Causality, Higher-Spin Particles and Large N QCD

by Sandipan Kundu (Johns Hopkins University)

Tuesday 13 Jul 2021, 15:00 → 16:00 Europe/Madrid

IFAE Virtual Seminar Room (IFAE)

I will show that metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. I will discuss many surprising implications of the above bound for large N QCD coupled to gravity.

HigherSpinCausality_IFAE.pdf