Heavy-quark form factors in the large β₀ limit

Heavy-quark form factors are calculated at β₀α_s∼ 1 to all orders in α_s at the first order in 1 / β₀. Using the inversion relation generalized to vertex functions, we reduce the massive on-shell Feynman integral to the HQET one. This HQET vertex integral can be expressed via a ₂F₁ function; the nth term of its ε expansion is explicitly known. We confirm existing results for nlL-1αsL terms in the form factors (up to L= 3), and we present results for higher L.