International Journal of Modern Physics D

Dependences of the X-ray luminosity (L_x) of young single pulsars, due to ejection of relativistic particles, on electric field intensity, rate of rotational energy loss (Ė), magnetic field, period, and some other parameters of neutron stars are discussed. Influence of the magnetic field and effects of some other parameters of neutron stars on the L_x-Ė and the L_x-τ (characteristic time) dependences are considered. Evolutionary factors also play an important role in our considerations. Only the pulsars with L_{2–10 keV}>10³³erg/s have pulsar wind nebula around them. The pulsars from which γ-ray radiation has been observed have low X-ray luminosity in general.

Protoneutron stars are hot and lepton rich objects formed in type II supernovae. It is natural to regard the evolution of these stars as taking place in several stages. This paper describes results of analysis of protoneutron star evolution for models incorporating an strangeness-rich, neutrino opaque matter equation of state. Of special interest in this paper is the comparison of protoneutron star models for two different phases. One characterized by neutrino trapping and by the value of entropy s=1 and the other, formed when neutrinos leak out of the system, described as a hot deleptonized star. The equation of state adequate for the protoneutron star has been constructed. It has been shown that the maximum stable protoneutron star mass is close to 1.44 M_⊙.

A class of relativistic solutions of compact star which is in hydrostatic equilibrium is obtained in higher dimensions assuming a spherically symmetric space–time. The space–time geometry is assumed to be a (D-1)-spheroid immersed in a D-dimensional Euclidean space. It is noted that the parameter a which is the measure of spheroidicity of the space–time plays here an important role in determining the equation of state of the matter content in such a star. One obtains a realistic solution when the parameter a picks up values for D<9 and for space–time dimensions D≥9. It is also observed that the higher dimensional space–time accommodates a more massive compact object for a given size compared to that in the usual four dimensional space–times.

We study particle production of coherently oscillating inflaton in semiclassical theory of gravity by representing inflaton in coherent and squeezed state formalisms. A comparative study of the inflaton in classical gravity with coherent state inflaton in semiclassical gravity is also presented.

A detailed analysis of the Deep River neutron monitor (NM) data for four different phases of solar activity cycle and for four groups of days chosen according to their different geomagnetic conditions is being carried out. It is found that the 60 quiet day (QD) in a year serve a better purpose for investigating the short/long term variation in cosmic ray (CR) intensity. Furthermore, data has been harmonically analysed for the period 1964–95 to investigate the effect of solar poloidal magnetic field (SPMF) orientation in daily variation (diurnal/semi-diurnal) of CR on geomagnetically QD. The phase of the diurnal and semi-diurnal anisotropy vectors on QD has shown a significant shift to early hours when the SPMF in the northern hemisphere (NH) is positive during the periods 1971–79 and 1992–95 as compared to that during the periods 1964–70 and 1981–90 when the SPMF in NH is negative, showing a periodic nature of daily variation in CR intensity with SPMF.

We discuss the spherical collapse of a two fluid system: a string fluid and a null fluid described by a generalized Vaidya metric. This led us to explicitly describe the effect of a string fluid on the established picture of a null fluid collapse (Vaidya collapse). It is found that there is a shrinkage of the initial data space for naked singularities of Vaidya collapse upon taking into account a string fluid. The implications of the results in the context of the cosmic censorship conjecture are discussed.

The general solution of the gravitational field equations for a full causal bulk viscous stiff cosmological fluid, with bulk viscosity coefficient proportional to the energy density to the power 1/4, is obtained in the flat Friedmann–Robertson–Walker geometry. The solution describes a non-inflationary Universe, which starts its evolution from a singular state. The time variation of the scale factor, deceleration parameter, viscous pressure, viscous pressure-thermodynamic pressure ratio, co-moving entropy and Ricci and Kretschmann invariants is considered in detail.

It is shown that collisions between Alfven wave packets and the cascades generated by these collisions in cosmic electromagnetic fields can determine the photon temperature fluctuations for arcminute scales on the last scattering surface.

