Non-Gaussianity from two-field warm inflation

Two-field models are introduced in the warm inflation to analyze the primordial non-Gaussianity of gauge-invariant perturbation. With the assumptions of slow-roll approximation, strong dissipation and temperature independence of dissipative coefficients, bispectrum and nonlinearity functions are analytically obtained via the Green's function method. In our analysis, thermal effects of nonadiabaticity and entropy fluctuations in warm inflation contribute mainly to the non-Gaussianity. The former is characterized by the slow-roll parameter $\ensuremath{\beta}$, a unique parameter of warm inflation, and the latter is associated with the perturbations of cosmic temperature, interpreted as thermal fluctuations from the thermalized radiation bath. Therefore, compared to the cold inflation model, the non-Gaussianity form of the warm inflation has significantly different physical meanings. Two models with constant and field-dependent dissipative coefficients are introduced, and both confirm that a stronger damping will enhance the non-Gaussianity. From the numerical results, it is still possible to predict an observably large tensor-to-scalar ratio, with amplitude of $r\ensuremath{\sim}{10}^{\ensuremath{-}3}--{10}^{\ensuremath{-}4}$.