Mandelstam cuts and lightlike Wilson loops in N=4 supersymmetry

We perform an analytic continuation of the two-loop remainder function for the six-point planar maximally helicity violating amplitude in N=4 supersymmetry, found by Goncharov, Spradlin, Vergu and Volovich from the lightlike Wilson loop representation. The remainder function is continued into a physical region, where all but two energy invariants are negative. It turns out to be pure imaginary in the multi-Regge kinematics, which is in agreement with the predictions based on the Steinmann relations for the Regge poles and Mandelstam cut contributions. The leading term correctly reproduces the expression calculated by one of the authors in the Balitsky-Fadin-Kuraev-Lipatov approach, while the subleading term presents a result that has not been found before with the use of unitarity techniques. This finding supports the applicability of the Wilson loop approach to the planar maximally helicity violating amplitudes in N=4 supersymmetry.