SCET sum rules for heavy-to-light form factors

We consider a sum rule for heavy-to-light form factors in soft-collinear effective theory (SCET). Using the correlation function given by the time-ordered product of a heavy-to-light current and its hermitian conjugate, the heavy-to-light soft form factor zeta_P can be related to the leading-order B meson shape function. Using the scaling behavior of the heavy-to-light form factor in Lambda_QCD/m_b, we put a constraint on the behavior of the $B$ meson shape function near the endpoint. We employ the sum rule to estimate the size of zeta_P with the model for the shape function and find that it ranges from 0.01 to 0.07.