Zero-Recoil Sum Rules for ${\Lambda }_b\to {\Lambda }_c$ Form Factors

Abstract

We set up a zero recoil sum rule to constrain the form factors of the ${\Lambda }_b\to {\Lambda }_c$ transition. Our results are compared with the recent lattice calculation for these transitions. We find the same situation as in the case for $B\to D^{\ast }$: The lattice results practically saturate the sum rules, leaving basically no room for excited states.

Comments: 8 pages, 5 figures