English

Graded components of local cohomology modules over polynomial rings

Commutative Algebra 2024-11-21 v1

Abstract

Let KK be a field and let R=K[X1,,Xm]R = K[X_1, \ldots, X_m] with m2m \geq 2. Give RR the standard grading. Let II be a homogeneous ideal of height gg. Assume 1gm11 \leq g \leq m -1. Suppose HIi(R)0H^i_I(R) \neq 0 for some i0i \geq 0. We show (1) HIi(R)n0H^i_I(R)_n \neq 0 for all nmn \leq -m. (2) if Supp HIi(R){(X1,,Xm)}H^i_I(R) \neq \{ (X_1, \ldots, X_m)\} then HIi(R)n0H^i_I(R)_n \neq 0 for all nZn \in \mathbb{Z}. Furthermore if char K=0K = 0 then dimKHIi(R)n\dim_K H^i_I(R)_n is infinite for all nZn \in \mathbb{Z}. (3) dimKHIg(R)n\dim_K H^g_I(R)_n is infinite for all nZn \in \mathbb{Z}. In fact we prove our results for T(R)\mathcal{T}(R) where T()\mathcal{T}(-) is a large sub class of graded Lyubeznik functors

Keywords

Cite

@article{arxiv.2411.13090,
  title  = {Graded components of local cohomology modules over polynomial rings},
  author = {Tony J. Puthenpurakal},
  journal= {arXiv preprint arXiv:2411.13090},
  year   = {2024}
}