Connectedness of square-free Groebner deformations

Abstract

Let I ⊆ S = K [ x 1 , … , x n ] I\subseteq S=K[x_1,\ldots ,x_n] be a homogeneous ideal equipped with a monomial order > > . We show that if in > ⁡ ( I ) \operatorname {in}_{>}(I) is a square-free monomial ideal, then S / I S/I and S / in > ⁡ ( I ) S/\operatorname {in}_>(I) have the same connectedness dimension. We also show that graphs related to connectedness of these quotient rings have the same number of components. We also provide consequences regarding Lyubeznik numbers. We obtain these results by furthering the study of connectedness modulo a parameter in a local ring.