Bootstrapping a Five-Loop Amplitude Using Steinmann Relations
  The analytic structure of scattering amplitudes is restricted by Steinmann relations, which enforce the vanishing of certain discontinuities of discontinuities. We show that these relations dramatically simplify the function space for the hexagon function bootstrap in planar maximally supersymmetric Yang-Mills theory. Armed with this simplification, along with the constraints of dual conformal symmetry and Regge exponentiation, we obtain the complete five-loop six-particle amplitude. 
Simon Caron-Huot, Lance J. Dixon, Andrew McLeod and Matt von Hippel
hep-th hep-ph