All-helicity symbol alphabets from unwound amplituhedra

Here we review an algorithm for determining the branch points of general amplitudes in planar <em>N</em> = 4 super-Yang-Mills theory from amplituhedra. We demonstrate how to use the recent reformulation of amplituhedra in terms of ‘sign flips’ in order to streamline the application of this algorithm to amplitudes of any helicity. In this way we recover the known branch points of all one-loop amplitudes, and we find an ‘emergent positivity’ on boundaries of amplituhedra.