This is the first of a series of articles showing how 4 dimensionally covariant analytical procedures developed in the context of General Relativity can be usefully adapted for application in a purely Newtonian framework where they provide physical insights (e.g. concerning helicity currents) that are not so easy to obtain by the traditional approach based on a 3+1 spacetime decomposition. After an introductory presentation of the relevant Milne spacetime structure and the associated Cartan connection, the essential principles are illustrated by application to the variational formulation of simple barotropic perfect fluid models. This variational treatment is then extended to conservative multiconstituent self-gravitating fluid models of the more general kind that is needed for treating the effects of superfluidity in neutron stars.

The effect of a slowly rotating mass on a forced harmonic oscillator with two degrees of freedom is studied in the weak field approximation. It is found that according to the general theory of relativity there is a shift in the resonant frequency of the oscillator which depends on the density and rotational frequency of the gravitational source. The proposed shift is quite small under normal physical situations however it is estimated that for compact X-ray sources such as white dwarfs, pulsars and neutron stars the shift is quite appreciable.

We present a Master equation for description of fermions and bosons for special relativities with two invariant scales, , (c and λ_P). We introduce canonically-conjugate variables (χ⁰,χ) to (∊,π) of Judes-Visser. Together, they bring in a formal element of linearity and locality in an otherwise non-linear and non-local theory. Special relativities with two invariant scales provide all corrections, say, to the standard model of the high energy physics, in terms of one fundamental constant, λ_P. It is emphasized that spacetime of special relativities with two invariant scales carries an intrinsic quantum-gravitational character. In an addenda, we also comment on the physical importance of a phase factor that the whole literature on the subject has missed and present a brief critique of . In addition, we remark that the most natural and physically viable shall require momentum-space and spacetime to be non-commutative with the non-commutativity determined by the spin content and C, P, and T properties of the examined representation space. Therefore, in a physically successful , the notion of spacetime is expected to be deeply intertwined with specific properties of the test particle.

A sample of 39 blazars with well-established rapid variability timescale and bolometric luminosity has been compiled from literature. Based on the assumption that central supermassive black holes (SMBHs) are Kerr black holes, the upper limits of SMBHs were estimated. The masses ranged from 10^7.2M⊙ to 10^9.4M_⊙, showing a distribution of three subclasses: massive flat spectra radio quasars (FSRQs) and smaller mass BL Lacs, occupy separate regions, while medium mass FSRQ and BL Lac object bridge the gap. In addition, we complied a sample of radio galaxies including 9 sources for which their black holes masses have been derived from the M_BH-σ correlation and their optical and infrared data have been well observed. We find that the intrinsic accretion rates are quite different between FSRQs, BL Lacs and the radio galaxies. The diagram of the intrinsic accretion rate–luminosity relations shows that FSRQs occur in the earlier, high luminosity, violent phase of galactic evolution sequence, while BL Lacs occur in the low luminosity, transition phase between quasars and radio galaxies, and the radio galaxies occur in the late stage of the elliptical galaxy evolution sequence. Our theoretical results prove that the evolutionary track of the elliptical galaxy evolutionary sequence is from FSRQs to BL Lacs and then to the radio galaxies. The evolution diagram of blazars derived in this paper seems to be similar to Hertzsprung–Russell diagram of star evolution.

We investigate the weak-field limit of scalar-tensor theory of gravity and show that results are directly depending on the coupling and self-interaction potential of the scalar field. In particular, corrections are derived for the Newtonian potential. We discuss astrophysical applications of the results, in particular the flat rotation curves of spiral galaxies.

We study an exponential stretch–rotation (ESR) transformation, γ_ij=e^∊_ikmθ_me^ϕ_ke^-∊_jknθ_n, of a three-dimensional metric γ_ij of space-like hypersurfaces embedded in a four-dimensional space–time, where ϕ_k are logarithms of the eigenvalues of γ_ij, θ_k are rotation angles, and ∊_ijk is a fully anti-symmetric symbol. This tensorial exponential transformation generalizes particular exponential transformations used previously in cases of spatial symmetry. General formulae are derived that relate γ_ij and its differentials to ϕ_k, θ_k and their differentials in a compact form. The evolution part of Einstein's equations formulated in terms of ESR variables describes time evolution of the metric at every point of a hyper-surface as a continuous stretch and rotation of a triad associated with the main axes of the metric tensor in a tangential space. An ESR 3+1 formulation of Einstein's equations may have certain advantages for long-term stable integration of these equations.