Regularity and h-polynomials of toric ideals of graphs

Abstract

For all integers $4\le r\le d$, we show that there exists a finite simple graph $G=G_{r,d}$ with toric ideal $I_G\subset R$ such that $R/I_G$ has (Castelnuovo-Mumford) regularity $r$ and $h$-polynomial of degree $d$. To achieve this goal, we identify a family of graphs such that the graded Betti numbers of the associated toric ideal agree with its initial ideal, and furthermore, this initial ideal has linear quotients. As a corollary, we can recover a result of Hibi, Higashitani, Kimura, and O'Keefe that compares the depth and dimension of toric ideals of graphs.