The S-matrix Bootstrap II: Two Dimensional Amplitudes
  We consider constraints on the S-matrix of any gapped, Lorentz invariant quantum field theory in 1 + 1 dimensions due to crossing symmetry and unitarity. In this way we establish rigorous bounds on the cubic couplings of a given theory with a fixed mass spectrum. In special cases we identify interesting integrable theories saturating these bounds. Our analytic bounds match precisely with numerical bounds obtained in a companion paper where we consider massive QFT in an AdS box and study boundary correlators using the technology of the conformal bootstrap. 
Miguel F. Paulos, Joao Penedones, Jonathan Toledo, Balt C. van Rees,   Pedro Vieira
hep-th