Perfect fluid scalar-tensor cosmologies

A method is investigated which enables exact solutions to be found for k=0 Friedmann cosmological models with a perfect fluid satisfying the equation of states p=(γ-1)ρ, where γ is constant and 0≤γ≤2, in scalar-tensor gravity theories with an arbitrary form for the gravitational coupling function ω(φ), which defines the theory. A number of explicit solutions are investigated for p=0 universes and inflationary universes, including those for theories in which ω(φ) has a power-law dependence on the scalar field φ. When p=-ρ new varieties of inflation arise in which a(t)∝tnexp(H0tm).