310 research outputs found
Spin polarized states in neutron matter at a strong magnetic field
Spin polarized states in neutron matter at a strong magnetic field are
considered in the model with the Skyrme effective interaction (SLy4, SLy7
parametrizations). Analyzing the self-consistent equations at zero temperature,
it is shown that a thermodynamically stable branch of solutions for the spin
polarization parameter as a function of density corresponds to the negative
spin polarization when the majority of neutron spins are oriented oppositely to
the direction of the magnetic field. Besides, beginning from some threshold
density being dependent on the magnetic field strength the self-consistent
equations have also two other branches (upper and lower) of solutions for the
spin polarization parameter with the positive spin polarization.
The free energy corresponding to the upper branch turns out to be very close
to the free energy corresponding to the thermodynamically preferable branch
with the negative spin polarization. As a consequence, at a strong magnetic
field, the state with the positive spin polarization can be realized as a
metastable state at the high density region in neutron matter which under
decreasing density at some threshold density changes into a thermodynamically
stable state with the negative spin polarization. The calculations of the
neutron spin polarization parameter and energy per neutron as functions of the
magnetic field strength show that the influence of the magnetic field remains
small at the field strengths up to G.Comment: Prepared with RevTeX4, 8pp., 5 figs; v.2: matches published versio
Spin ordered phase transitions in neutron matter under the presence of a strong magnetic field
In dense neutron matter under the presence of a strong magnetic field,
considered in the model with the Skyrme effective interaction, there are
possible two types of spin ordered states. In one of them the majority of
neutron spins are aligned opposite to magnetic field (thermodynamically
preferable state), and in other one the majority of spins are aligned along the
field (metastable state). The equation of state, incompressibility modulus and
velocity of sound are determined in each case with the aim to find the
peculiarities allowing to distinguish between two spin ordered phases.Comment: Report at IX HEP Conference, Kharkov, Ukraine, February 21 - 25, 201
Finite temperature effects on spin polarization of neutron matter in a strong magnetic field
Spin polarization of neutron matter at finite temperatures and strong
magnetic fields up to G is studied in the model with the Skyrme
effective interaction. It is shown that, together with the thermodynamically
stable branch of solutions for the spin polarization parameter corresponding to
the case when the majority of neutron spins are oriented opposite to the
direction of the magnetic field (negative spin polarization), the
self-consistent equations, beginning from some threshold density, have also two
other branches of solutions corresponding to positive spin polarization. The
influence of finite temperatures on spin polarization remains moderate in the
Skyrme model up to temperatures relevant for protoneutron stars, and, in
particular, the scenario with the metastable state characterized by positive
spin polarization, considered at zero temperature in Phys. Rev. C {\bf 80},
065801 (2009), is preserved at finite temperatures as well. It is shown that
above certain density the entropy for various branches of spin polarization in
neutron matter with the Skyrme interaction in a strong magnetic field
demonstrates the unusual behavior being larger than that of the nonpolarized
state. By providing the corresponding low-temperature analysis, it is clarified
that this unexpected behavior should be addressed to the dependence of the
entropy of a spin polarized state on the effective masses of neutrons with spin
up and spin down, and to a certain constraint on them which is violated in the
respective density range.Comment: Prepared with RevTeX4, 6pp., 4 figs; v2: accepted in JKA
Finite temperature effects in antiferromagnetism of nuclear matter
The influence of the finite temperature on the antiferromagnetic (AFM) spin
ordering in symmetric nuclear matter with the effective Gogny interaction is
studied within the framework of a Fermi liquid formalism. It is shown that the
AFM spin polarization parameter of partially polarized nuclear matter for low
enough temperatures increases with temperature. The entropy of the AFM spin
state for some temperature range is larger than the entropy of the normal
state. Nerveless, the free energy of the AFM spin state is always less than the
free energy of the normal state and, hence, the AFM spin polarized state is
preferable for all temperatures below the critical temperature.Comment: To appear in PRC; some references and comments adde
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