Non-finitely generated monoids corresponding to finitely generated homogeneous subalgebras

Abstract

The goal of this paper is to study the possible monoids appearing as the associated monoids of the initial algebra of a finitely generated homogeneous $k$-subalgebra of a polynomial ring $k[x_1,\dots ,x_n]$. Clearly, any affine monoid can be realized since the initial algebra of the affine monoid $k$-algebra is itself. On the other hand, the initial algebra of a finitely generated homogeneous $k$-algebra is not necessarily finitely generated. In this paper, we provide a new family of non-finitely generated monoids which can be realized as the initial algebras of finitely generated homogeneous $k$-algebras. Moreover, we also provide an example of a non-finitely generated monoid which cannot be realized as the initial algebra of any finitely generated homogeneous $k$-algebra.