Thermodynamics of Bose-Einstein condensation of relativistic gas
  We show that the free relativistic wave equation which describes the particle without or with rest mass has more than one part of energy spectrum. One part of energy spectrum is beginning with rest energy and it is not limited by above. This part of spectrum is called by us as normal. Another part of energy spectrum is beginning with the zero energy . This part of spectrum is called by us as anomalous since the zero energy corresponds to the infinite group velocity.The presence of the zero in the energy spectrum permits to consider the Bose-Einstein condensation. We show that the heat capasity has the finite discontinuity at the condensation temperature. The last means that we have the phase transition at the condensation point. 
A.Borghardt and D.Karpenko