F(1) for B (forward) D*ln from lattice QCD

The authors would like to determine |V{sub cb}| from the exclusive semi-leptonic decay B{yields}D*lv. The differential decay rate is d{Lambda}/dw = G{sub F}{sup 2}/4{pi}{sup 3}(w{sup 2}-1){sup 1/2}m{sub D*}{sup 3} (m{sub B}-m{sub D*}){sup 2}G(w)|V{sub cb}|{sup 2}|F{sub B{yields}D*}(w)|{sup 2}, where w = v {center_dot} v{prime} and G(1) = 1. At zero recoil (w = 1) heavy-quark symmetry requires F{sub B{yields}D*}(1) to be close to 1. So, |V{sub cb}| is determined by dividing measurements of d{Lambda}/dw by the phase space and well-known factors, and extrapolating to w {yields} 1. This yields |V{sub cb}|F{sub B{yields}D*}(1), and F{sub B{yields}D*}(1) is taken from ''theory''. To date models [1] or a combination of a rigorous inequality plus judgement [2] have been used to estimate F{sub B{yields}D*}(1) - 1. In this work [3] they calculate F{sub B{yields}D*}(1) with lattice gauge theory, in the so-called quenched approximation, but the uncertainty from quenching is included in the error budget.