gg → Z Z: analytic two-loop results for the low- and high-energy regions

We compute next-to-leading order virtual two-loop corrections to the process gg → Z Z in the low- and high-energy limits, considering the contributions with virtual top quarks. Analytic results for all 20 form factors are presented including expansion terms up to $$ 1/{m}_t^{12} $$ 1 / m t 12 and $$ {m}_t^{32} $$ m t 32 . We use a Padé approximation procedure to extend the radius of convergence of the high-energy expansion and apply this approach to the finite virtual next-to-leading order corrections.