$B!to!D^{(*)}ell u$ form factors from lattice QCD with relativistic heavy quarks

We report on our calculation of the B to D^(*) ell u form factors in 2+1 flavor lattice QCD. The Mobius domain-wall action is employed for light, strange, charm and bottom quarks. At lattice cutoffs 1/a sim 2.4, 3.6 and 4.5 GeV, we simulate bottom quark masses up to 0.7/a to control discretization errors. The pion mass is as low as 230 MeV. We extrapolate the form factors to the continuum limit and physical quark masses, and make a comparison with recent phenomenological analyses.