Gravitational dynamics in Higgs inflation: Preinflation and preheating
  with an auxiliary field
  The dynamics of both the preinflationary and the preheating epochs for a
model consisting of a Higgs inflaton plus an additional auxiliary field are
studied in full General Relativity. The minimally coupled auxiliary field
allows for parametric-type resonances that successfully transfer energy from
the inflaton condensate to particle excitations in both fields. Depending on
the interaction strengths of the fields, the broad resonance periods lead to
structure formation consisting of large under/over-densities, and possibly the
formation of compact objects. Moreover, when confronting the same model to
multi-field inhomogeneous preinflation, the onset of inflation is shown to be a
robust outcome. At relatively large Higgs values, the non-minimal coupling acts
as a stabilizer, protecting the dynamics of the inflaton, and significantly
reducing the impact of perturbations in other fields and matter sectors. These
investigations further confirm the robustness of Higgs inflation to multi-field
inhomogeneous initial conditions, while putting in evidence the formation of
complex structures during the reheating.
