English

GIT quotient of Schubert varieties modulo one dimensional torus

Algebraic Geometry 2024-01-24 v1

Abstract

Let GG be a simple algebraic group of adjoint type of rank nn over C\mathbb{C}. Let TT be a maximal torus of GG, and BB be a Borel subgroup of GG containing TT. Let W=NG(T)/TW=N_{G}(T)/T be the Weyl group of GG. Let S={α1,,αn}S=\{\alpha_{1},\ldots,\alpha_{n}\} be the set of simple roots of GG relative to (B,T)(B,T). Let λs\lambda_{s} be the one parameter subgroup of TT dual to αs\alpha_{s}. In this paper, we give a criterion for Schubert varieties admitting semistable points for the λs\lambda_{s}-linearized line bundles L(χ)\mathcal{L}(\chi) associated to every dominant character χ\chi of TT. If ωr\omega_{r} is a minuscule fundamental weight and mωrX(T)m\omega_{r}\in X(T), then we prove that there is a unique minimal dimensional Schubert variety X(ws,r)X(w_{s,r}) in G/PS{αr}G/P_{S\setminus\{\alpha_{r}\}} such that X(ws,r)λsss(L(mωr))ϕX(w_{s,r})^{ss}_{\lambda_{s}}(\mathcal{L}(m\omega_{r}))\neq \phi. Further, we prove that if G=PSL(n,C)G=PSL(n,\mathbb{C}), and nrsn\nmid rs, m=n(rs,n)m=\frac{n}{(rs,n)}, and p=rsnp=\lfloor\frac{rs}{n}\rfloor then the GIT quotient of the minimal dimensional Schubert variety X(ws,r)X(w_{s,r}) is isomorphic to the projective space P(M(sp,rp))\mathbb{P}(M(s-p, r-p)), where M(sp,rp)M(s-p, r-p) is the (sp)×(rp)(s-p)\times (r-p)-matrices with complex numbers as entries.

Keywords

Cite

@article{arxiv.2401.12527,
  title  = {GIT quotient of Schubert varieties modulo one dimensional torus},
  author = {Arkadev Ghosh and S. S. Kannan},
  journal= {arXiv preprint arXiv:2401.12527},
  year   = {2024}
}

Comments

26 pages

R2 v1 2026-06-28T14:24:22.485Z