Some aspects of transversity

The specificities of transverse polarization with respect to helicity of ultrarelativistic fermions are pointed out. For massless fermions, a covariant transversity four-vector is defined, up to a kind of gauge transformation. The tranversity distribution of quarks in a nucleon is defined. Its possible connection to the magnetic or electric dipole moment of the baryon is conjectured. Consequences of the approximate chiral invariance on transverse spin asymmetries in hard processes are enumerated. The "sheared jet effect" introduced by Collins for measuring the transverse polarization of a final quark is presented.