Noncommutative factorizations of higher sine functions in positive characteristic

Abstract

In this paper we describe new noncommutative factorizations of functions related to $d$-th tensor powers of Carlitz's $\mathbb F_q[θ]$-module for $d\geq 1$, called higher sine functions. In recent work by the second author, factorizations of this type have been constructed for operators which are combinations of powers of a Frobenius endomorphism with coefficients ``in $\operatorname{End}(\operatorname{End}(\mathbb G_a^d))$''. In the present paper we succeed in determining factorizations with coefficients ``in $\operatorname{End}(\mathbb G_a^d)$'' which are not easily deducible from previous work. One key ingredient in obtaining this is an application of a ``motivic pairing'' that the first author introduced in recent work. Another key ingredient is the notion of ``$Δ$-matrix'' which comes into play in the analysis of the coefficients of the factorizations. Our results can be applied to explicitly describe analogues of shuffle $q^n$-powers for multiple polylogarithms at one, and to multiple zeta values of Thakur. All the identities we prove occur at the finite level.