Warm Higgs G-inflation: predictions and constraints from Planck 2015 likelihood

Abstract

We reconsider a recently proposed warm G-inflation scenario in which the Galileon scalar field concurrently dissipates its kinetic energy as the radiation fluid throughout inflation and the universe smoothly enters into a radiation dominated era without going through the reheating phase. It is shown that the perturbed second-order Langevin equation can be nicely simplified and solved by defining the Galileon dissipation factor, $Q_{G} = \frac{Q}{\mathcal{B}}$, resulting in a power spectrum utilizing a Green function approach for the dissipative coefficient independent of temperature. However, for a dissipation coefficient depending on temperature, the perturbed inflaton and radiation field equations will be coupled in the high temperature regime. Therefore, the produced radiation backreacts on the power spectrum, modifying it with a growing mode function in the high dissipation regime. Finally, a model is proposed in which the standard Higgs boson dissipates into light mediator fields, for instance, fermions with a linear temperature dependent dissipative coefficient which can act as inflaton, thanks to the Galileon-like non-linear derivative interaction. The generated primordial perturbations in the G-dominant regime is in excellent agreement with Planck 2015 likelihood+ TTTEEE+BAO at large scales despite its large self-coupling $λ\sim 0.13$ through accommodating many light mediator fields. However, although such primordial perturbations may also get amplified by several orders of magnitude at small scales due to the presence of the growing mode function, warm G-inflation shows a striking feature in that the growing mode can be controlled or completely disappeared by decreasing the value of the propagating sound speed $c_{s}$.