On the set of atoms and strong atoms in additive monoids of cyclic semidomains

Abstract

Let $M$ be a cancellative and commutative monoid. A non-invertible element of $M$ is called an atom (or irreducible element) if it cannot be factored into two non-invertible elements, while an atom $a$ of $M$ is called strong if $a^n$ has a unique factorization in $M$ for every $n\in \mathbb{N}$. The monoid $M$ is atomic if every non-invertible element factors into finitely many atoms (repetitions allowed). For an algebraic number $\alpha$, we let $M_{\alpha }$ denote the additive monoid of the subsemiring ${\mathbb{N}}_0[\alpha ]$ of $\mathbb{C}$. The atomic structure of $M_{\alpha }$ reflects intricate interactions between algebraic number theory and additive semigroup theory. For $m,n\in {\mathbb{N}}_0\cup \{\infty \}$ (with $m\le n$), the pair $(m,n)$ is called realizable if there exists an algebraic number $\alpha \in \mathbb{C}$ such that $M_{\alpha }$ has $m$ strong atoms and $n$ atoms. Our primary goal is to identify classes of realizable pairs with the long-term goal of providing a complete description of the full set of realizable pairs.

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