Gravitational causality and the self-stress of photons

Abstract

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.

Crossing Symmetric Spinning S-matrix Bootstrap: EFT bounds

“…. We call the conditions (119) collectively as P B γ C 16 . We note here that the positivity conditions P B γ C in this case are identical to the ones for massive scalar in [25,29].…”

“…The following conditions are obtained for the parity even sector. Now let us consider the conditions coming from the third matrix in (C. 16). We find that analysing the 2 × 2 principal minors is sufficient for our purposes and we obtain,…”

“…In recent times, there has been an increase in interest in establishing two-sided bounds on ratios of parameters in front of higher-dimensional operators in the EFT lagrangians. Recent work in this direction include [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Starting from the original attempts to constrain scalar EFTs, research has been extended to external particles carrying spin [7,21,22].…”

Causality constraints on black holes beyond GR

“…For recent works discussing the notion of causality in the gravitational context, we point the reader to e.g. [17][18][19][20][21][22].…”

An S -matrix approach to gravitational-wave physics

“…One could also include electro-magnetic interactions as considered in[34] or standard model contributions as in e.g [35]. but here we will only consider the exchange of the graviton and focus on the gravitational sector.…”