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

The dimensionally regularized massless double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e. with nonzero q2=p12, and three legs on shell, pi2=0, i=2,3,4, is analytically calculated for general values of q2 and the Mandelstam variables s and t. An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q2,s and t, and a one-dimensional integral with a simple integrand consisting of logarithms and dilogarithms.