Analytical result for dimensionally regularized massless master non-planar double box with one-leg off shell

The dimensionally regularized massless non-planar double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e., with p12=q2≠0, and three legs on shell, pi2=0, i=2,3,4, is analytically calculated for general values of q2 and the Mandelstam variables s,t and u (not necessarily restricted by the physical condition s+t+u=q2). An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q2,s,t and u, and simple finite two- and three-fold Mellin–Barnes integrals of products of gamma functions which are easily numerically evaluated for arbitrary non-zero values of the arguments.