Testing high-energy factorization beyond the next-to-leading-logarithmic accuracy

By taking the high-energy limit of the two-loop and the three-loop four-point amplitudes in the maximally supersymmetric N = 4 Yang-Mill theory (MSYM), we test the validity of the loop expansion of the high-energy amplitude, beyond the next-to-leadinglogarithmic (NLL) accuracy. We compute the three-loop Regge trajectory, and the two-loop and three-loop coefficient functions. These quantities are relevant for the BFKL evolution beyond NLL, as well as building MSYM two-loop and three-loop amplitudes with many legs in the high-energy limit, which in turn may be used as a powerful check of the evaluation of the corresponding exact amplitudes.