On the maximal cross number of unique factorization indexed multisets

Abstract

In this paper, we study a conjecture of Gao and Wang concerning a proposed formula $K_1^*(G)$ for the maximal cross number $K_1(G)$ taken over all unique factorization indexed multisets over a given finite abelian group $G$. As a corollary of our first main result, we verify the conjecture for abelian groups of the form $C_{p^m}\oplus C_p, C_{p^m}\oplus C_q, C_{p^m}\oplus C_q^2$, $C_{p^m}\oplus C_r^n$ where $p,q$ are distinct primes and $r\in\{2,3\}$. In our second main result we verify that $K_1(G) = K_1^*(G)$ for groups of the form $C_r\oplus C_{p^m}\oplus C_p, C_{rp^mq}$ and $C_r\oplus C_p \oplus C_q^2$ for $r \in \{2,3\}$ given some restrictions on $p$ and $q$. We also study general techniques for computing and bounding $K_1(G)$, and derive an asymptotic result which shows that $K_1(G)$ becomes arbitrarily close to $K_1^*(G)$ as the smallest prime dividing $|G|$ goes to infinity, given certain conditions on the structure of $G$. We also derive some necessary properties of the structure of unique factorization indexed multisets which would hypothetically violate $k(S) \le K_1^*(G)$.