More on the Bending of Light in Quantum Gravity

TL;DR

This paper analyzes quantum corrections to light bending in quantum gravity, considering multiple contributions and confirming previous results while revealing additional quantum effects that do not violate the equivalence principle.

Contribution

It provides a comprehensive analysis of all relevant quantum contributions to light bending in quantum gravity using traditional Feynman diagrams, confirming previous findings and uncovering new quantum effects.

Findings

Graviton double-cut results agree with previous studies.

Massless-scalar and photon double-cut contributions produce non-vanishing quantum effects.

The quantum structure of gravitational amplitudes and the equivalence principle discrepancy remain consistent.

Abstract

We reconsider the long-range effects of the scattering of massless scalars and photons from a massive scalar object in quantum gravity. At the one-loop level, the relevant quantum mechanical corrections could be sorted into the graviton double-cut contributions, massless-scalar double-cut contributions and photon double-cut contributions. In arXiv:1410.7590 and 1609.07477 N.E.J. Bjerrum-Bohr et al. have considered explicitly the implications of the graviton double-cut contributions on the gravitational bending of light and some classical formulations of the equivalence principle, using the modern double-copy constructions and on-shell unitarity techniques. In this article, instead we consider all three contributions and redo the analysis using the traditional Feynman diagrammatic approach. Our results on the graviton double-cut contributions agree with the aforementioned references, which acts as a nontrivial check of previous computations. Furthermore, it turns out that the massless-scalar double-cut contributions and the photon double-cut contributions do leave non-vanishing quantum effects on the scattering amplitudes and the gravitational bending of light. Yet, we find that the general structure of the gravitational amplitudes and the quantum discrepancy of the equivalence principle suggested in the aforementioned references remain intact.