  We perform an extensive analysis of linear fluctuations during preheating in
Higgs inflation in the Einstein frame, where the fields are minimally coupled
to gravity, but the field-space metric is nontrivial. The self-resonance of the
Higgs and the Higgsed gauge bosons are governed by effective masses that scale
differently with the nonminimal couplings and evolve differently in time.
Coupled metric perturbations enhance Higgs self-resonance and make it possible
for Higgs inflation to preheat solely through this channel. For $\xi\gtrsim
100$ the total energy of the Higgs-inflaton condensate can be transferred to
Higgs particles within $3$ $e$-folds after the end of inflation. For smaller
values of the nonminimal coupling preheating takes longer, completely shutting
off at around $\xi\simeq 30$. The production of gauge bosons is dominated by
the gauge boson mass and the field space curvature. For large values of the
nonminimal coupling $\xi \gtrsim 1000$, it is possible for the Higgs condensate
to transfer the entirety of its energy into gauge fields within one
oscillation. For smaller values of the nonminimal coupling gauge bosons decay
very quickly into fermions, thereby shutting off Bose enhancement. Estimates of
non-Abelian interactions indicate that they will not suppress preheating into
gauge bosons for $\xi \gtrsim 1000$.
