S_4-symmetry of 6j-symbols and Frobenius-Schur indicators in rigid   monoidal C^*-categories
  We show that a left-rigid monoidal C^*-category with irreducible monoidal unit is also a sovereign and spherical category. Defining a Frobenius-Schur type indicator we obtain selection rules for the fusion coefficients of irreducible objects. As a main result we prove S_4-invariance of 6j-symbols in such a category. 
J. Fuchs, A.Ch. Ganchev, K. Szlachanyi, P. Vecsernyes