Non-finitely generated monoids corresponding to finitely generated homogeneous subalgebras

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 , … , 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.