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子因子模不变量

Modular invariants from subfactors

J. Böckenhauer, D. E. Evans

摘要:

在这些讲座中,我们将解释共形域论中的模不变量与算子代数中的辫子子因子之间的密切关系。具有编织的子因子确定矩阵$Z$,该矩阵作为比较两种编织扇区感应(“α-感应”)的耦合矩阵而获得。它具有非负整数元素,是归一化的,并与由编织产生的S矩阵和T矩阵交换。因此,它是一个在通常意义上的有理共形域论的物理模不变量。共形域论模型的代数处理,例如$SU(n)_k$模型,产生子因子,实现其已知的模不变量。迄今为止,模不变量的几个性质已经被经验地注意到,并被认为是神秘的,例如它们与图的密切关系,例如$SU(2)_k$的A-D-E分类。在子因子上下文中,这些属性可以在非常一般的设置中严格导出。此外,Moore-Seiberg,Dijkgraaf-Verlinde通过中间子因子找到了最大扩展手征代数的融合规则同构,甚至没有涉及$S$和$T$的模块性。最后,我们给出了一个概述的现状之间的关系的分类辫子子和二维共形域论的事态。我们特别演示了如何实现扭曲(II型)后裔模不变量的共形包含子因子,并说明了新的例子的方法。

英文摘要:

In these lectures we explain the intimate relationship between modular invariants in conformal field theory and braided subfactors in operator algebras. A subfactor with a braiding determines a matrix $Z$ which is obtained as a coupling matrix comparing two kinds of braided sector induction ("alpha-induction"). It has non-negative integer entries, is normalized and commutes with the S- and T-matrices arising from the braiding. Thus it is a physical modular invariant in the usual sense of rational conformal field theory. The algebraic treatment of conformal field theory models, e.g. $SU(n)_k$ models, produces subfactors which realize their known modular invariants. Several properties of modular invariants have so far been noticed empirically and considered mysterious such as their intimate relationship to graphs, as for example the A-D-E classification for $SU(2)_k$. In the subfactor context these properties can be rigorously derived in a very general setting. Moreover the fusion rule isomorphism for maximally extended chiral algebras due to Moore-Seiberg, Dijkgraaf-Verlinde finds a clear and very general proof and interpretation through intermediate subfactors, not even referring to modularity of $S$ and $T$. Finally we give an overview on the current state of affairs concerning the relations between the classifications of braided subfactors and two-dimensional conformal field theories. We demonstrate in particular how to realize twisted (type II) descendant modular invariants of conformal inclusions from subfactors and illustrate the method by new examples.

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