Northwestern Events Calendar


HEP Seminar: Matthew Lewandowski: Gravitational Causality and the Self-Stress of Photons

When: Monday, January 10, 2022
4:00 PM - 5:00 PM Central

Where: Online

Audience: Faculty/Staff - Student - Post Docs/Docs - Graduate Students

Contact: Samantha Westlake  

Group: Physics and Astronomy High Energy Physics Seminars

Category: Academic


Abstract: We study causality in gravitational systems beyond the classical limit. Using on-shell methods, we consider the one-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.

Speaker: Matthew Lewandowski, Northwestern University 

Host: André de Gouvêa

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