English

On derived functors of Graded local cohomology modules

Commutative Algebra 2019-10-09 v2

Abstract

Let KK be a field of characteristic zero and let R=K[X1,,Xn]R=K[X_1, \ldots,X_n ], with standard grading. Let m=(X1,,Xn)\mathfrak{m}= (X_1, \ldots, X_n) and let EE be the ^*injective hull of R/m.R/\mathfrak{m}. Let An(K)A_n(K) be the nthn^{th} Weyl algebra over KK. Let I,JI, J be homogeneous ideals in RR. Fix i,j0i,j \geq 0 and set M=HIi(R)M = H^i_I(R) and N=HJj(R)N = H^j_J(R) considered as left An(K)A_n(K)-modules. We show the following two results for which no analogous result is known in charactersitc p>0p > 0. \begin{enumerate} Hml(\TorνR(M,N))E(n)al,νH^l_\mathfrak{m}(\Tor^R_\nu(M, N)) \cong E(n)^{a_{l,\nu}} for some al,ν0a_{l,\nu} \geq 0. For all ν0\nu \geq 0; the finite dimensional vector space \TorνAn(K)(M,N)\Tor^{A_n(K)}_\nu( M^\sharp, N) is concentrated in degree n-n (here MM^\sharp is the standard right An(K)A_n(K)-module associated to MM). \end{enumerate} We also conjecture that for all i0i \geq 0 the finite dimensional vector space \ExtAn(K)i(M,N)\Ext^i_{A_n(K)}(M, N) is concentrated in degree zero. We give a few examples which support this conjecture.

Keywords

Cite

@article{arxiv.1612.02968,
  title  = {On derived functors of Graded local cohomology modules},
  author = {Tony J. Puthenpurakal and Jyoti Singh},
  journal= {arXiv preprint arXiv:1612.02968},
  year   = {2019}
}

Comments

Mant typo's corrected