Probing new physics with (B)over-bar → ρ(770)l-(ν)over-barl and (B)over-bar → a1(1260)l-(ν)over-barl

The B meson semileptonic modes to rho(770) and a(1)(1260) are useful to pin down possible non-Standard Model effects. The four-dimensional differential (B) over bar -> rho(pi pi)l(-)(nu) over bar (l) and B -> a(1) (rho pi)l(-)(nu) over bar (l) decay distributions are computed in the Standard Model and in extensions involving new lepton-flavor universality violating semileptonic b -> u operators. The large energy limit for the light meson is also considered for both modes. The new effective couplings are constrained using the available data, and several observables in (B) over bar -> rho(pi pi)l(-)(nu) over bar (l) in which new physics effects can be better identified are selected, using the angular coefficient functions. The complementary role of (B) over bar -> rho(pi pi)l(-)(nu) over bar (l) and (B) over bar -> a(1)(rho pi)l(-)(nu) over bar (l) is discussed.