English

Stanley depth of the integral closure of monomial ideals

Commutative Algebra 2012-11-20 v3 Combinatorics

Abstract

Let II be a monomial ideal in the polynomial ring S=K[x1,...,xn]S=\mathbb{K}[x_1,...,x_n]. We study the Stanley depth of the integral closure Iˉ\bar{I} of II. We prove that for every integer k1k\geq 1, the inequalities sdepth(S/Ikˉ)sdepth(S/Iˉ){\rm sdepth} (S/\bar{I^k}) \leq {\rm sdepth} (S/\bar{I}) and sdepth(Ikˉ)sdepth(Iˉ){\rm sdepth} (\bar{I^k}) \leq {\rm sdepth} (\bar{I}) hold. We also prove that for every monomial ideal ISI\subset S there exist integers k1,k21k_1,k_2\geq 1, such that for every s1s\geq 1, the inequalities sdepth(S/Isk1)sdepth(S/Iˉ){\rm sdepth} (S/I^{sk_1}) \leq {\rm sdepth} (S/\bar{I}) and sdepth(Isk2)sdepth(Iˉ){\rm sdepth} (I^{sk_2}) \leq {\rm sdepth} (\bar{I}) hold. In particular, mink{sdepth(S/Ik)}sdepth(S/Iˉ)\min_k \{{\rm sdepth} (S/I^k)\} \leq {\rm sdepth} (S/\bar{I}) and mink{sdepth(Ik)}sdepth(Iˉ)\min_k \{{\rm sdepth} (I^k)\} \leq {\rm sdepth} (\bar{I}). We conjecture that for every integrally closed monomial ideal II, the inequalities sdepth(S/I)n(I){\rm sdepth}(S/I)\geq n-\ell(I) and sdepth(I)n(I)+1{\rm sdepth} (I)\geq n-\ell(I)+1 hold, where (I)\ell(I) is the analytic spread of II. Assuming the conjecture is true, it follows together with the Burch's inequality that Stanley's conjecture holds for IkI^k and S/IkS/I^k for k0k\gg 0, provided that II is a normal ideal.

Keywords

Cite

@article{arxiv.1205.6971,
  title  = {Stanley depth of the integral closure of monomial ideals},
  author = {S. A. Seyed Fakhari},
  journal= {arXiv preprint arXiv:1205.6971},
  year   = {2012}
}