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Medium effects of magnetic moments of baryons on neutron stars under strong magnetic fields

Physical Review C, 2010

We investigate medium effects due to density-dependent magnetic moments of baryons on neutron stars under strong magnetic fields. If we allow the variation of anomalous magnetic moments (AMMs) of baryons in dense matter under strong magnetic fields, AMMs of nucleons are enhanced to be larger than those of hyperons. The enhancement naturally affects the chemical potentials of baryons to be large and leads to the increase of a proton fraction. Consequently, it causes the suppression of hyperons, resulting in the stiffness of the equation of state. Under the presumed strong magnetic fields, we evaluate relevant particles' population, the equation of state and the maximum masses of neutron stars by including density-dependent AMMs and compare them with those obtained from AMMs in free space.

Stellar matter with a strong magnetic field within density-dependent relativistic models

Journal of Physics G: Nuclear and Particle Physics, 2008

The effect of strong magnetic fields on the equation of state (EoS) for compact stars described with density dependent relativistic hadronic models is studied. A comparison with other mean-field relativistic models is done. It is shown that the largest differences between models occur for low densities and that the magnetic field affects the crust properties of star, namely its extension.

Dense matter in strong magnetic fields

Journal of Physics: Conference Series, 2014

Compact stars having strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10 14 − 10 15 G, the implied internal field strength being several orders larger. We study the equation of state and composition of hypernuclear matter and quark matter-two forms of dense matter in strong magnetic fields. We find that the magnetic field has substantial influence on the properties of hypernuclear matter and quark matter for magnetic field B ≥ 10 17 G and B ≥ 10 18 G respectively. In particular the matter properties become anisotropic. Moreover, above a critical field Bcr, both hypernuclear and quark matter show instability, although the values of Bcr are different for two kinds of matter.

Warm and dense stellar matter under strong magnetic fields

Physical Review C, 2011

We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino free and neutrino trapped matter at a fixed entropy per baryon are analyzed. A relativistic meanfield nuclear model, including the possibility of hyperon formation, is considered. A density dependent magnetic field with the magnitude 10 15 G at the surface and not more than 3 × 10 18 G at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that an hybrid protoneutron star will not evolve to a low mass blackhole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low mass blackhole.

Effects of anisotropy on strongly magnetized neutron and strange quark stars in general relativity

2021

We investigate the properties of anisotropic, spherically symmetric compact stars, especially neutron stars and strange quark stars, made of strongly magnetized matter. The neutron stars are described by SLy equation of state, the strange quark stars by an equation of state based on the MIT Bag model. The stellar models are based on an a priori assumed density dependence of the magnetic field and thus anisotropy. Our study shows that not only the presence of a strong magnetic field and anisotropy, but also the orientation of the magnetic field itself, have an important influence on the physical properties of stars. Two possible magnetic field orientations are considered, a radial orientation, where the local magnetic fields point in the radial direction, and a transverse orientation, where the local magnetic fields are perpendicular to the radial direction. Interestingly, we find that for a transverse orientation of the magnetic field, the stars become more massive with increasing a...

Magnetic Moment of Heavy Baryons

INTERNATIONAL JOURNAL OF ADVANCED SCIENTIFIC AND TECHNICAL RESEARCH, 2017

The baryon magnetic moment is a fundamental observable as its masswhich encodes information of the underlying quark-gluon structure and dynamics. Assuminga conventional correlated perturbative chiral quark model (CPχQM) we suggest that the charmedheavy baryons are a bound state of two light diquarks and a single heavy charm antiquark, the spatially wave function of these diquarks has a P-wave and an S-wave in angular momentum in the first and second version of our model respectively, as the result of these considerations we construct the orbital-flavor-spin symmetry of contribution of quarks. Then we calculate their magnetic moments in our model.

Magnetic moments of the ground-state baryons

Physical Review D, 1983

Baryon magnetic moments are calculated in the harmonic-oscillator quark model incorporating (i) unlike previous attempts, a natural mass scale for quarks, taken as one-third of the nucleon mass for u and d quarks and the strange-quark mass suggested by Lipkin's sum rule m,m"=m~-m~, (ii) a minimal nontrivial mixing,~8-) =cosQ~(56,0+)~o)+sin(t~(70,0+)~2), and (iii) replacement of Pauli spinors by Dirac spinors for including relativistic corrections. In the parameter-free nonrelativistic limit, we find a fairly good fit, which gets further improved in the relativistic case.

Magnetism in Dense Quark Matter

Strongly Interacting Matter in Magnetic Fields, 2013

We review the mechanisms via which an external magnetic field can affect the ground state of cold and dense quark matter. In the absence of a magnetic field, at asymptotically high densities, cold quark matter is in the Color-Flavor-Locked (CFL) phase of color superconductivity characterized by three scales: the superconducting gap, the gluon Meissner mass, and the baryonic chemical potential. When an applied magnetic field becomes comparable with each of these scales, new phases and/or condensates may emerge. They include the magnetic CFL (MCFL) phase that becomes relevant for fields of the order of the gap scale; the paramagnetic CFL, important when the field is of the order of the Meissner mass, and a spin-one condensate associated to the magnetic moment of the Cooper pairs, significant at fields of the order of the chemical potential. We discuss the equation of state (EoS) of MCFL matter for a large range of field values and consider possible applications of the magnetic effects on dense quark matter to the astrophysics of compact stars.

Influence of strong magnetic field on the structure properties of strange quark stars

The European Physical Journal A

We investigate the thermodynamic properties of strange quark matter under the strong magnetic field in the framework of the MIT bag model in two cases of bag constants. We consider two cases of the magnetic field, the uniform magnetic field and the density-dependent magnetic field to calculate the equation of state of strange quark matter. For the case of density-dependent magnetic field, we use a Gaussian equation with two free parameters β and θ and use two different sets of the parameters for the magnetic field changes (a slow and a fast decrease of the magnetic field from the center to the surface). Our results show that the energy conditions based on the limitation of the energy-momentum tensor, are satisfied in the corresponding conditions. We also show that the equation of state of strange quark matter becomes stiffer by increasing the magnetic field. In this paper, we also calculate the structure parameters of a pure strange quark star using the equation of state. We investigate the compactification factor (2M/R) and the surface redshift of star in different conditions. The results show that the strange quark star is denser than the neutron star and it is more compact in the presence of the stronger magnetic field. As another result, the compactification factor increases when we use a slow increase of the magnetic field from the surface to the center. Eventually, we compare our results with the observational results for some strange star candidates, and we find that the structure of the strange star candidates is comparable to that of the star in our model.

Hadronic and hybrid stars subject to density-dependent magnetic fields

2014

In the light of the very massive neutron stars recently detected and the new possible constraints for the radii of these compact objects, we revisit some equations of state obtained for hadronic and hybrid stars under the influence of strong magnetic fields. We present our results for hadronic matter taking into account the effects of the inclusion of anomalous magnetic moment. Additionally, the case of hybrid stars under the influence of strong magnetic fields is considered. We study the structure of hybrid stars based on the Maxwell condition (without a mixed phase), where the hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). The mass-radius relation for each case are calculated and discussed. We show that both hadronic and hybrid stars can bear very high masses and radii compatible with the recently observed high mass neutron stars.