A lattice study of the form factors A(0) and A(3) in the decay (B)over-bar(0)->rho(+)l(-)(nu)over-bar(l)

We report on a lattice calculation of the form factors A(0) and A(3) for the pseudoscalar to vector meson semileptonic decay (B) over bar(0) --> rho(+)l(-)(1). We find that resonant (or pole-type) contributions alone are unable to describe these two form factors simultaneously. For the quantity A(0)(q(2) = 0), which is important phenomenologically for the determination of \V-ub\, we extract a range of values, A(0)(q(2) = 0) = (0.16-0.35)(-6)(+9), where the range is due to systematic uncertainty and the quoted error is statistical. We have also determined A(2)(q(2) = 0) = 0.28(-6-5)(+9+4)