We consider how Higgs Inflation can be observationally distinguished from variants based on gauge singlet scalar extensions of the Standard Model , in particular where the inflaton is a non-minimally coupled gauge singlet scalar ( S -inflation ) .
We show that radiative corrections generally cause the spectral index n to decrease relative to the classical value as the Higgs mass is increased if the Higgs boson is the inflaton , whereas n increases with increasing Higgs mass if the inflaton is a gauge singlet scalar .
The accuracy to which n can be calculated in these models depends on how precisely the reheating temperature can be determined .
The number of Einstein frame e-foldings \tilde { N } is similar in both models , with \tilde { N } \approx 58 - 61 for singlet inflation compared with \tilde { N } \approx 57 - 60 for Higgs inflation .
This allows the spectral index to be calculated to an accuracy \Delta n = \pm 0.001 .
Provided the Higgs mass is above \approx 135 { GeV } , a combination of a Higgs mass measurement and a precise determination of n will enable Higgs Inflation and S -inflation to be distinguished .