Time Reversal Induces Negative Mass and Charge Conjugation: On the   Physical Interpretation of the Irreducible Unitary Representations of   Negative Mass and Energy of the Full Poincare Group
  This article proves that according to the principles of quantum mechanics the existence of elementary particles of negative mass is physically plausible. Heisenberg's uncertainty principle plays an important role in this demonstration. By reversing time, charge and mass are conjugated and the symmetry group is that of the Poincare with space-time reflections (full Poincare group). Particles that tunnel from the future time-like cone to the past time-like cone move backward in time with negative mass (and energy). These particles are interpreted as antiparticles of positive mass (and energy) that move forward in time. There is not a physical law that precludes two observers from seeing different mass signs of a particle, since the mass is not a Poincare invariant, but its square, p^2 = -m^2. 
Jose N. Pecina-Cruz