HIGGS INFLATION AROUND THE SYMMETRIC POINT

A novel generalized Higgs inflation scenario is studied, where inflation takes place near the symmetric point of the “Mexican hat” potential, as opposed to the standard Higgs inflation which takes place at large field values away from the symmetric point. When minimally coupled to gravity, inflation near the symmetric point leads to large tensor-to-scalar ratio which is ruled out by CMB observations, while requiring super-Planckian Higgs VEV which also acts as the axion decay constant (super-Planckian values of the decay constant are theoretically disfavored, for example by the swampland conjectures). It is shown that both of the aforementioned problems can be resolved by considering non-minimal coupling of the Higgs field to the scalar curvature of spacetime. This requires sufficiently large non-minimal coupling parameter, and produces similar results for the scalar spectral index and tensor-to-scalar ratio to the standard Higgs inflation, and the Starobinsky model. The Higgs field under consideration can in principle be identified with the Standard Model Higgs scalar, in which case an extremely large non-minimal coupling is required (in order to reproduce CMB-aligned predictions), which can also be theoretically problematic. A more likely scenario is a hidden sector Higgs-like field, such as the Peccei–Quinn field, where a smaller non-minimal coupling is acceptable. The proposed model offers an alternative to the simplest single-field models of inflation, especially of Higgs and Peccei-Quinn type, while fitting the CMB observations of primordial power spectra. An advantage of such models in the vast landscape of inflationary theories is simplicity: no ad hoc scalar fields are assumed to exist purely to explain inflation, since both Higgs and Peccei-Quinn fields are motivated by particle physics considerations.