Linearity defect of edge ideals and Fröberg's theorem

Abstract

Fröberg's classical theorem about edge ideals with $2$-linear resolution can be regarded as a classification of graphs whose edge ideals have linearity defect zero. Extending his theorem, we classify all graphs whose edge ideals have linearity defect at most $1$. Our characterization is independent of the characteristic of the base field: the graphs in question are exactly weakly chordal graphs with induced matching number at most $2$. The proof uses the theory of Betti splittings of monomial ideals due to Francisco, Hà, and Van Tuyl and the structure of weakly chordal graphs. Along the way, we compute the linearity defect of edge ideals of cycles and weakly chordal graphs. We are also able to recover and generalize previous results due to Dochtermann-Engström, Kimura, and Woodroofe on the projective dimension and Castelnuovo-Mumford regularity of edge ideals.

Final version, with minor corrections. To appear in J. Algebr. Combin

Cited by in corpus (2)

• Regularity and Koszul property of symbolic powers of monomial ideals
• Stable value of depth of symbolic powers of edge ideals of graphs