Effect of Muons on the Phase Transition in Magnetised Proto-Neutron Star Matter

We study the effect of inclusion of muons and the muon neutrinos on the phase transition from nuclear to quark matter in a magnetised proto-neutron star and compare our results with those obtained by us without the muons. We find that the inclusion of muons changes slightly the nuclear density at which transition occurs.However the dependence of this transition density on various chemical potentials, temperature and the magnetic field remains quantitatively the same.Comment: LaTex2e file with four postscript figure

Color-flavor locked strange matter

We analyze how the CFL states in dense matter work in the direction of enhancing the parameter space for absolutely stable phases (strange matter). We find that the "CFL strange matter" phase can be the true ground state of hadronic matter for a much wider range of the parameters of the model (the gap of the QCD Cooper pairs $\Delta$, the strange quark mass $m_s$ and the Bag Constant $B$) than the state without any pairing, and derive a full equation of state and an accurate analytic approximation to the lowest order in $\Delta$ and $m_{s}$ which may be directly used for applications. The effects of pairing on the equation of state are found to be small (as previously expected) but not negligible and may be relevant for astrophysics.Comment: 5 pages, 2 figure

Asymmetric core combustion in neutron stars and a potential mechanism for gamma ray bursts

We study the transition of nuclear matter to strange quark matter (SQM) inside neutron stars (NSs). It is shown that the influence of the magnetic field expected to be present in NS interiors has a dramatic effect on the propagation of a laminar deflagration (widely studied so far), generating a strong acceleration of the flame in the polar direction. This results in a strong asymmetry in the geometry of the just formed core of hot SQM which resembles a cylinder orientated in the direction of the magnetic poles of the NS. This geometrical asymmetry gives rise to a bipolar emission of the thermal neutrino-antineutrino pairs produced in the process of SQM formation. The neutrino-antineutrino pairs annihilate into electron-positron pairs just above the polar caps of the NS giving rise to a relativistic fireball, thus providing a suitable form of energy transport and conversion to gamma emission that may be associated to short gamma ray bursts (GRBs).Comment: 2 figure

Strange Stars with a Density-Dependent Bag Parameter

We have studied strange quark stars in the framework of the MIT bag model, allowing the bag parameter B to depend on the density of the medium. We have also studied the effect of Cooper pairing among quarks, on the stellar structure. Comparison of these two effects shows that the former is generally more significant. We studied the resulting equation of state of the quark matter, stellar mass-radius relation, mass-central-density relation, radius-central-density relation, and the variation of the density as a function of the distance from the centre of the star. We found that the density-dependent B allows stars with larger masses and radii, due to stiffening of the equation of state. Interestingly, certain stellar configurations are found to be possible only if B depends on the density. We have also studied the effect of variation of the superconducting gap parameter on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in Phys. Rev. (D

Quark mass effects on the stability of hybrid stars

We perform a study of the possible existence of hybrid stars with color superconducting quark cores using a specific hadronic model in a combination with an NJL-type quark model. It is shown that the constituent mass of the non-strange quarks in vacuum is a very important parameter that controls the beginning of the hadron-quark phase transition. At relatively small values of the mass, the first quark phase that appears is the two-flavor color superconducting (2SC) phase which, at larger densities, is replaced by the color-flavor locked (CFL) phase. At large values of the mass, on the other hand, the phase transition goes from the hadronic phase directly into the CFL phase avoiding the 2SC phase. It appears, however, that the only stable hybrid stars obtained are those with the 2SC quark cores.Comment: 12 pages, 7 eps figures; v2: figures and table modified after correction of a minor numerical mistake, discussion clarified, references added, conclusions unchanged; version to appear in PL

Effects of color superconductivity on the structure and formation of compact stars

We show that if color superconducting quark matter forms in hybrid or quark stars it is possible to satisfy most of recent observational boundaries on masses and radii of compact stellar objects. An energy of the order of $10^{53}$ erg is released in the conversion from a (metastable) hadronic star into a (stable) hybrid or quark star in presence of a color superconducting phase. If the conversion occurs immediately after the deleptonization of the proto-neutron star, the released energy can help Supernovae to explode. If the conversion is delayed the energy released can power a Gamma Ray Burst. A delay between the Supernova and the subsequent Gamma Ray Burst is possible, in agreement with the delay proposed in recent analysis of astrophysical data.Comment: 4 pages, 2 figures. To be published in Phys.Rev.

The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model

We investigate the structure of hybrid stars based on two different constructions: one is based on the Gibbs condition for phase coexistence and considers the existence of a mixed phase (MP), and the other is based on the Maxwell construction and no mixed phase is obtained. The hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained are model dependent but not significantly different for both constructions.Comment: 8 pages, 7 figures, 3 table

Особливості розв’язку задач параметричної ідентифікації динамічних систем в умовах інтервальної невизначеності

Розглянуто задачу параметричної ідентифікації лінійних динамічних систем методами аналізу інтервальних даних. Показано, що у випадку врахування початкових інтервальних наближень дискретних значень прогнозованої характеристики дана задача є задачею розв’язування інтервальної системи нелінійних алгебричних рівнянь. Досліджено особливості формування та властивості розв’язку таких систем.Рассмотрена задача параметрической идентификации линейных динамических систем методами анализа интервальных данных. Показано, что в случае учета начальных интервальных приближений дискретных значений прогнозированной характеристики, данная задача есть задачей решения интервальной системы нелинейных алгебраических уравнений; исследованы особенности формирования и свойства решения таких систем.The problem of parameter identification of linear dynamic systems by methods of analysis of interval data is considered. It is shown that in the case of taking into account the initial interval approximations of discrete values of the predicted characteristics, this problem is the problem of solving interval system of nonlinear algebraic equations