Lorentz symmetry and the internal structure of the nucleon

To investigate the internal structure of the nucleon, it is useful to introduce quantities that do not transform properly under Lorentz symmetry, such as the four-momentum of the quarks in the nucleon, the amount of the nucleon spin contributed by quark spin, etc. In this paper, we discuss to what extent these quantities provide Lorentz-invariant descriptions of the nucleon structure. copyright 1998 The American Physical Society