Warm inflation with non-comoving scalar field and radiation fluid
  We consider a warm inflationary scenario in which the two dominant matter
components present in the early Universe, the scalar field, and the radiation
fluid, evolve with different four-velocities. This cosmological system is
mathematically equivalent to a single anisotropic fluid, evolving with a
four-velocity that is a function of the two independent fluid four-velocities.
Due to the presence of the anisotropic physical parameters, the overall
cosmological evolution is also anisotropic. We derive the gravitational field
equations of the noncomoving scalar field-radiation mixture for a Bianchi type
I geometry. By considering that the decay of the scalar field is accompanied by
a corresponding radiation generation, we formulate the basic equations of the
warm inflationary model in the presence of two noncomoving components. By
adopting the slow roll approximation, we perform a detailed comparison of the
theoretical predictions of the warm inflationary scenario with noncomoving
scalar field and radiation fluid with the observational data obtained by the
Planck satellite, by investigating both the weak dissipation and strong
dissipation limits. Constraints on the free parameters of the model are
obtained in both cases. The functional forms of the scalar field potentials
compatible with the noncomoving nature of warm inflation are also derived.
