Uniform semiclassical approximation for the Wigner 6j-symbol in terms of rotation matrices.

A new uniform asymptotic approximation for the Wigner 6j-symbol is given in terms of Wigner rotation matrices (d-matrices). The approximation is uniform in the sense that it applies for all values of the quantum numbers, even those near caustics. The derivation of the new approximation is not given, but the geometrical ideas supporting it are discussed and numerical tests are presented, including comparisons with the exact 6j-symbol and with the Ponzano-Regge approximation.