In this paper, we calculate some of the polarized neutron matter properties, using the lowest order constrained variational method with the AV 18 potential and * Corresponding author † E-mail : bordbar@physics.susc.ac.ir ‡ Permanent address 1 employing a microscopic point of view. A comparison is also made between our results and those of other many-body techniques. 21.65.+f, 26.60.+c, 64.70.-p IntroductionPulsars are rapidly rotating neutron stars with strong surface magnetic fields in the range of 10 12 − 10 13 Gauss [1, 2, 3]. The physical origin of this magnetic field remains an open problem and there is still no general consensus regarding the mechanism to generate such strong magnetic fields in a neutron star. There exist several possibilities of the generation of the magnetic field in a neutron star, from the nuclear physics point of view, however, one of the most interesting and stimulating mechanisms which have been suggested is the possible existence of a phase transition to a ferromagnetic state at densities corresponding to the theoretically stable neutron stars and, therefore, of a ferromagnetic core in the liquid interior of such compact objects. Such a possibility has been studied by several authors using different theoretical approaches , but the results are still contradictory.Whereas some calculations, like for instance the ones based on Skyrmelike interactions predict the transition to occur at densities in the range (1 − 4)ρ 0 (ρ 0 = 0.16f m −3 ), others, like recent Monte Carlo [20] and Brueckner-Hartree-Fock calculations [21-23] using modern two-and three-body realistic interactions exclude such a transition, at least up to densities around five times ρ 0 . This transition could have important consequences for the evolution of a protoneutron star, in particular for the spin correlations in the medium which do

In this paper, we calculate properties of the spin polarized asymmetrical nuclear matter and neutron star matter, using the lowest order constrained variational (LOCV) method with the AV 18 , Reid93, U V 14 and AV 14 potentials. According to our results, the spontaneous phase transition to a ferromagnetic state in the asymmetrical nuclear matter as well as neutron star matter do not occur.

In this paper we study the magnetic susceptibility and other thermodynamic properties of the polarized nuclear matter at finite temperature using the lowest order constrained variational (LOCV) method employing the AV 18 potential. Our results show a monotonic behavior for the magnetic susceptibility which indicates that the spontaneous transition to the ferromagnetic phase does not occur for this system. *

The equation of state of de-confined quark matter within the MIT bag model is calculated. This equation of state is used to compute the structure of a neutron star with quark core. It is found that the limiting mass of the neutron star is affected considerably by this modification of the equation of state. Calculations are carried out for different choices of the bag constant.

Some properties of the polarized neutron matter at finite temperature has been studied using the lowest order constrained variational (LOCV) method with the AV 18 potential. Our results indicate that spontaneous transition to the ferromagnetic phase does not occur. Effective mass, free energy, magnetic susceptibility, entropy and the equation of state of the polarized neutron matter at finite temperature are also calculated. A comparison is also made between our results and those of other many-body techniques.

The lowest order constrained variational method is applied to calculate the polarized symmetrical nuclear matter properties with the modern AV 18 potential performing microscopic calculations. Results based on the consideration of magnetic properties show no sign of phase transition to a ferromagnetic phase.

In this paper we study the possibility of spontaneous ferromagnetic and antiferromagnetic phase transitions of asymmetrical nuclear matter using the lowest-order constrained variational technique with AV 18 potential and employing a microscopic point of view. Our results show that the spontaneous transition to ferromagnetic and antiferromagnetic phases cannot occur for asymmetric nuclear matter.

In this paper, we have calculated the equation of state of asymmetric nuclear matter using the lowest order constrained variational approach and Argonne family potentials with and without three-nucleon interaction(TNI) contribution. In particular, we have used the AV18 potential and the re-projected potentials, AV8′, and AV6′. We have also calculated the saturation properties of symmetric nuclear matter, and the nuclear symmetry energy using AV18 +TNI, AV8′+TNI and AV6′+TNI potentials. The inclusion of TNI has modified the agreement with experiment. We have also made a comparison between our results and those of other many-body calculations.