Dispersive bounds for local form factors in Λb → Λ transitions

We investigate the ten independent local form factors relevant to the b-baryon decay Λb→Λℓ+ ℓ-, combining information of lattice QCD and dispersive bounds. We propose a novel parametrization of the form factors in terms of orthonormal polynomials that diagonalizes the form factor contributions to the dispersive bounds. This is a generalization of the unitarity bounds developed for meson-to-meson form factors. In contrast to ad hoc parametrizations of these form factors, our parametrization provides a degree of control of the form-factor uncertainties at large hadronic recoil. This is of phenomenological interest for theoretical predictions of, e.g., Λb→Λγ and Λb→Λ ℓ+ ℓ- decay processes.