English

Bigraded components of F-finite F-modules

Commutative Algebra 2025-08-22 v1

Abstract

Let AA be a regular ring containing a field of characteristic p>0p>0 and let R=A[x1,,xm,y1,,yn]R=A[x_1,\ldots,x_m,y_1,\ldots,y_n] be standard bigraded over AA, i.e., bideg(A)=(0,0)\operatorname{bideg}(A)=(0,0), bideg(xi)=(1,0)\operatorname{bideg}(x_i)=(1,0) and bideg(yj)=(0,1)\operatorname{bideg}(y_j)=(0,1) for all ii and jj. Assume that M=i,jM(i,j)M=\bigoplus_{i,j} M_{(i,j)} is a bigraded FRF_R-finite, FRF_R-module. We use Lyubeznik's theory of FF-finite, FF-modules from \cite{Lyu-Fmod} to study the bigraded components of MM. The properties we study include vanishing, rigidity, Bass numbers, associated primes, and injective dimension of the components of MM. As an application we show that if (A,m)(A,\mathfrak{m}) is regular local ring containing a field of characteristic p>0p>0, R/IR/I is equidimensional, Bproj(R/I)\operatorname{Bproj}(R/I) is Cohen-Macaulay and non-empty, then HIj(R)(m,n)=0H^j_I(R)_{(m,n)}=0 for all (m,n)(0,0)(m,n)\geq (0,0) and all j>heightIj>\operatorname{height} I.

Keywords

Cite

@article{arxiv.2508.15742,
  title  = {Bigraded components of F-finite F-modules},
  author = {Sayed Sadiqul Islam and Tony J. Puthenpurakal},
  journal= {arXiv preprint arXiv:2508.15742},
  year   = {2025}
}

Comments

36 pages, comments welcome