Jucys–Murphy Elements and Unitary Matrix Integrals

In this paper, we study the relationship between polynomial integrals on the unitary group and the conjugacy class expansion of symmetric functions in Jucys–Murphy elements. Our main result is an explicit formula for the top coefficients in the class expansion of monomial symmetric functions in Jucys–Murphy elements, from which we recover the first-order asymptotics of polynomial integrals over U(N) as
$N\rightarrow\infty$
. Our results on class expansion include an analog of Macdonald’s result for the top connection coefficients of the class algebra, a generalization of Stanley and Olshanski’s result on the polynomiality of content statistics on Plancherel-random partitions, and an exact formula for the multiplicity of the class of full cycles in the expansion of a complete symmetric function in Jucys–Murphy elements. The latter leads to a new combinatorial interpretation of the Carlitz–Riordan central factorial numbers.