Properties of Polarization Density Matrix in Regge-Pole Models

We study two-body (or quasi-two-body) parity-conserving reactions with unpolarized beam and target. From the general considerations of angular momentum and parity conservation we derive the structure of the density matrices of the final particles. This structure becomes conspicuous when one uses transversity quantization with a special reordering for the lines and columns. We study the predictions of a single Regge trajectory exchange model. We derive the consequences of reality and factorization of residue functions, and of parity conservation at each vertex. The results are summarized in two tables. For the cases of low-spin particles we give these results in a geometrical form. As an example we plot some experimental data on $Q$-meson polarization.