Browsing by Author "Muhammad Sharif"

Now showing 1 - 4 of 4
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    Cosmological evolution of pilgrim dark energy
    (Astrophys Space Sci, 2014) Muhammad Zubair; Muhammad Sharif
    We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of ωϑ and ω ϑ . We conclude that the consistent value of parameter μ is μ<0 in accordance with the current Planck and WMAP9 results.
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    Dynamical instability of expansion-free collapse in f (t) gravity
    (International Journal of Theoretical Physics, 2014) Muhammad Sharif; Shamaila Rani
    In this paper, we analyze the dynamical instability of a spherically symmetric collapsing star in the context of f (T ) gravity. For this purpose, we assume power-law f (T ) model with non-dissipative anisotropic fluid distribution under expansion-free condition. The perturbation scheme is applied to all matter, metric and f (T ) functions. We formulate dynamical equations using contracted Bianchi identities to investigate dynamical instability ranges in Newtonian and post-Newtonian regimes. It is found that the instability ranges of expansion-free fluid are independent of adiabatic index but depend on radial density profile, anisotropic pressure and torsion terms.
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    Galactic halo wormhole solutions in gravity
    (Advances in High Energy Physics, 2014) Muhammad Sharif; Shamaila Rani
    The proposal of galactic halo region is based on the idea that dark halos contain some characteristics needed to support traversable wormhole solutions. We explore wormhole solutions in this region in the framework of generalized teleparallel gravity. We consider static spherically symmetric wormhole space time with flat galactic rotational curves and obtain expressions of matter components for no diagonal tetrad. The effective energy-momentum tensor leads to the violation of energy conditions which may impose condition on the normal matter to satisfy these conditions. We take two well-known (𝑇) models in exponential and logarithmic forms to discuss wormhole solutions as well as the equilibrium condition. It is concluded that wormhole solutions violating weak energy condition are obtained for both models with stable configuration.
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    Lemaitre-tolman-bondi dust cloud collapse in brans-dicke gravity
    (Modern Physics Letters A, 2014) Muhammad Sharif; Rubab Manzoor
    This paper investigates the phenomenon of gravitational collapse of Lemaitre–Tolman- Bondi (LTB) model in the presence of Brans–Dicke (BD) scalar field with nonzero potential field. We find a class of solutions by taking perfect fluid as well as scalar field and check the validity of weak energy conditions. It turns out that two different types of singularities are formed in the presence of scalar field. We conclude that the end state of gravitational collapse turns out to be a black hole (BH) contrary to general relativity (GR).