Einstein-aether models III: conformally static metrics, perfect fluid and scalar fields

Abstract

The asymptotic properties of conformally static metrics in Einstein-aether theory with a perfect fluid source and a scalar field are analyzed. In case of perfect fluid, some relativistic solutions are recovered such as: Minkowski spacetime, the Kasner solution, a flat FLRW space and static orbits depending on the barotropic parameter $\gamma$. To analyze locally the behavior of the solutions near a sonic line $v^2=\gamma-1$, where $v$ is the tilt, a new "shock" variable is used. Two new equilibrium point on this line are found. These points do not exist in General Relativity when $1 <\gamma<2 $. In the limiting case of General Relativity these points represent stiff solutions with extreme tilt. Lines of equilibrium points associated with a change of causality of the homothetic vector field are found in the limit of General Relativity. For non-homogeneous scalar field $\phi(t,x)$ with potential $V(\phi(t,x))$ the symmetry of the conformally static metric restrict the scalar fields to be considered to $ \phi(t,x)=\psi (x)-\lambda t, V(\phi(t,x))= e^{-2 t} U(\psi(x))$, $U(\psi)=U_0 e^{-\frac{2 \psi}{\lambda}}$. An exhaustive analysis (analytical or numerical) of the stability conditions is provided for some particular cases.