Betti numbers and degree bounds for some linked zero-schemes

Abstract

In [J. Herzog, H. Srinivasan, Bounds for multiplicities, Trans. Amer. Math. Soc. 350 (1998) 2879–2902], Herzog and Srinivasan study the relationship between the graded Betti numbers of a homogeneous ideal I in a polynomial ring R and the degree of I . For certain classes of ideals, they prove a bound on the degree in terms of the largest and smallest Betti numbers, generalizing results of Huneke and Miller in [C. Huneke, M. Miller, A note on the multiplicity of Cohen–Macaulay algebras with pure resolutions, Canad. J. Math. 37 (1985) 1149–1162]. The bound is conjectured to hold in general; we study this using linkage. If R / I is Cohen–Macaulay, we may reduce to the case where I defines a zero-dimensional subscheme Y . If Y is residual to a zero-scheme Z of a certain type (low degree or points in special position), then we show that the conjecture is true for I Y .