About the possibility of gravitational emission from the recombination of a delocalized mass

A well-known thought experiment is revisited in which a delocalized particle is quickly recombined while another particle probes its gravitational field. Assuming the gravitational field is quantum, some tension between causality and complementarity principles has been shown to possibly arise in this configuration, key to its proposed resolution being graviton emission by the recombining particle.

The focus of this talk is on the conditions for graviton emission adding to previous considerations. In particular, it is shown that there is apparently a threshold value for the delocalized mass (which can be estimated) below which no graviton emission is possible however fast the recombination is (this not affecting anyway the resolution of the tension above). Implications of this for collapse models of Diosi and Penrose are discussed, as well as connections with the so-called minimum-length metric (a metric description of spacetime with a minimum length built in).

We briefly describe also, a (naive) proposal for turning part of the thought experiment into something real. (elaboration on 2209.10355, and on 2307.09354 (with P. Pieri))