Lattice calculation of the Isgur-Wise functions tau₁/₂ and tau₃/₂ with dynamical quarks

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We perform a dynamical lattice computation of the Isgur-Wise functions tau₁/₂ and tau₃/₂ at zero recoil. We consider three different light quark masses corresponding to 300 MeV < mPS < 450 MeV, which allow us to extrapolate our results to the physical u/d quark mass. We find tau₁/₂(1) = 0.296(26) and tau₃/₂(1) = 0.526(23). Uraltsev's sum rule is saturated up to 80% by the ground state. We discuss implications regarding semileptonic decays B --> Xc l nu and the associated "1/2 versus 3/2" puzzle.