English

On lengths of modules over certain Artinian complete intersections

Commutative Algebra 2025-06-13 v1

Abstract

Let (Q,n)(Q,\mathfrak{n}) be a regular local ring of dimension c2c \geq 2 with algebraically closed residue field k=Q/nk = Q/\mathfrak{n}. Let f1,f2,fc1,gf_1, f_2, \ldots f_{c-1}, g be a regular sequence in QQ such that fin2 f_i \in \mathfrak{n}^2 for all ii and gng \in \mathfrak{n}. Set A=Q/(f1,,fc1,gr)A = Q/(f_1,\ldots, f_{c-1}, g^r) with r2r \geq 2. Notice AA is an Artinian complete intersection of codimension cc. We show that there exists αAPc1(k)\alpha_A \in \mathbb{P}^{c-1}(k) such that there exists integer mA2m_A \geq 2 (depending only on AA) with mAm_A dividing (M)\ell(M) for every finitely generated AA-module MM with αAV(M)\alpha_A \notin \mathcal{V}(M) (here (M)\ell(M) denotes the length of MM and V(M)\mathcal{V}(M) denotes the support variety of MM). As an application we prove that if kk be a field and R=k[X1,,Xc]/(X1a1,,Xcac)R = k[X_1, \ldots, X_c]/(X_1^{a_1}, \ldots, X_c^{a_c}) with ai2a_i \geq 2 and c2c \geq 2. Let pp be a prime number and assume pp divides two of the aia_i. Then pp divides (E)\ell(E) for any AA-module with bounded betti numbers.

Keywords

Cite

@article{arxiv.2506.10368,
  title  = {On lengths of modules over certain Artinian complete intersections},
  author = {Tony J. Puthenpurakal},
  journal= {arXiv preprint arXiv:2506.10368},
  year   = {2025}
}

Comments

arXiv admin note: substantial text overlap with arXiv:2307.16132

R2 v1 2026-07-01T03:12:34.837Z