Minimal partitions with a given $s$-core and $t$-core

Abstract

Suppose $s$ and $t$ are coprime positive integers, and let $\sigma$ be an $s$-core partition and $\tau$ a $t$-core partition. In this paper we consider the set ${\mathcal{P}}_{\sigma ,\tau }(n)$ of partitions of $n$ with $s$-core $\sigma$ and $t$-core $\tau$. We find the smallest $n$ for which this set is non-empty, and show that for this value of $n$ the partitions in ${\mathcal{P}}_{\sigma ,\tau }(n)$ (which we call $(\sigma ,\tau )$-minimal partitions) are in bijection with a certain class of $(0,1)$-matrices with $s$ rows and $t$ columns. We then use these results in considering conjugate partitions: we determine exactly when the set ${\mathcal{P}}_{\sigma ,\tau }(n)$ consists of a conjugate pair of partitions, and when ${\mathcal{P}}_{\sigma ,\tau }(n)$ contains a unique self-conjugate partition.