One open problem is the completion of the Bargmann–Wigner programme for the isometry group SO(D − 2, 1) of the de Sitter spacetime dS D −2. Ideally, the physical components of wave functions would be realized on the hyperboloid dS D −2 of radius μ > 0 embedded in R D − − 2 , 1 and the corresponding O(D −2, 1) covariant wave equations of the infinite-dimensional unitary representation to be known.