On the consistency of warm inflation in the presence of viscosity

This paper studies the stability of warm inflationary solutions when the viscous pressure is taken into account. The latter is a very natural and physically motivated ingredient of warm inflation and is seen to widen the stability range of warm inflation. The spectral index parameters, $n_s$, $n_T$, and their ratio are derived. The corresponding WMAP7 data are used to fix some parameters of the model. Two specific examples are discussed in detail: (i) a potential given by $V(\varphi ,T)=v_1(\varphi )+v_2(T)$, and (ii) a potential of the form $V(\phi, T) = \alpha , v_{1}(\phi) , v_{2}(T)$. In both cases, the viscosity has little impact on the said ratio.