Factorization in exclusive and semi-inclusive heavy flavor decays and effective theories for massless particles

We prove factorization in the semi-inclusive decay B --> D(*) + jet using the Large Energy Effective Theory (LEET). It is also shown that the LEET is unable to consistently describe exclusive processes, such as the decay B --> D(*) + pi(rho), and therefore also related properties such as factorization. The reason is an oversimplification of transverse momentum dynamics. We present a variant of the LEET, i.e. a new effective theory for massless particles, the <(LEET)over bar>, which properly takes into account transverse momentum dynamics and is the natural framework to study exclusive nonleptonic decays. The transition from the LEET to the <(LEET)over bar> is analogous to the replacement of geometrical optics with physical optics, the latter taking into account diffraction to a first approximation. A qualitative argument is presented in favor of factorization in the exclusive nonleptonic decays using the <(LEET)over bar>. Finally, it is shown that the collinear instability of the LEFT disappears when semi-inclusive observables are considered.