Browsing by Author "M. Zubair"

Now showing 1 - 4 of 4
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    Dynamical instability and expansion-free condition in f (r, t) gravity
    (European. Physics Journal C, 2015) Ifra Noureen; M. Zubair
    A dynamical analysis of a spherically symmetric collapsing star surrounded by a locally anisotropic environment under an expansion-free condition is presented in f (R, T ) gravity, where R corresponds to the Ricci scalar and T stands for the trace of the energy momentum tensor. The modified field equations and evolution equations are reconstructed in the framework of f (R, T ) gravity. In order to acquire the collapse equation we implement the perturbation on all matter variables and dark source components comprising the viable f (R, T ) model. The instability range is described in the Newtonian and post-Newtonian approximation. It is observed that the unequal stresses and density profile define the instability range rather than the adiabatic index. However, the physical quantities are constrained to maintain positivity of the energy density and a stable stellar configuration.
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    Evolution of axially symmetric anisotropic sources in f (r, t) gravity
    (The European Physical Journal C, 2015) M. Zubair; Ifra Noureen
    We discuss the dynamical analysis in f (R, T ) gravity (where R is the Ricci scalar and T is the trace of the energy momentum tensor) for gravitating sources carrying axial symmetry. The self-gravitating system is taken to be anisotropic and the line element describes an axially symmetric geometry avoiding rotation about the symmetry axis and meridional motions (zero vorticity case). The modified field equations for axial symmetry in f (R, T ) theory are formulated, together with the dynamical equations. Linearly perturbed dynamical equations lead to the evolution equation carrying the adiabatic index , which defines the impact of a non-minimal matter to geometry coupling on the range of instability for Newtonian and post-Newtonian approximations.
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    Impact of extended starobinsky model on evolution of anisotropic, vorticity-free axially symmetric sources
    (Journal of Cosmology and Astroparticle Physics, 2015) Ifra Noureen; Abdul Aziz Bhatti; M. Zubair
    We study the implications of Rn extension of Starobinsky model on dynamical instability of Vorticity-free axially symmetric gravitating body. The matter distribution is considered to be anisotropic for which modified field equations are formed in context of f(R) gravity. In order to achieve the collapse equation, we make use of the dynamical equations, extracted from linearly perturbed contracted Bianchi identities. The collapse equation carries adiabatic index 􀀀 in terms of usual and dark source components, defining the range of stability/insatbility in Newtonian (N) and post-Newtonian (pN) eras. It is found that supersymmetric supergravity f(R) model represents the more practical substitute of higher order curvature corrections.
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    Shear-free condition and dynamical instability in f (r, t) gravity
    (The European Physical Journal C, 2015) Ifra Noureen; M. Zubair; A.A. Bhatti; G. Abbas
    The implications of the shear-free condition on the instability range of an anisotropic fluid in f (R, T ) are studied in this manuscript. A viable f (R, T ) model is chosen to arrive at stability criterion, where R is Ricci scalar and T is the trace of energy-momentum tensor. The evolution of a spherical star is explored by employing a perturbation scheme on the modified field equations and contracted Bianchi identities in f (R, T ). The effect of the imposed shear-free condition on the collapse equation and adiabatic index is studied in the Newtonian and post-Newtonian regimes.