Constraining scalar-gauss-bonnet inflation by reheating, unitarity and PLANCK

We revisit the inflationary dynamics in detail for theories with Gauss-Bonnet gravity coupled to scalar functions in light of PLANCK. Considering a chaotic inflationary scenario for two models involving inflaton-Gauss-Bonnet coupling with a dimensionless coupling parameter β, we constrain the model parameters by current PLANCK data. For non-zero β, we get a big cosmologically viable region in the space of (m,β), where m is the mass of inflaton. Further, we have studied the reheating constraints and unitarity bound on β by examining 2-graviton →2-graviton (hh→hh) scattering amplitude in flat background. For linear Gauss-Bonnet coupling function, we obtain β≲103, with the condition β(m/MP)2≃10−4. For quadratic Gauss-Bonnet coupling function we have found even tighter constraint on β, coming from reheating consideration. However, study of the Higgs inflation scenario in the presence of Gauss-Bonnet term turned out to be strongly disfavoured.