Hilbert space in the flat limit of AdS/CFT. I. Massive particles
The flat limit of AdS$_4$ spacetime corresponds, at the level of the symmetry algebra, to the In\"on\"u--Wigner contraction $\mathfrak{so}(2,3) \to \mathfrak{iso}(1,3)$. We describe the emergence of the Hilbert space of massive scattering states of arbitrary integer spin $s$ from unitary lowest-weight representations $...