Rigidity of Bott-Samelson-Demazure-Hansen variety for $F_4$ and $G_2$

Abstract

Let $G$ be a simple algebraic group of adjoint type over $\mathbb{C},$ whose root system is of type $F_4.$ Let $T$ be a maximal torus of $G$ and $B$ be a Borel subgroup of $G$ containing $T.$ Let $w$ be an element of Weyl group $W$ and $X(w)$ be the Schubert variety in the flag variety $G/B$ corresponding to $w.$ Let $Z(w,\underline{i})$ be the Bott-Samelson-Demazure-Hansen variety (the desingularization of $X(w)$) corresponding to a reduced expression $\underline{i}$ of $w.$ In this article, we study the cohomology modules of the tangent bundle on $Z(w_0,\underline{i}),$ where $w_0$ is the longest element of the Weyl group $W.$ We describe all the reduced expressions of $w_0$ in terms of a Coxeter element such that $Z(w_0,\underline{i})$ is rigid (see Theorem 8.1). Further, if $G$ is of type $G_2,$ there is no reduced expression $\underline{i}$ of $w_0$ for which $Z(w_0,\underline{i})$ is rigid (see Theorem 8.2).

arXiv comment46 pages. arXiv admin note: text overlap with arXiv:1610.00812, arXiv:1908.05605

References in corpus (1)

• Rigidity of Bott-Samelson-Demazure-Hansen variety for $PSp(2n,\mathbb{C})$