Two-spinor description of massive particles and relativistic spin projection operators

On the basis of the Wigner unitary representations of the covering group ISL(2,C) of the Poincar\'{e} group, we obtain spin-tensor wave functions of free massive particles with arbitrary spin. The wave functions automatically satisfy the Dirac-Pauli-Fierz equations. In the framework of the two-spinor formalism we construct spin-vectors of polarizations and obtain conditions that fix the corresponding relativistic spin projection operators (Behrends-Fronsdal projection operators). With the help of these conditions we find explicit expressions for relativistic spin projection operators for integer spins (Behrends-Fronsdal projection operators) and then find relativistic spin projection operators for half integer spins. These projection operators determine the nominators in the propagators of fields of relativistic particles. We deduce generalizations of the Behrends-Fronsdal projection operators for arbitrary space-time dimensions D>2.Comment: 34 page

Generalization of the Bargmann-Wigner construction for infinite spin fields

We develop a generalization of the Wigner scheme for constructing the relativistic fields corresponding to irreducible representations of the four-dimensional Poincar\'{e} group with infinite spin. The fields are parameterized by a vector and an additional commuting vector or spinor variable. The equations of motion for fields of infinite spin are derived in both formulations under consideration.Comment: 1+29 pages, v2: typos correcte