A pr 2 00 3 LPT Orsay 03 - 19 B → π and B → K transitions in partially quenched chiral perturbation theory

We study the properties of the B → π and B → K transition form factors in partially quenched QCD by using the approach of partially quenched chiral perturbation theory combined with the static heavy quark limit. We show that the form factors change almost linearly when varying the value of the sea quark mass, whereas the dependence on the valence quark mass contains both the standard and chirally divergent (quenched) logarithms. A simple strategy for the chiral extrapolations in the lattice studies with Nsea = 2 is suggested. It consists of the linear extrapolations from the realistically accessible quark masses, first in the sea and then in the valence quark mass. The uncertainty induced by such an extrapolations is expected to be within 5% level. PACS: 12.39.Fe (Chiral Lagrangians), 12.39.Hg (Heavy quark effective theory), 13.20.-v (Leptonic and semileptonic decays of mesons), 11.15.Ha (Lattice gauge theory). ∗Unité mixte de Recherche du CNRS UMR 8627.