Periodic Occurance of Complete Intersection Monomial Curves

Abstract

We study the complete intersection property of monomial curves in the family $Γ_{å+ \jj} = {(t^{a_0 + j}, t^{a_1+j},..., t^{a_n + j}) ~ | ~ j \geq 0, ~ a_0 < a_1 <...< a_n}$. We prove that if $Γ_{å+\jj}$ is a complete intersection for $j\gg 0$, then $Γ_{å+\jj+\underline{a_n}}$ is a complete intersection for $j\gg 0$. This proves a conjecture of Herzog and Srinivasan on eventual periodicity of Betti numbers of semigroup rings under translations for complete intersections. We also show that if $Γ_{å+\jj}$ is a complete intersection for $j\gg 0$, then ${\Gamma }_{\mathring{a}}$ is a complete intersection. We also characterize the complete intersection property of this family when $n=3$.

12 pages, added a reference which was missing in the earlier version