Averaging anisotropic cosmologies

Averaging inhomogeneous Newtonian cosmologies

Idealizing matter as a pressureless fluid and representing its motion by a peculiar-velocity field superimposed on a homogeneous and isotropic Hubble expansion, we apply (Lagrangian) spatial averaging on an arbitrary domain D to the (nonlinear) equations of Newtonian cosmology and derive an exact, general equation for the evolution of the (domain dependent) scale factor aD (t). We consider the ...

Anisotropic Born-Infeld Cosmologies

Anisotropic cosmological spacetimes are constructed from spherically symmetric solutions to Einstein’s equations coupled to nonlinear electrodynamics and a positive cosmological constant. This is accomplished by finding solutions in which the roles of r and t are interchanged for all r > 0 (i.e. r becomes timelike and t becomes spacelike). Constant time hypersurfaces have topology R × S and in ...

Anisotropic scalar-tensor cosmologies.

We examine homogeneous but anisotropic cosmologies in scalar-tensor gravity theories, including Brans-Dicke gravity. We present a method for deriving solutions for any isotropic perfect fluid with a barotropic equation of state (p ∝ ρ) in a spatially flat (Bianchi type I) cosmology. These models approach an isotropic, general relativistic solution as the expansion becomes dominated by the barot...

Anisotropic and Inhomogeneous Cosmologies

Anisotropic Null String Cosmologies

We study string propagation in an anisotropic, cosmological background. We solve the equations of motion and the constraints by performing a perturbative expansion of the string coordinates in powers of c, the world-sheet speed of light. To zeroth order the string is approximated by a tensionless string (since c is proportional to the string tension T ). We obtain exact, analytical expressions ...