Ultra-Planckian scattering from a QFT for gravity

Quantum quadratic gravity (QQG) is a proposal for a UV complete quantum field theory of gravity (Stelle 1977).
Its perturbative expansion displays unitarity without positivity.
We calculate ultra-Planckian scattering amplitudes and cross sections and show that this lack of positivity is associated with cancellations that give good high energy behaviour.
Ultra-Planckian scattering may then have features in common with the QCD description of high energy scattering.