Boundaries of Amplituhedra and NMHV Symbol Alphabets at Two Loops

Understand

In this sequel to arXiv:1711.11507 we classify the boundaries of amplituhedra relevant for determining the branch points of general two-loop amplitudes in planar $\mathcal{N}=4$ super-Yang-Mills theory.

• We explain the connection to on-shell diagrams, which serves as a useful cross-check.
• We determine the branch points of all two-loop NMHV amplitudes by solving the Landau equations for the relevant configurations and are led thereby to a conjecture for the symbol alphabets of all such amplitudes.