  The main limitation for pre-inflationary breaking of Peccei-Quinn (PQ)
symmetry is the upper bound on the Hubble rate during inflation from axion
isocurvature fluctuations. This leads to a tension between high scale inflation
and QCD axions with Grand Unified Theory (GUT) scale decay constants, which
reduces the potential for a detection of tensor modes at next generation CMB
experiments. We propose a mechanism that excplicitly breaks PQ symmetry via
non-minimal coupling to gravity, that lifts the axion mass above the Hubble
scale during inflation and has negligible impact on today's axion potential.
The initially heavy axion gets trapped at an intermediate minimum during
inflation given by the phase of the non-minimal coupling, before it moves to
its true CP-conserving minimum after inflation. During this stage it undergoes
coherent oscillations around an adiabatically decreasing minimum, which
slightly dilutes the axion energy density, while still being able to explain
the observed dark matter relic abundance. This scenario can be tested by the
combination of next generation CMB surveys like CMB-S4 and LiteBIRD with
haloscopes such as ABRACADABRA or CASPEr-Electric.
