Speaker
Description
We study the scattering of identical massive spin-2 particles using S-matrix bootstrap methods. Starting from the most general on-shell cubic and quartic interactions, we impose unitarity, analyticity, crossing symmetry, and improved high-energy behaviour to derive bounds on the cubic couplings and particle spectrum. To organize the polarization dependence, we work with a basis of dual tensor structures rather than individual helicity amplitudes. We derive dispersive sum rules for parity-even cubic interactions with at most two derivatives, imposing the cancellations required for the amplitude to grow no faster than O(E^4) at high energies. As an application, we use these sum rules to bound the coupling of a pair of charge-one massive spin-2 Kaluza–Klein modes to a charge-two massive spin-2 mode, relative to their universal coupling to the massless graviton, as well as the coupling of the Kaluza–Klein modes to a massless scalar.