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We investigate the phenomenology of warm inflation and present generic results about the evolution of the inflaton and radiation fields. The general conditions required for warm inflation to take place are derived and discussed. A comprehensive approach is presented for the generation of thermally induced adiabatic and isocurvature perturbations and the amplitude of their spectra calculated. In addition we derive the ratio of tensor-to-scalar perturbations and find the spectral indices for adiabatic, isocurvature and tensor perturbations formed in the warm inflationary era. These results are presented in a simplified and compact approach that is generally applicable. Our results are illustrated by inflation models with polynomial and exponential potentials. We compare our analytic results against numerical models and find excellent agreement. Finally, presently available data are used to put constraints on warm inflation and we discuss how near-future observations may distinguish the warm inflationary scenario from standard supercooled inflation. The main observable difference is the different scalar-to-tensor ratio, and that the consistency relation between this and the slope of tensor perturbations does not hold for warm inflation.
Taylor et al. (Thu,) studied this question.