English

On two conjectures of Murthy

Commutative Algebra 2017-12-18 v4

Abstract

This article concerns two conjectures of M. P. Murthy. For Murthy's conjecture on complete intersections, the major breakthrough has still been the result proved by Mohan Kumar in 1978. In this article we improve "Mohan Kumar's bound" when the base field is Fp\overline{\mathbb F}_p, and illustrate some applications of our result. Murthy's other conjecture is on a "splitting problem", which is roughly about finding the precise obstruction for a projective RR-module PP of rank dim(R)1\text{dim}(R)-1 to split off a free summand of rank one, where RR is a smooth affine algebra over an algebraically closed field kk. Asok-Fasel achieved the initial breakthrough, by settling it for 33-folds and 44-folds when char(k)2char(k)\neq 2. For k=Fpk=\overline{\mathbb F}_p (p2p\neq 2) and dim(R)5\text{dim}(R)\geq 5 we define an obstruction group and an obstruction class for PP (whose determinant is trivial). As application we obtain: PP splits if and only if it maps onto a complete intersection ideal of height dim(R)1\text{dim}(R)-1.

Keywords

Cite

@article{arxiv.1710.04281,
  title  = {On two conjectures of Murthy},
  author = {Mrinal Kanti Das},
  journal= {arXiv preprint arXiv:1710.04281},
  year   = {2017}
}

Comments

v1: To be ignored. v2: Completely revised and expanded (subsumes arXiv:1710.06853). v3: Example 3.6 is the only addition to v2. v4: fixed some typos and slips. Comments are welcome!

R2 v1 2026-06-22T22:10:47.304Z