Gravitational causality and the self-stress of photons
Résumé
We study causality in gravitational systems beyond the classical limit. Using on-shell methods, we consider the 1-loop corrections from charged particles to the photon energy-momentum tensor — the self-stress — that controls the quantum interaction between two on-shell photons and one off-shell graviton. The self-stress determines in turn the phase shift and time delay in the scattering of photons against a spectator particle of any spin in the eikonal regime. We show that the sign of the β-function associated to the running gauge coupling is related to the sign of time delay at small impact parameter. Our results show that, at first post-Minkowskian order, asymptotic causality, where the time delay experienced by any particle must be positive, is respected quantum mechanically. Contrasted with asymptotic causality, we explore a local notion of causality, where the time delay is longer than the one of gravitons, which is seemingly violated by quantum effects.
Mots clés
Effective Field Theories
Scattering Amplitudes
tensor: energy-momentum
approximation: classical
effect: quantum
photon: scattering
photon: on-shell
coupling: gauge
causality
time delay
gravitation
graviton
spectator
charged particle
quantum mechanics
phase shift
off-shell
impact parameter
spin
eikonal
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