scholarly journals Interval Pattern Avoidance for Arbitrary Root Systems

2010 ◽  
Vol 53 (4) ◽  
pp. 757-762 ◽  
Author(s):  
Alexander Woo
Keyword(s):  
Root Systems ◽  
Pattern Avoidance ◽  
Weyl Groups ◽  
Schubert Varieties ◽  
Local Properties ◽  
Definition Of

AbstractWe extend the idea of interval pattern avoidance defined by Yong and the author for Sn to arbitrary Weyl groups using the definition of pattern avoidance due to Billey and Braden, and Billey and Postnikov. We show that, as previously shown by Yong and the author for GLn, interval pattern avoidance is a universal tool for characterizing which Schubert varieties have certain local properties, and where these local properties hold.

scholarly journals Deodhar Elements in Kazhdan-Lusztig Theory

2008 ◽  
Vol DMTCS Proceedings vol. AJ,... (Proceedings) ◽  
Author(s):  
Brant Jones
Keyword(s):  
Coxeter Groups ◽  
Pattern Avoidance ◽  
Weyl Groups ◽  
Schubert Varieties ◽  
Combinatorial Formula ◽  
Nous Obtenons ◽  
Integer Coefficients ◽  
Nous Montrons ◽  
International Audience ◽  
Lusztig Polynomials

International audience The Kazhdan-Lusztig polynomials for finite Weyl groups arise in representation theory as well as the geometry of Schubert varieties. It was proved very soon after their introduction that they have nonnegative integer coefficients, but no simple all positive interpretation for them is known in general. Deodhar has given a framework, which generally involves recursion, to express the Kazhdan-Lusztig polynomials in a very attractive form. We use a new kind of pattern-avoidance that can be defined for general Coxeter groups to characterize when Deodhar's algorithm yields a non-recursive combinatorial formula for Kazhdan-Lusztig polynomials $P_{x,w}(q)$ of finite Weyl groups. This generalizes results of Billey-Warrington which identified the $321$-hexagon-avoiding permutations, and Fan-Green which identified the fully-tight Coxeter groups. We also show that the leading coefficient known as $\mu (x,w)$ for these Kazhdan―Lusztig polynomials is always either $0$ or $1$. Finally, we generalize the simple combinatorial formula for the Kazhdan―Lusztig polynomials of the $321$-hexagon-avoiding permutations to the case when $w$ is hexagon avoiding and maximally clustered. Les polynômes de Kazhdan-Lusztig $P_{x,w}(q)$ des groupes de Weyl finis apparaissent en théorie des représentations, ainsi qu’en géométrie des variétés de Schubert. Il a été démontré peu après leur introduction qu’ils avaient des coefficients entiers positifs, mais on ne connaît toujours pas d’interprétation combinatoire simple de cette propriété dans le cas général. Deodhar a proposé un cadre donnant un algorithme, en général récursif, calculant des formules attractives pour les polynômes de Kazhdan-Lusztig. Billey-Warrington ont démontré que cet algorithme est non récursif lorsque$w$ évite les hexagones et les $321$ et qu’il donne des formules combinatoires simples. Nous introduisons une notion d’évitement de schémas dansles groupes de Coxeter quelconques nous permettant de généraliser les résultats de Billey-Warrington à tout groupe de Weyl fini. Nous montrons que le coefficient de tête $\mu (x,w)$ de ces polynômes de Kazhdan-Lusztig est toujours $0$ ou $1$. Cela généralise aussi des résultats de Fan-Greenqui identifient les groupes de Coxeter complètement serrés. Enfin, en type $A$, nous obtenons une classe plus large de permutations évitant la récursion.

scholarly journals The Tutte polynomial of symmetric hyperplane arrangements

2020 ◽  
Vol 29 (03) ◽  
pp. 2050004
Author(s):  
Hery Randriamaro
Keyword(s):  
Hyperplane Arrangement ◽  
Dual Graph ◽  
Tutte Polynomial ◽  
Hyperplane Arrangements ◽  
Weyl Groups ◽  
Reflection Groups ◽  
Tutte Polynomials ◽  
One Year ◽  
The One ◽  
Definition Of

The Tutte polynomial is originally a bivariate polynomial which enumerates the colorings of a graph and of its dual graph. Ardila extended in 2007 the definition of the Tutte polynomial on the real hyperplane arrangements. He particularly computed the Tutte polynomials of the hyperplane arrangements associated to the classical Weyl groups. Those associated to the exceptional Weyl groups were computed by De Concini and Procesi one year later. This paper has two objectives: On the one side, we extend the Tutte polynomial computing to the complex hyperplane arrangements. On the other side, we introduce a wider class of hyperplane arrangements which is that of the symmetric hyperplane arrangements. Computing the Tutte polynomial of a symmetric hyperplane arrangement permits us to deduce the Tutte polynomials of some hyperplane arrangements, particularly of those associated to the imprimitive reflection groups.

scholarly journals Zeta-functions of root systems and Poincaré polynomials of Weyl groups

2020 ◽  
Vol 72 (1) ◽  
pp. 87-126
Author(s):  
Yasushi Komori ◽  
Kohji Matsumoto ◽  
Hirofumi Tsumura
Keyword(s):  
Zeta Functions ◽  
Root Systems ◽  
Weyl Groups

