Mean values of arithmetic functions in short intervals and in arithmetic progressions in the large-degree limit

Abstract: A classical problem in number theory is showing that the mean value of an arithmetic function is asymptotic to its mean value over a short interval or over an arithmetic progression, with the interval as short as possible or the modulus as large as possible. We study this problem in the function field setting, and prove for a wide class of arithmetic functions (namely factorization functions), that such an asymptotic result holds, allowing the size of the short interval to be as small as a square-root of the size of the full interval, and analogously for arithmetic progressions. For instance, our results apply for the indicator function of polynomials with a divisor of given degree, and are much stronger than those known for the analogous function over the integers. As opposed to many previous works, our results apply in the \emph{large-degree limit}, where the base field $\mathbb{F}_q$ is fixed. Our proofs are based on relationships between certain character sums and symmetric functions, and in particular we use results from symmetric function theory due to E\u{g}ecio\u{g}lu and Remmel. We also use recent bounds of Bhowmick, L^{e} and Liu on character sums, which are in the spirit of the Drinfeld--Vl\u{a}du\c{t} bound.