The shape function in field theory

The shape function describes Fermi motion effects (non perturbative) in sem i-inclusive heavy flavor decay. Its renormalization properties are substant ially dependent on the kind of ultraviolet regulator used. For example, the double logarithm which appears at one loop is larger by a factor 2 in dime nsional regularization than in lattice regularization. We show that factori zation of long-distance effects in the shape function is achieved with any regulator considered.