Viscous Coupled Fluids in Inflationary Cosmology

We consider the inflation produced by two coupled fluids in the flat Friedmann-Robertson-Walker universe. Different cosmological models for describing inflation by use of an inhomogeneous equation of state for the fluid are investigated. The gravitational equations for energy and matter are solved, and analytic representations for the Hubble parameter and the energy density are obtained. Corrections in the energy density for matter inducing the inflation and the coupling with energy are discussed. We analyze the description of inflation induced by non-constant equation-of-state parameters from fluid viscosity. The correspondence between the spectral index and the tensor-to-scalar ratio recently observed by the Planck satellite is considered.