Transverse momentum dependent gluon distribution and fragmentation functions

We investigate the twist two gluon distribution functions for spin-1/2 hadrons, emphasizing the intrinsic transverse momentum of the gluons. These functions are relevant in leading order in the inverse hard scale in scattering processes such as inclusive leptoproduction or Drell-Yan scattering, or more generally in hard processes in which at least two hadrons are involved. They show up in azimuthal asymmetries. For future estimates of such observables, we discuss specific bounds on these functions. ©2001 The American Physical Society.