Latest in infrared finite scattering! https://arxiv.org/abs/2402.00102
Any non-trivial scattering in quantum gravity will produce non-trivial low frequency effects related to the production of gravitational memory. At null infinity, the memory manifests itself in the presence of unitarily inequivalent Hilbert space sectors each with a definite value of the memory. The memory is not Lorentz-invariant so these states with definite memory do not have a finite value of Lorentz charge operators (e.g. angular momentum). This was worked out by Ashtekar long ago.
We show how to stitch together these memory states into Hilbert spaces that have a well-defined Lorentz charge. There are still many inequivalent Hilbert spaces, but now we have a large supply of states which include both the memory and Lorentz charges and can be used to do scattering. More to come…
Kartik Prabhu