Macroscopic effects in cold magnetized nucleons and electrons with anomalous magnetic moments

Abstract

A model of a degenerate neutron gas in chemical equilibrium with a background of degenerate electrons and protons in a constant uniform ultrastrong magnetic field is applied to describe the state of matter in the cores of strongly magnetized neutron stars. Expressions for the thermodynamic quantities are obtained including the anomalous magnetic moments of the fermions. It is shown that ͑1͒ the inclusion of the anomalous magnetic moments of charged fermions leads to nonperiodic magnetic oscillations of their thermodynamic quantities in strong magnetic fields, ͑2͒ the total stress energy tensor relevant for neutron star structure must include contributions from both the magnetized matter and the magnetic field and as a result the total pressure produced is anisotropic, and ͑3͒ complete spin polarization of neutrons occurring in superstrong magnetic fields must lead to an increase in the degeneracy pressure compared with the zero field case at the same neutron densities. It is hoped that the results obtained will have applications for the structure in neutron stars with ultrastrong frozen-in magnetic fields.Study of a relativistic electron gas in a strong magnetic field was stimulated by the discovery of magnetic fields of the order of Bу10 13 G at the neutron star surface ͓1-3͔. Such a magnetic field ''frozen in'' a neutron star may become much stronger in its central domain. Gravitational collapse of macroscopic magnetized bodies, composed of neutrons in a strong magnetic field B, may lead to extremely magnetized neutron stars, or magnetars ͓4,5͔. Their magnetic fields at the star surface are estimated to be of the order of Bу10 15 G ͓6,7͔ and the magnetic induction at the star core may go up to 10 18 G ͓8͔. The magnetic induction B needed to affect neutron star structure directly was estimated in ͓9͔ to be Bϳ2ϫ10 18 (M /1.4M ᭪ )(R/10 km) Ϫ2 G, where M and R are, respectively, the neutron star mass and radius.Recently, many works have been concerned with the effect of strong magnetic fields on elementary processes occurring at the star core. The behavior of a relativistic nucleon and electron gas in a constant strong magnetic field was studied in ͓10͔. The equation of state and the magnetization of relativistic fermions in strong uniform magnetic fields including the anomalous magnetic moments of the fermions were partly discussed in ͓11-14͔. The effect of strong magnetic fields on dense neutron-star matter was studied in ͓15,16͔ in the mean field approximation. However, contributions from the magnetic field energy density and pressure were not included ͓15,16͔ while the anisotropic effect of uniform magnetic fields either was not given enough attention ͓11,12͔ or was considered incorrectly ͓13,14͔.As is known ͓17,18͔ the chemical equilibrium in a degenerate gas of neutrons ͑n͒, protons ͑p͒, and electrons ͑e͒ must take into account the direct URCA processes pϩe→nϩ, n→pϩeϩ ͑ and denote the neutrino and antineutrino, respectively͒ in which the total number of baryons n b ϭn p ϩn n is conserved and the electroneutra...

Neutron star matter in the quark-meson coupling model in strong magnetic fields

“…Recent observations of soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) have suggested that the surface magnetic field of young neutron stars could be of order 10 14 − 10 15 G [1]. On the other hand, it is estimated that the interior field in neutron stars may be as large as 10 18 G [2,3].…”

“…On the other hand, it is estimated that the interior field in neutron stars may be as large as 10 18 G [2,3]. Motivated by the existence of strong magnetic fields in neutron stars, theoretical studies on the effect of extremely large fields on dense matter and neutron stars have been carried out by many authors [3,4,5,6,7,8,9,10].…”

Anomalous Electromagnetic Transport in Compact Stars

“…The fact that strong magnetic fields populate the vast majority of the astrophysical compact objects and that they can significantly affect several properties of the star have served as motivation for many works focused on the study of the EoS of magnetized neutron stars, without considering , or considering the magnetic-field interaction with the particle anomalous-magnetic-moment [88,[99][100][101][102][103][104][105][106][107][108][109][110][111][112][113]. An important characteristic is that the EoS in a uniform magnetic field becomes anisotropic, with different pressures along the field and transverse to it [73,94,98].…”

Magnetism in Dense Quark Matter

“…Hence, when investigating the field effects in the EoS, it is consistent to take a magnetic field that is locally constant and uniform. This is the reason why such an approximation has been systematically used in all the previous works on magnetized nuclear [1,20,25,28,29,34,35,72,79,87,115,121,124,136,140,143] and quark matter [32,33,74,104,105,120].…”