8136121
Chromo-thermal instabilities and collapse of quark stars to black holes Astrophysical Implications
We have studied the effects of temperature on the properties of strange stars. We find that the maximum mass of the strange star decreases with the increase of temperature, because at high temperatures the equation of states become softer. Moreover, if the temperature of a strange star increases keeping its baryon number fixed, its gravitational mass increases and radius decreases which leads to a limiting temperature where it turns into a black hole. These features of strange stars is a combined effect of change of gluon mass and the quark distribution function with temperature. We have discovered a new kind of radial oscillations of strange stars driven by what we named chromo-thermal instability. This instability and the related radial oscillations of the star is inherent to strange quark matter making strange stars even more exotic than neutron stars within astrophysical context. In particular, we discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma ray bursts. Subject headings: compact object – neutron star – strange star – black hole – GRB – afterglow
583746
Compact strange stars with a medium dependence in gluons at finite temperature
Aims. The possible existence of strange stars in the universe will help in the understanding of various properties of quantum chromodynamics, like asymptotic freedom and chiral symmetry restoration, which is otherwise very difficult to prove in laboratory experiments. Methods. Strange star properties were calculated using large color approximation with built-in chiral symmetry restoration. A relativistic Hartree Fock calculation was performed using the Richardson potential as an interquark interaction. This potential has the asymptotic freedom and a confinement-deconfinement mechanism built into it and the present calculation employs an application of this potential with modified two scale parameters Λ and $\Lambda^{\prime}$, to find a new set of equations of state for strange quark matter. The linear confinement string tension from lattice calculations is 350 MeV and the Coulomb -like part has the parameter 100 MeV from deep inelastic scattering experiments. We also consider the effect of temperature, on gluon mass in a simple way, in addition to the usual density dependence, Results. We obtained a set of new equation of states for strange quark matter and also found that the transition temperature from hadronic matter to strange matter is at 80 MeV, close to the 100 MeV estimated in literature. Conclusions. Formation of strange stars may be the only signal for formation of quark-gluon plasma with asymptotic freedom and chiral symmetry restoration and this may be observable through many processes – such as for example through delayed γ ray afterglow.
10219702
Stability of strange stars (SS) derived from a realistic equation of state.
A realistic EOS (equation of state) leads to strange stars (ReSS) which are compact in the mass–radius (M–R) plot, close to the Schwarzschild limiting line.1 Many of the observed stars fit in with this kind of compactness, irrespective of whether they are X-ray pulsars, bursters or soft γ repeaters or even radio pulsars. We point out that a change in the radius of a star can be small or large, when its mass is increasing and this depends on the position of a particular star on the M–R curve. We carry out a stability analysis against radial oscillations and compare with the EOS of other SS models. We find that the ReSS is stable and an M–R region can be identified to that effect.
119362075
Strange stars at finite temperature
We calculate strange star properties, using large Nc approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock meanfield approximation method, using a modified Richardson potential with two scale parameters Λ and Λ', to find a new set of equation of state (EOS) for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom (AF) and CSM.
119301631
Some simple models for quark stars
We find two new classes of exact solutions for the Einstein-Maxwell equations. The solutions are obtained by considering charged anisotropic matter with a linear equation of state consistent with quark stars. The field equations are integrated by specifying forms for the measure of anisotropy and a gravitational potential which are physically reasonable. The solutions found generalize the Mark-Harko model and the Komathiraj-Maharaj model. A graphical analysis indicates that the matter variables are well behaved.
197508300
CMB power spectrum estimation with non-circular beam and incomplete sky coverage
197509585
Oscillatory Universe, dark energy equation of state and general relativity
The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the frame work of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The `classical' general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy.
119182931
ISOTROPIC CASES OF STATIC CHARGED FLUID SPHERES IN GENERAL RELATIVITY
In this paper we study the isotropic cases of static charged fluid spheres in general relativity. For this purpose we consider two different specializations and under these we solve the Einstein–Maxwell field equations in isotropic coordinates. The analytical solutions thus obtained are matched to the exterior Reissner–Nordstrom solutions which concern the values for the metric coefficients eν and eμ. We derive the pressure, density and pressure-to-density ratio at the center of the charged fluid sphere and boundary R of the star. Our conclusion is that static charged fluid spheres provide a good connection to compact stars.
119114050
Optimization of the baseline and the parent muon energy for a low energy neutrino factory
We discuss the optimal setup for a low energy neutrino factory in order to achieve a 5\sigma-discovery of a nonzero mixing angle \theta_{13}, a nonzero CP phase \delta_{CP}, and the mass hierarchy. We explore parent muon energies in the range 5--16 GeV, and baselines in the range 500--5000 km. We present the results in terms of the reach in sin^2\theta_{13}, emphasizing the dependence of the optimal baseline on the true value of \delta_{CP}. We show that the sensitivity of a given setup typically increases with parent muon energy, reaching saturation for higher energies. The saturation energy is larger for longer baselines; we present an estimate of this dependence. In the light of the recent indications of a large \theta_{13}, we also determine how these preferences would change if indeed a large \theta_{13} is confirmed. In such a case, the baselines ~2500 km (~1500 km) may be expected to lead to hierarchy determination (\delta_{CP} discovery) with the minimum exposure.
119307073
Anisotropic strange star with de Sitter spacetime
Stars can be treated as self-gravitating fluid. Krori and Barua (J. Phys. A., Math. Gen. 8:508, 1975) gave an analytical solution to that kind of fluids. In this connection, we propose a de Sitter model for an anisotropic strange star with the Krori–Barua spacetime. We incorporate the existence of the cosmological constant on a small scale to study the structure of anisotropic strange stars and come to the conclusion that this doping is very well compatible with the well-known physical features of strange stars.
119195269
Static charged fluid in (2 + 1)-dimensions admitting conformal Killing vectors
New solutions for (2 + 1)-dimensional Einstein–Maxwell spacetime are found for a static spherically symmetric charged fluid distribution with the additional condition of allowing conformal Killing vectors (CKV). We discuss physical properties of the fluid parameters. Moreover, it is shown that the model actually represents two structures, namely (i) Gravastar as an alternative of black hole and (ii) Electromagnetic Mass model depending on the nature of the equation of state of the fluid. Here the gravitational mass originates from electromagnetic field alone. The solutions are matched with the exterior region of the Banados–Teitelboim–Zanelli (BTZ) type isotropic static charged black hole as a consequence of junction conditions. We have shown that the central charge density is dependent on the value of M0, the conserved mass of the BTZ black hole. This, in turn, depends on the black hole event horizon which again is related to the Hawking radiation temperature of a BTZ black hole. Thus, one may have a clu...