超相対論的極限
Dieckmann, M. E. (2005). “Particle simulation of an ultrarelativistic two-stream instability”. Phys. Rev. Lett. 94 (15): 155001. Bibcode: 2005PhRvL..94o5001D. doi:10.1103/PhysRevLett.94.155001. PMID 15904153.