Exact baryon-meson relation for $b \to s ν\barν$

We derive an exact relation among the normalized branching fractions of $Λ_b \to Λν\barν$ and $B \to K^{(\ast)} ν\barν$, within the lepton-number-conserving effective Hamiltonian in which only active neutrinos contribute to the invisible final state. Although the effective Hamiltonian contains 18 in