The Diophantine problem in finitely generated commutative rings (2012.09787v3)

Abstract: We study systems of polynomial equations in infinite finitely generated commutative associative rings with an identity element. For each such ring $R$ we obtain an interpretation by systems of equations of a ring of integers $O$ of a finite field extension of either $\mathbb{Q}$ or $\mathbb{F}_p(t)$, for some prime $p$ and variable $t$. This implies that the Diophantine problem (decidability of systems of polynomial equations) in $O$ is reducible to the same problem in $R$. If, in particular, $R$ has positive characteristic or, more generally, if $R$ has infinite rank, then we further obtain an interpretation by systems of equations of the ring $\mathbb{F}_p[t]$ in $R$. This implies that the Diophantine problem in $R$ is undecidable in this case. In the remaining case where $R$ has finite rank and zero characteristic, we see that $O$ is a ring of algebraic integers, and then the long-standing conjecture that $\mathbb{Z}$ is always interpretable by systems of equations in a ring of algebraic integers carries over to $R$. If true, it implies that the Diophantine problem in $R$ is also undecidable. Thus, in this case the Diophantine problem in every infinite finitely generated commutative unitary ring is undecidable. The present is the first in a series of papers were we study the Diophantine problem in different types of rings and algebras.