  The effect of torsion in theories of quantum gravity is known to be well
described by an axion-like field which couples to matter as well as to
gravitation and radiation gauge fields. In this note we consider a particular
kind of torsion, arising from the Kalb-Ramond antisymmetric tensor field that
appears in the gravitational multiplet of string theory. We investigate the
implications for leptogenesis. It is shown that leptogenesis can occur even at
tree-level and with only one generation of right-handed Majorana neutrinos, due
to CP and CPT violation introduced by the background geometry.
