  Dirac's equation for a massless particle is conformal invariant, and
accordingly has an so(4,2)invariance algebra. It is known that although Dirac's
equation for a massive spin 1/2 particle is not conformal invariant, it too has
an so(4,2) invariance algebra. It is shown here that the algebra of operators
associated with a 4-component massless particle, or two flavors of 2-component
massless particles, can be deformed into the algebra of operators associated
with a spin 1/2 particle with positive rest mass. It is speculated that this
may be exploited to describe massless neutrino mixing.
