English

Abelian ideals and amazing roots

Representation Theory 2017-11-15 v1

Abstract

Let g\mathfrak g be a simple Lie algebra with a Borel subalgebra b\mathfrak b. To any long positive root γ\gamma, one associates two ideals of b\mathfrak b: the abelian ideal I(γ)maxI(\gamma)_{max} and not necessarily abelian ideal IγI\langle{\succcurlyeq}\gamma\rangle. It is known that I(γ)maxIγI(\gamma)_{max} \subset I\langle{\succcurlyeq}\gamma\rangle, and γ\gamma is said to be amazing if the equality holds. The set of amazing roots, A\mathcal A, is closed under the operation `\vee' in Δ+\Delta^+, and γA\gamma\in\mathcal A is said to be primitive, if it cannot be written as γ1γ2\gamma_1\vee\gamma_2 with incomparable amazing roots γ1,γ2\gamma_1,\gamma_2. We classify the amazing roots and notice that the number of primitive roots equals rk(g)\mathsf{rk}(\mathfrak g). Moreover, if Π\Pi (resp. Apr\mathcal A_{\sf pr}) is the set of simple (resp. primitive) roots, then there is a natural bijection ΠApr\Pi\longleftrightarrow \mathcal A_{\sf pr}. We also describe the set AH\mathcal A\cap{\mathcal H}, where H{\mathcal H} is the Heisenberg subset of Δ+\Delta^+.

Keywords

Cite

@article{arxiv.1711.04129,
  title  = {Abelian ideals and amazing roots},
  author = {Dmitri I. Panyushev},
  journal= {arXiv preprint arXiv:1711.04129},
  year   = {2017}
}

Comments

9 pages, to appear in International J. of Mathematics

R2 v1 2026-06-22T22:42:57.191Z