English

A classification of sharp tridiagonal pairs

Rings and Algebras 2010-01-13 v1 Combinatorics

Abstract

Let FF denote a field and let VV denote a vector space over FF with finite positive dimension. We consider a pair of linear transformations A:VVA:V \to V and A:VVA^*:V \to V that satisfy the following conditions: (i) each of A,AA,A^* is diagonalizable; (ii) there exists an ordering {Vi}i=0d\lbrace V_i\rbrace_{i=0}^d of the eigenspaces of AA such that AViVi1+Vi+Vi+1A^* V_i \subseteq V_{i-1} + V_{i} + V_{i+1} for 0id0 \leq i \leq d, where V1=0V_{-1}=0 and Vd+1=0V_{d+1}=0; (iii) there exists an ordering {Vi}i=0δ\lbrace V^*_i\rbrace_{i=0}^\delta of the eigenspaces of AA^* such that AViVi1+Vi+Vi+1A V^*_i \subseteq V^*_{i-1} + V^*_{i} + V^*_{i+1} for 0iδ0 \leq i \leq \delta, where V1=0V^*_{-1}=0 and Vδ+1=0V^*_{\delta+1}=0; (iv) there is no subspace WW of VV such that AWWAW \subseteq W, AWWA^* W \subseteq W, W0W \neq 0, WVW \neq V. We call such a pair a {\it tridiagonal pair} on VV. It is known that d=δd=\delta and for 0id 0 \leq i \leq d the dimensions of Vi,Vdi,Vi,VdiV_i,V_{d-i},V^*_i, V^*_{d-i} coincide. The pair A,AA,A^* is called {\it sharp} whenever dimV0=1{\rm dim} V_0=1. It is known that if FF is algebraically closed then A,AA,A^* is sharp. In this paper we classify up to isomorphism the sharp tridiagonal pairs. As a corollary, we classify up to isomorphism the tridiagonal pairs over an algebraically closed field. We obtain these classifications by proving the μ\mu-conjecture.

Keywords

Cite

@article{arxiv.1001.1812,
  title  = {A classification of sharp tridiagonal pairs},
  author = {Tatsuro Ito and Kazumasa Nomura and Paul Terwilliger},
  journal= {arXiv preprint arXiv:1001.1812},
  year   = {2010}
}

Comments

36 pages

R2 v1 2026-06-21T14:33:28.011Z