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