Higgs inflation in metric and Palatini formalisms: Required suppression of higher dimensional operators

Understand

We investigate the sensitivity of Higgs(-like) inflation to higher dimensional operators in the nonminimal couplings and in the potential, both in the metric and Palatini formalisms.

• We find that, while inflationary predictions are relatively stable against the higher dimensional operators around the attractor point in the metric formalism, they are extremely sensitive in the Palatini one: for the latter, inflationary predictions are spoiled by $|\xi_4| \gtrsim 10^{-6}$ in the nonminimal couplings $(\xi_2 \phi^2 + \xi_4 \phi^4 + \cdots)R$, or by $|\lambda_6| \gtrsim 10^{-16}$ in the Jordan-frame potential $\lambda_4 \phi^4 + \lambda_6 \phi^6 + \cdots$ (both in Planck units).
• This extreme sensitivity results from the absence of attractor in the Palatini formalism.
• Our study underscores the challenge of realizing inflationary models with the nonminimal coupling in the Palatini formalism.