Complete Positivity of Comultiplication and Primary Criteria for Unitary Categorification

In this paper, we investigate quantum Fourier analysis on subfactors and unitary fusion categories. We prove the complete positivity of the comultiplication for subfactors and derive a primary $n$-criterion of unitary categorification of multifusion rings. It is stronger than the Schur product criterion when $n\geq 3$. The primary criterion could be transformed into various criteria, which are easier to check in practice even for noncommutative, high-rank, high-multiplicity, multifusion rings. More importantly, the primary criterion could be localized on a sparse set, so that it works for multifusion rings with sparse known data. We give numerous examples to illustrate the efficiency and the power of these criteria.