Graviton Production in Elliptical and Hyperbolic Universes

Abstract

The problem of cosmological graviton creation for homogeneous and isotropic universes with elliptical ($\vae =+1$) and hyperbolical ($\vae =-1$) geometries is addressed. The gravitational wave equation is established for a self-gravitating fluid satisfying the barotropic equation of state $p=(γ-1)ρ$, which is the source of the Einstein's equations plus a cosmological $Λ$-term. The time dependent part of this equation is exactly solved in terms of hypergeometric functions for any value of $γ$ and spatial curvature $\vae$. An expression representing an adiabatic vacuum state is then obtained in terms of associated Legendre functions whenever $γ\neq \frac{2}{3}\; \frac{(2n+1)}{(2n-1)}$, where n is an integer. This includes most cases of physical interest such as $γ=0,\;4/3\;,1$. The mechanism of graviton creation is reviewed and the Bogoliubov coefficients related to transitions between arbitrary cosmic eras are also explicitly evaluated.