Lorentz invariant CPT violation: Particle and antiparticle mass   splitting
  The interpretation of neutrino oscillation data has led to the question whether, in principle, an antiparticle like antineutrino can have a different mass than its particle. In the framework of a Lorentz invariant CPT violation, which is based on the nonlocal interaction vertex and characterized by the infrared divergent form factor, we present an explicit Lagrangian model for the fermion and antifermion mass splitting. 
Masud Chaichian, Kazuo Fujikawa and Anca Tureanu
hep-th hep-ph