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SUMMARY:Matt Lewandowski (Northwestern U.)
DTSTART:20211027T163000Z
DTEND:20211027T173000Z
DTSTAMP:20260423T024617Z
UID:CMU-TP/37
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/CMU-TP/37/">
 Gravitational Causality and the Self-Stress of Photons</a>\nby Matt Lewand
 owski (Northwestern U.) as part of Carnegie Mellon theoretical physics\n\n
 \nAbstract\nWe study causality in gravitational systems beyond the classic
 al limit.  Using on-shell methods\, we consider the one-loop corrections f
 rom charged particles to the photon energy- momentum tensor —the self-st
 ress— 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 par
 ticle of any spin in the eikonal regime.  We show that the sign of the bet
 a-function associated to the running gauge coupling is related to the sign
  of time delay at small impact parameter.  Our results show that\, at firs
 t post-Minkowskian order\, asymptotic causality\, where the time delay exp
 erienced by any particle must be positive\, is respected quantum mechanica
 lly.  Contrasted with asymptotic causality\, we explore a local notion of 
 causality\, where the time delay is longer than the one of gravitons\, whi
 ch is seemingly violated by quantum effects.\n
LOCATION:https://researchseminars.org/talk/CMU-TP/37/
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