Gamma-ray emission from pulsars

We have attempted to devise a scheme by which it may be possible to identify pulsars which are likely to be γ-ray pulsars. We apply this test to a representative population of pulsars and identify the likely candidates for γ emission. We also discuss some individual cases including the Crab and Vela pulsars

Globular clusters as gamma ray sources

There are indications now that globular clusters contain a large number of low magnetic field millisecond pulsars. Since millisecond pulsars are expected to emit γ -rays due to curvature radiation, it is likely that globular clusters will themselves be sources of γ -rays bright enough to be detectable by present day instruments. Using the expression derived by Scharlemann, Arons & Fawley (1978) of the energy acquired by the electrons moving along the open magnetic field lines of the pulsars we have calculated the likely luminosity of γ -rays from globular clusters. We discuss our results in the light of the calculations reported in the literature based on some of the other models

Constraint On The Cosmological Constant From Gravitational Lenses In An Evolutionary Model Of Galaxies

We study the effect of the cosmological constant on the statistical properties of gravitational lenses in flat cosmologies (Omega_{0}+lambda_{0} = 1). It is shown that some of the lens observables are strongly affected by the cosmological constant, especially in a low--density universe, and its existence might be inferred by a statistical study of the lenses. In particular, the optical depth of the lens distribution may be used best for this purpose without depending much on the lens model. We calculate the optical depth (probabilty of a beam encountering with a lens event) for a source in a new picture of galaxy evolution based on number evolution in addition to pure luminosity evolution. It seems that present day galaxies result from the merging of a large number of building blocks. We have tried to put limit on the cosmological constant in this new picture of galaxy evolution. This evolutionary model of galaxies permits larger value of cosmological constant.Comment: Latex file with two figures, 24 page

Low-mass Solitons from Fractional Charges in Quantum Chromodynamics

Slansky, Goldman, and Shaw have proposed a model to account for the observation of fractionally charged states. We show that in this model, there are expected to be several low-mass solitons (four being in the mass range ∼20-60 MeV) associated with the third homotopy group π3(SU(3)/SO(3))=Z4, besides a low-mass (∼30 MeV) Z2 monopole. Confirmation of these levels and hence of the model has important implications for Cabrera\u27s results on the magnetic monopole. An efficient algorithm for the calculation of π3(G/H) for a general Lie group G and a subgroup H is developed. It is pointed out that solitons associated with the third homotopy group are predicted by some grand-unified-theory scenarios

Gravitational Lensing Bound On The Average Redshift Of Gamma Ray Bursts In Models With Evolving Lenses

Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE 4B catalog can be used to constrain the average redshift $$ of the GRBs. In this paper we investigate the effect of evolving lenses on the of GRBs in different cosmological models of universe. The cosmological parameters $\Omega$ and $\Lambda$ have an effect on the of GRBs. The other factor which can change the $$is the evolution of galaxies. We consider three evolutionary model of galaxies. In particular, we find that the upper limit on$$ of GRBs is higher in evolving model of galaxies as compared to non-evolving models of galaxies.Comment: 23 pages,one plain LaTeX file with three postscript figures This is modified version with recent BATSE efficiency parameter and with the latest F paramete

Gravitational lensing constraint on the cosmic equation of state

Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at cosmological distances suggest that two-third of the energy density of the universe is dominated by dark energy component with an effective negative pressure. This dark energy component is described by the equation of state $p_{x} = w \rho_{x}$ $(w \geq -1)$. We use gravitational lensing statistics to constrain the equation of state of this dark energy. We use $n(\Delta\theta)$, image separation distribution function of lensed quasars, as a tool to probe $w$. We find that for the observed range of $\Omega_m \sim 0.2 - 0.4$, $w$ should lie between $-0.8 \leq w \leq -0.4$ in order to have five lensed quasars in a sample of 867 optical quasars. This limit is highly sensitive to lens and Schechter parameters and evolution of galaxies.Comment: Modified results and inclusion of calculations with new set of parameter

Neutral current effects in parity violating nuclear force

The measurements of the ΔI= 1 part of the parity violating nuclear force when combined with information on neutral current couplings from neutriro scattering and pion production experiments allow an estimate of the isoscalar admixture in the neutral current if it nas a vector axial-vector structure has been shown