Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field

摘要

Spin-polarized states in dense neutron matter with the recently developed Skyrme effective interaction (BSk20nparametrization) are considered in the magnetic fields H up to 1020 G at finite temperature. In a strong magneticnfield, the total pressure in neutron matter is anisotropic, and the difference between the pressures parallel andnperpendicular to the field direction becomes significant atH >Hth ∼ 1018 G. The longitudinal pressure decreasesnwith the magnetic field and vanishes in the critical field 1018 < Hc u0002 1019 G, resulting in the longitudinalninstability of neutron matter. With increasing temperature, the threshold Hth and critical Hc magnetic fields alsonincrease. The appearance of the longitudinal instability prevents the formation of a fully spin-polarized state innneutron matter and only the states with moderate spin polarization are accessible. The anisotropic equation ofnstate is determined at densities and temperatures relevant to the interiors of magnetars. The entropy of stronglynmagnetized neutron matter turns out to be larger than the entropy of nonpolarized matter. This is caused by somenspecific details in the dependence of the entropy on the effective masses of neutrons with spin up and spin downnin a polarized state.