MARCIO SANTOS
Keyword(s):  
Sexual Reproduction ◽  
Mean Field ◽  
Field Approximation ◽  
Reaction Model ◽  
Mean Field Approximation ◽  
Spatial Density ◽  
Simple Growth ◽  
Offspring Generation ◽  
Surface Reaction Model

One of the most important characteristics in the survival of a species is related to the kind of reproduction responsible for the offspring generation. However, only in the last years the role played by sexual reproduction has been investigated. Then, for a better understanding of this kind of process we introduce, in this work, a surface reaction model that describes the role of the sexual reproduction. In our model two different elements of the species, representing male and female, can interact to reproduce a new element. The sex of this new element is chosen with a given probability and in order to take into account the mortality rate we introduce another kind of individual. The value of the spatial density of this element remains constant during the time evolution of the system. The model is studied using Monte Carlo simulations and mean field approximation. Depending on the values of the control parameters of the model, the system can attain two stationary states: In one of them the population survives and in the other it can be extinguished. Besides, accordingly to our results, the phase diagram of the model shows a discontinuous transition between these two states.

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