arXiv subjects

Patrick Polo

Publications and source records attributed to Patrick Polo.

5 recordsLinked to original sources

arXiv2026

On some components of $L(\rho)\otimes L(\rho)$ associated with rooted trees for symmetrizable Kac-Moody algebras

Let $\mathfrak{g}$ be a symmetrizable Kac-Moody algebra over $\mathbb{C}$ and let $L(\rho)$ be the irreducible integrable $\mathfrak{g}$-module with highest weight $\rho$. Let $I$ be a subgraph of the Dynkin diagram of $\mathfrak{g}$ which has only simple bonds and no cycle of length $\geq 3$. For every subset $D$ of $I$, denote by $\beta_D$ the sum of the simple roots corresponding to $D$. To every $D \subset I$ such that $\lambda_{D,I} = 2\rho - \beta_I - \beta_D$ is dominant, we associate certain elements $\pi_{D,I}$ of weight $\lambda_{D,I} {-} \rho$ in the crystal $B(\rho)$, which depend on the choice of a root vertex in each connected component of $I$. Then we prove that our elements are $\rho$-dominant elements of $B(\rho)$, hence provide new families of components of the tensor product $L(\rho)\otimes L(\rho)$.

math.RT↗

arXiv2025

Classification of the root systems $R(m)$

Let $R$ be a reduced irreducible root system, $h$ its Coxeter number and $m$ a positive integer smaller than $h$. Choose of base of $R$, whence a corresponding height function, and let $R(m)$ be the set of roots whose height is a multiple of $m$. In a recent paper, S. Nadimpalli, S. Pattanayak and D. Prasad studied, for the purposes of character theory at torsion elements, the root systems $R(m)$; in particular, they introduced a constant $d_m$ which is always the dimension of a representation of the semisimple, simply-connected group with root system dual to $R(m)$ and equals $1$ if the roots of height $m$ form a base of $R(m)$, and proved this property when $R$ is of type $A$ or $C$, and also in type $B$ if $m$ is odd. In this paper, we complete their analysis by determining a base of $R(m)$ and computing the constant $d_m$ in all cases.

math.RT↗

arXiv2019

On the cohomology of line bundles over certain flag schemes II

Over a field $K$ of characteristic $p$, let $Z$ be the incidence variety in $\mathbb{P}^d \times (\mathbb{P}^d)^*$ and let $\mathcal{L}$ be the restriction to $Z$ of the line bundle $\mathcal{O}(-n-d) \boxtimes \mathcal{O}(n)$, where $n = p+f$ with $0 \leq f \leq p-2$. We prove that $H^d(Z,\mathcal{L})$ is the simple $\operatorname{GL}_{d+1}$-module corresponding to the partition $\lambda_0 = (p-1+f,p-1,f+1)$. When $f= 0$, using the first author's description of $H^d(Z,\mathcal{L})$ and Jantzen's sum formula, we obtain as a by-product that the sum of the monomial symmetric functions $m_\lambda$, for all partitions $\lambda$ of $2p-1$ less than $(p-1,p-1,1)$ in the dominance order, is the alternating sum of the Schur functions $S_{p-1,p-1-i,1^{i+1}}$ for $i=0,\dots,p-2$.

math.RT↗

arXiv2003

Arrangements associated to chordal graphs and limits of colored braid groups

Let G be a chordal graph, X(G) the complement of the associated complex arrangement and Gamma(G) the fundamental group of X(G). We show that Gamma(G) is a limit of colored braid groups over the poset of simplices of G. When G = G_T is the comparability graph associated with a rooted tree T, a case recently investigated by the first author, the result takes the following very simple form: Gamma(G_T) is a limit over T of colored braid groups.

math.AT↗

arXiv1999

Large Schubert varieties

For a semisimple adjoint algebraic group $G$ and a Borel subgroup $B$, consider the double classes $BwB$ in $G$ and their closures in the canonical compactification of $G$: we call these closures large Schubert varieties. We show that these varieties are normal and Cohen-Macaulay; we describe their Picard group and the spaces of sections of their line bundles. As an application, we construct geometrically van der Kallen's filtration of the algebra of regular functions on $B$. We also construct a degeneration of the flag variety $G/B$ embedded diagonally in $G/B\times G/B$, into a union of Schubert varieties. This leads to formulae for the class of the diagonal in $T$-equivariant $K$-theory of $G/B\times G/B$, where $T$ is a maximal torus of $B$.

math.AG↗