119494697
The Dynamic Cosmological Term $\Lambda$: Some Aspects of Phenomenological Models
Choosing a phenomenological model of $\Lambda$, viz. $\Lambda \sim \dot H$, it has been shown that this model of $\Lambda$ is equivalent to other three types of $\Lambda$, $\Lambda \sim (\dot a/a)^2$, $\Lambda \sim \ddot a/a$ and $\Lambda \sim \rho$. Through an indirect approach, it has also been possible to put a limit on the deceleration parameter $q$. It has been shown that if $q$ becomes less than -1, then this model can predict about the presence of phantom energy.
15541573
Tolman–Bayin type static charged fluid spheres in general relativity
In a static spherically symmetric Einstein-Maxwell spacetime the class of astrophysical solution found out by Ray and Das (2002) and Pant and Sah (1979) are revisited here in connection to the phenomenological relationship between the gravitational and electromagnetic fields. It is qualitatively shown that the charged relativistic stars of Tolman (1939) and Bayin (1978) type are of purely electromagnetic origin. The existence of this type of astrophysical solutions is a probable extension of Lorentz’s conjecture that electr on-like extended charged particle possesses only ‘electromagnetic mass’ and no ‘material mas s’.
119265074
Central density dependent anisotropic compact stars
Stars can be treated as a self-gravitating fluid. In this connection, we propose a model for an anisotropic star under the relativistic framework of Krori and Barua (J. Phys. A, Math. Gen. 8:508, 1975) spacetime. It is shown that the solutions are regular and singularity free. The uniqueness of the model is that interior physical properties of the star solely depend on the central density of the matter distribution.
117429531
Periodicity of ~155 days in solar electron fluence
In this paper we have investigated the occurrence rate of high energetic(E>10 MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle 21 (June, 1976 to August, 1986) first time by three different methods to detect periodicities accurately. Power-spectrum analysis confirms a periodicity ~155 days which is in consistent with the result of Chowdhury and Ray (2006), that "Rieger periodicity" was operated throughout the cycle 21 and it is independent on the energy of the electron fluxes.
14301959
Do Solar System Tests Permit Higher Dimensional General Relativity?
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena. As a test we examine four well known solar system effects, viz., (1) Perihelion shift, (2) Bending of light, (3) Gravitational redshift, and (4) Gravitational time delay. It is shown, under a N-dimensional solutions of Schwarzschild type very narrow class of metrics, that the results related to all these physical phenomena are mostly incompatible with the higher dimensional version of general relativity. We compare all these restricted results with the available data in the literature.
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.
14472580
Strange stars and superbursts at near-Eddington mass accretion rates
Careful assessment of four good superburst candidates for GX 17+2 reveals that superburst is possible at near Eddington mass accretion rates. For the other seven stars, where superburst is found, there is the standard model of burning accumulated carbon from normal type I bursts of the accreting stars. However, there is the need for carbon, nitrogen and oxygen mass fraction (Z_{CNO}) which must be larger than Z_{CNO,\odot}, where the latter refers to the standard value found in the sun. Also it is very difficult to incorporate GX 17+2 into the standard picture of superbursts. In case of superbursts from strange stars, arising from broken quark pairs going over to diquarks at the surface of the star, these problems do not arise. Furthermore there is a natural explanation for the large value of ~ 1000 for \alpha which is defined in the literature as the ratio of energy released between normal bursts to the energy released during the normal burst. In the scenario for superbursts in strange stars it may be argued that the relatively smaller value of \alpha of ~ 440 indicates frequent recurrence of superbursts which is reflected in 4U 1636-53.
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.
118685443
Quasi-solvability of Calogero-Sutherland model with Anti-periodic Boundary Condition
The U(1) Calogero-Sutherland Model with anti-periodic boundary condition is studied. This model is obtained by applying a vertical magnetic field perpendicular to the plane of one dimensional ring of particles. The trigonometric form of the Hamiltonian is recast by using a suitable similarity transformation. The transformed Hamiltonian is shown to be integrable by constructing a set of momentum operators which commutes with the Hamiltonian and amongst themselves. The function space of monomials of several variables remains invariant under the action of these operators. The above properties imply the quasi-solvability of the Hamiltonian under consideration.
6715665
ISOSPIN LATTICE GAS MODEL AND NUCLEAR-MATTER PHASE DIAGRAM AND PRESSURE-VOLUME ISOTHERMS
We study a cubic lattice gas model for nuclear matter where each lattice site can be either occupied, by one proton or one neutron, or unoccupied. A nearest-neighbor interaction of the form - ∑ Jijτziτzj is assumed. Our model is an isospin-1 Ising model, with τz= (1, 0, –1) representing respectively (proton, vacancy, neutron). A kinetic-energy term has been included in our model. Under the Bragg-Williams mean-field approximation our model exhibits the existence of a dense phase (liquid-like) and a rare phase (gas-like). The nuclear-matter p−v isotherms given by our model are discussed.
119869500
Lower bounds on the smallest lepton mixing angle
We give minimal values for the smallest lepton mixing parameter |U{sub e3}|, applying 2-loop renormalization group equations in an effective theory approach. This is relevant in scenarios that predict an inverted neutrino mass spectrum with the smallest mass and |U{sub e3}| being zero at tree level, a situation known to be preserved at 1-loop order. At 2-loop, |U{sub e3}| is generated at a level of 10{sup -12}-10{sup -14}. Such small values are of interest in supernova physics. Corresponding limits for the normal mass ordering are several orders of magnitude larger. Our results show that |U{sub e3}| can in general be expected to be nonzero.