Contiguous redshift parameterizations of the growth index (2009)
Ishak, Mustapha, Dossett, Jason
The growth rate of matter perturbations can be used to distinguish between different gravity theories and to distinguish between dark energy and modified gravity at cosmological scales as an...
Growth factor parametrization in curved space (2009)
Gong, Yungui, Ishak, Mustapha, Wang, Anzhong
The growth rate of matter perturbation and the expansion rate of the Universe can be used to distinguish modified gravity and dark energy models in explaining the cosmic acceleration. We explore here...
More on Lensing by a Cosmological Constant (2008)
Ishak, Mustapha, Rindler, Wolfgang, Dossett, Jason
The question of whether or not the cosmological constant affects the bending of light around a concentrated mass has been the subject of some recent papers. We present here a simple, specific and...
A minimal set of invariants as a systematic approach to higher order gravity models (2008)
Ishak, Mustapha, Moldenhauer, Jacob
Higher-order gravity models have been recently the subject of much attention in the context of cosmic acceleration. These models are derived by adding various curvature invariants to the...
The contribution of the cosmological constant to the deflection angle and the time delays are derived from the integration of the gravitational potential as well as from Fermat's Principle. The...
Ishak, Mustapha, Rindler, Wolfgang, Dossett, Jason, Moldenhauer, Jacob, Allison, Chris
We derive new limits on the value of the cosmological constant, $\Lambda$, based on the Einstein bending of light by systems where the lens is a distant galaxy or a cluster of galaxies. We use an...
The Contribution of the Cosmological Constant to the Relativistic Bending of Light Revisited (2007)
Rindler, Wolfgang, Ishak, Mustapha
We study the effect of the cosmological constant $\Lambda$ on the bending of light by a concentrated spherically symmetric mass. Contrarily to previous claims, we show that when the Schwarzschild-de...
Ishak, Mustapha, Richardson, James, Garred, David, Whittington, Delilah, Nwankwo, Anthony, Sussman, Roberto
We use the Szekeres inhomogeneous relativistic models in order to fit supernova combined data sets. We show that with a choice of the spatial curvature function that is guided by current...
Inverse approach to Einstein's equations for fluids with vanishing anisotropic stress tensor (2007)
Richardson, James, Ishak, Mustapha
We expand previous work on an inverse approach to Einstein Field Equations where we include fluids with energy flux and consider the vanishing of the anisotropic stress tensor. We consider the...
Hirata, Christopher M., Mandelbaum, Rachel, Ishak, Mustapha, Seljak, Uros, Nichol, Robert, Pimbblet, Kevin A., ...
Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright...
Mandelbaum, Rachel, Hirata, Christopher M., Ishak, Mustapha, Seljak, Uros, Brinkmann, Jonathan
The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology, in particular for measuring the effects of dark energy on the growth of structure...
Ishak, Mustapha, Upadhye, Amol, Spergel, David N.
If general relativity is the correct theory of physics on large scales, then there is a differential equation that relates the Hubble expansion function, inferred from measurements of angular...
Remarks on the formulation of the cosmological constant/dark energy problems (2005)
Associated with the cosmic acceleration are the old and new cosmological constant problems, recently put into the more general context of the dark energy problem. In broad terms, the old problem is...
We study future constraints on dark energy parameters determined from several combinations of CMB experiments, supernova data, and weak lensing surveys with and without tomography. In this analysis,...
Ishak, Mustapha, Hirata, Christopher M.
Weak lensing is a potentially robust and model-independent cosmological probe, but its accuracy is dependent on knowledge of the redshift distribution of the source galaxies used. The most robust way...
Dynamical dark energy: Current constraints and forecasts (2004)
Upadhye, Amol, Ishak, Mustapha, Steinhardt, Paul J.
We consider how well the dark energy equation of state $w$ as a function of red shift $z$ will be measured using current and anticipated experiments. We use a procedure which takes fair account of...
On perfect fluid models in non-comoving observational spherical coordinates (2004)
We use null spherical (observational) coordinates to describe a class of inhomogeneous cosmological models. The proposed cosmological construction is based on the observer past null cone. A known...
Spectroscopic source redshifts and parameter constraints from weak lensing and CMB (2004)
Ishak, Mustapha, Hirata, Christopher M.
Weak lensing is a potentially robust and model-independent cosmological probe, but its accuracy is dependent on knowledge of the redshift distribution of the source galaxies used. The most robust way...
Weak lensing and CMB: Parameter forecasts including a running spectral index (2004)
Ishak, Mustapha, Hirata, Christopher M., McDonald, Patrick, Seljak, Uroš
We use statistical inference theory to explore the constraints from future galaxy weak lensing (cosmic shear) surveys combined with the current CMB constraints on cosmological parameters, focusing...
Weak Lensing and CMB: Parameter forecasts including a running spectral index (2003)
Ishak, Mustapha, Hirata, Christopher M., McDonald, Patrick, Seljak, Uros
We use statistical inference theory to explore the constraints from future galaxy weak lensing (cosmic shear) surveys combined with the current CMB constraints on cosmological parameters, focusing...
An inverse approach to Einstein's equations for non-conducting fluids (2003)
We show that a flow (timelike congruence) in any type $B_{1}$ warped product spacetime is uniquely and algorithmically determined by the condition of zero flux. (Though restricted, these spaces...
Adiabatic models of the cosmological radiative era (2001)
Sussman, Roberto A., Ishak, Mustapha
We consider a generalization of the Lemaitre-Tolman-Bondi (LTB) solutions by keeping the LTB metric but replacing its dust matter source by an imperfect fluid with anisotropic pressure $\Pi_{ab} $....
We describe a new interactive database (GRDB) of geometric objects in the general area of differential geometry. Database objects include, but are not restricted to, exact solutions of Einstein's...
Stability of Transparent Spherically Symmetric Thin Shells and Wormholes (2001)
The stability of transparent spherically symmetric thin shells (and wormholes) to linearized spherically symmetric perturbations about static equilibrium is examined. This work generalizes and...
The Tolman VII solution, trapped null orbits and w - modes (2001)
Neary, Nicholas, Ishak, Mustapha, Lake, Kayll
The Tolman VII solution is an exact static spherically symmetric perfect fluid solution of Einstein's equations that exhibits a surprisingly good approximation to a neutron star. We show that this...
Exact Solutions with w - modes (2000)
Ishak, Mustapha, Chamandy, Luke, Neary, Nicholas, Lake, Kayll
An explicit necessary condition for the occurrence of resonance scattering of axial gravitational waves, along with the internal trapping of null geodesics, is proposed for static spherically...
GRLite and GRTensorJ: Graphical user interfaces to the computer algebra system GRTensorII (1999)
Ishak, Mustapha, Musgrave, Peter, Mourra, John, Stern, Jonathan, Lake, Kayll
GRLite and GRTensorJ are first and second generation graphical user interfaces to the computer algebra system GRTensorII. Current development centers on GRTensorJ, which provides fully customizable...