Transverse-Momentum Distributions and Spherical Symmetry
  Transverse-momentum dependent parton distributions (TMDs) are studied in the framework of quark models. In particular, quark model relations among TMDs are reviewed and their physical origin is discussed in terms of rotational-symmetry properties of the nucleon state in its rest frame. 
Cedric Lorce (Mainz U., Inst. Kernphys.) and Barbara Pasquini (Pavia   U. & INFN, Pavia)
hep-ph