Compact stars with 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 dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta-Bodmer-Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B ≥ 10 17 G, in particular the matter properties become anisotropic. Moreover, for the central fields B ≥ 10 18 G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value B cr ≃ 10 19 G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value B cr .

We describe the microphysics, phenomenology, and astrophysical implication of a B-field induced unpairing effect that may occur in magnetars, if the local B-field in the core of a magnetar exceeds a critical value Hc2. Using the Ginzburg-Landau theory of superconductivity, we derive the Hc2 field for proton condensate taking into the correction (≤ 30%) which arises from its coupling to the background neutron condensate. The density dependence of pairing of proton condensate implies that Hc2 is maximal at the crust-core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogenous constant fields will be partially superconducting for "medium-field" magnetars (10 15 ≤ B ≤ 5 × 10 16 G) whereas "strong-field" magnetars (B > 5 × 10 16 G) will be void of superconductivity. The neutrino emissivity of a magnetar's core changes in a twofold manner: (i) the B-field assisted direct Urca process is enhanced by orders of magnitude, because of the unpairing effect in regions where B ≥ Hc2; (ii) the Cooper-pair breaking processes on protons vanish in these regions and the overall emissivity by the pair-breaking processes is reduced by a factor of only a few.

We study the consequences of CPT and lepton number violation in neutrino sector. For CPT violation we take gravity with which neutrino and antineutrino couple differently. Gravity mixes neutrino and antineutrino in an unequal ratio to give two mass eigenstates. Lepton number violation interaction together with CPT violation gives rise to neutrino-antineutrino oscillation. Subsequently, we study the neutrino flavor mixing and oscillation under the influence of gravity. It is found that gravity changes flavor oscillation significantly which influences the relative abundance of different flavors in present universe. We show that the neutrinoless double beta decay rate is modified due to presence of gravity− the origin of CPT violation, as the mass of the flavor state is modified.

We construct an equation of state of strange quark matter in strong magnetic field within a confining model. The confinement is modeled by means of the Richardson potential for quark-quark interaction modified suitably to account for strong magnetic field. We compare our results for the equation of state and magnetization of matter to those derived within the MIT bag model. The differences between these models arise mainly due to the momentum dependence of the strong interaction between quarks in the Richardson model. Specifically, we find that the magnetization of strange quark matter in this model has much more pronounced de Haas-van Alf\'{v}en oscillations than in the MIT bag model, which is the consequence of the (static) gluon-exchange structure of the confining potential.Comment: v3: Published version, a correction in the title; v2: minor changes, version in print, v1: 7 page, 5 figure

Recent results and data suggest that high magnetic fields in neutron stars (NS) strongly affect the characteristics (radius, mass) of the star. Such stars are even separated into a class known as magnetars, for which the surface magnetic field is greater than 1014 G. In this work we discuss the effect of such a high magnetic field on the phase transition of a NS to a quark star (QS). We study the effect of magnetic field on the transition from NS to QS including the magnetic‐field effect in the equation of state (EoS). The inclusion of the magnetic field increases the range of baryon number densities for which the flow velocities of the matter in the respective phase are finite. The magnetic field helps in initiation of the conversion process. The velocity of the conversion front, however, decreases due to the presence of the magnetic field, as the presence of the magnetic field reduces the effective pressure (P). The magnetic field of the star is decreased by the conversion process, and the resultant QS has lower magnetic field than the initial NS.

Abstract. Surface tension (S ) is due to the inward force experienced by particles at the surface and usually gravitation does not play an important role in this force. But in compact stars the gravitational force on the particles is very large and S is found to depend not only on the interactions in the strange quark matter, but also on the structure of the star, i.e. on its mass and radius. Indeed, it has been claimed recently that 511 keV photons observed by the space probe INTEGRAL from the galactic bulge may be due to e + e − annihilation, and their source may be the positron cloud outside of an antiquark star. Such stars, if they exist, may also go a long way towards explaining away the antibaryon deficit of the universe. For that to happen S must be high enough to allow for survival of quark/antiquark stars born in early stages of the formation of the universe. High value of S may also assist explanation of delayed γ-ray burst after a supernova explosion, as conversion from normal matter to strange matter takes place. The possibility of some implications from formation of surface waves are also discussed.

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Nanocrystalline Mg-Zn ferrite phases obtained by high-energy ball milling a stoichiometric (0:5 : 0:5 : 1) powder mixture of MgO, ZnO, and -Fe 2 O 3 at room temperature are subjected to postannealing treatment to study the stability of nanocrystalline ferrite phases at elevated temperatures. An X-ray diffraction (XRD) study using the Rietveld method of structure refinement reveals that ferrite phases generally decompose by releasing MgO and ZnO from ferrite lattices at 873 K. A nonstoichiometric Zn-ferrite is observed in the unmilled mixture at 973 K without MgO in the ferrite lattice, with a particle size four times (approximately 23 nm) larger than that obtained in the high-energy ball-milled samples (approximately 5 nm) at room temperature. The particle size of the unmilled and ball-milled samples increases rapidly to approximately 350 nm after postannealing at 1473 K and the XRD results agree well with the results of the direct observation of ferrite grains by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM).