## Equivalence between a massive spinning particle in Minkowski space and a massless one in a de Sitter space

It is shown that a free massive relativistic particle can be described by a both scale- and reparametrization-invariant action with a global de Sitter symmetry. The massive particle is one gauge choice. Another gauge choice of the same theory yields a massless particle in a de Sitter space. We supersymmetrize this theory by means of the superspace technique and show that the resulting theory has the corresponding properties for the classical spinning particle. We quantize this theory and show that we either get the ordinary massive Dirac equation or the generalized massless equation in a de Sitter space.