From Positivity to Gravity: Constraints on Massive Higher Spins

Abstract: In this talk, I will explore how causality constraints on scattering amplitudes — known as positivity bounds — impose powerful restrictions on the Effective Field Theory (EFT) of massive higher-spin particles. Focusing on spin-3/2 as a case study, I will demonstrate how consistency conditions require the emergence of gravity, and how these constraints are connected to swampland conjectures. Additionally, I will discuss how further nontrivial bounds arise in the rigid limit, where gravity is decoupled,  constraining the EFT landscape for spin-1/2 particles.