Zero-recoil sum rules for Λb → Λc form factors

We set up a zero recoil sum rule to constrain the form factors of the Λb→ΛcΛb→Λc transition. Our results are compared with the recent lattice calculation for these transitions. We find the same situation as in the case for B→D⁎B→D⁎: The lattice results practically saturate the sum rules, leaving basically no room for excited states.