INVERSIONS IN CLASSICAL WEYL GROUPS

2007 ◽  
Vol 09 (01) ◽  
pp. 1-20
Author(s):  
KEQUAN DING ◽  
SIYE WU
Keyword(s):  
Finite Group ◽  
Weyl Group ◽  
Root Systems ◽  
Flag Manifold ◽  
Length Function ◽  
Weyl Groups ◽  
Flag Manifolds ◽  
A Finite Group

We introduce inversions for classical Weyl group elements and relate them, by counting, to the length function, root systems and Schubert cells in flag manifolds. Special inversions are those that only change signs in the Weyl groups of types Bn, Cnand Dn. Their counting is related to the (only) generator of the Weyl group that changes signs, to the corresponding roots, and to a special subvariety in the flag manifold fixed by a finite group.

scholarly journals On flag varieties, hyperplane complements and Springer representations of Weyl groups

1990 ◽  
Vol 49 (3) ◽  
pp. 449-485 ◽  
Author(s):  
G. I. Lehrer ◽  
T. Shoji
Keyword(s):  
Algebraic Group ◽  
Weyl Group ◽  
Nilpotent Element ◽  
Parabolic Type ◽  
Linear Algebraic Group ◽  
Weyl Groups ◽  
Complex Numbers ◽  
Flag Varieties ◽  
Group Representations ◽  
Definition Of

AbstractLet G be a connected reductive linear algebraic group over the complex numbers. For any element A of the Lie algebra of G, there is an action of the Weyl group W on the cohomology Hi(BA) of the subvariety BA (see below for the definition) of the flag variety of G. We study this action and prove an inequality for the multiplicity of the Weyl group representations which occur ((4.8) below). This involves geometric data. This inequality is applied to determine the multiplicity of the reflection representation of W when A is a nilpotent element of “parabolic type”. In particular this multiplicity is related to the geometry of the corresponding hyperplane complement.

scholarly journals Tachyons and Preferred Frames

1997 ◽  
Vol 12 (09) ◽  
pp. 1677-1709 ◽  
Author(s):  
Jakub Rembieliński
Keyword(s):  
Field Theory ◽  
Inertial Frame ◽  
Lorentz Symmetry ◽  
Spontaneous Breaking ◽  
Neutrino Masses ◽  
Relativity Principle ◽  
Consistent Field ◽  
Local Properties ◽  
Definition Of ◽  
Synchronization Procedure

Quantum field theory of spacelike particles is investigated in the framework of an absolute causality scheme preserving Lorentz symmetry. It is related to an appropriate choice of the synchronization procedure (definition of time). In this formulation existence of field excitations (tachyons) distinguishes an inertial frame (privileged frame of reference) via spontaneous breaking of the so-called synchronization group. In this scheme the relativity principle is broken but Lorentz symmetry is exactly preserved in agreement with local properties of the observed world. It is shown that tachyons are associated with unitary orbits of Poincaré mappings induced from the SO(2) little group instead of the SO(2,1) one. Therefore the corresponding elementary states are labeled by helicity. The cases of the helicity λ = 0 and [Formula: see text] are investigated in detail and a corresponding consistent field theory is proposed. In particular, it is shown that the Dirac-like equation proposed by Chodos et al.,1 inconsistent in the standard formulation of QFT, can be consistently quantized in the presented framework. This allows us to treat more seriously the possibility that neutrinos might be fermionic tachyons, as is suggested by experimental data about neutrino masses.2–4

scholarly journals QUASI ROOT SYSTEMS AND VERTEX OPERATOR REALIZATIONS OF THE VIRASORO ALGEBRA

2013 ◽  
Vol 12 (07) ◽  
pp. 1350028
Author(s):  
BORIS NOYVERT
Keyword(s):  
Lie Algebras ◽  
Virasoro Algebra ◽  
Root Systems ◽  
Vertex Operators ◽  
Boson Fields ◽  
Dimension 2 ◽  
Definition Of ◽  
Extensive List ◽  
Scaling Dimension ◽  
Natural Way

A construction of the Virasoro algebra in terms of free massless two-dimensional boson fields is studied. The ansatz for the Virasoro field contains the most general unitary scaling dimension 2 expression built from vertex operators. The ansatz leads in a natural way to a concept of a quasi root systems. This is a new notion generalizing the notion of a root system in the theory of Lie algebras. We introduce a definition of a quasi root systems and provide an extensive list of examples. Explicit solutions of the ansatz are presented for a range of quasi root systems.

scholarly journals The Garnir Relations for Weyl Groups of Type $C_n$

10.37236/797 ◽  
2008 ◽  
Vol 15 (1) ◽  
Author(s):  
Himmet Can
Keyword(s):  
Symmetric Groups ◽  
Root Systems ◽  
Weyl Groups ◽  
Specht Modules ◽  
Combinatorial Description ◽  
Combinatorial Constructions

The Garnir relations play a very important role in giving combinatorial constructions of representations of the symmetric groups. For the Weyl groups of type $C_n$, having obtained the alternacy relation, we give an explicit combinatorial description of the Garnir relation associated with a $\Delta$-tableau in terms of root systems. We then use these relations to find a $K$-basis for the Specht modules of the Weyl groups of type $C_n$.

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