Unification of Spacetime Symmetries of Massive and Massless Particles

Abstract

The internal space-time symmetries of relativistic particles are dictated by Wigner's little groups. The $O(3)$-like little group for a massive particle at rest and the $E(2)$-like little group of a massless particle are two different manifestations of the same covariant little group. Likewise, the quark model and parton pictures are two different manifestations of the one covariant entity.

7 pages,LaTeX,based on a talk presented at the 2nd German-Polish Symposium on New Ideas in the Theory of Fundamental Interactions (Zakopane, Poland, September 11-15, 1995)