Some like it hot: $R^2$ heals Higgs inflation, but does not cool it

Understand

Strong coupling in Higgs inflation at high energies hinders a joint description of inflation, reheating and low-energy dynamics.

• The situation may be improved with a proper UV completion of the model.
• A well-defined self-consistent way is to introduce an $R^2$-term into the action.
• In this modified model the strong coupling scale returns back to the Planck scale, which justifies the use of the perturbative methods in studies of the model dynamics after inflation.