Homotopy field theory in dimension 3 and crossed group-categories

由交叉模分级的幺半范畴与三维HQFT

Monoidal categories graded by crossed modules and 3-dimensional HQFTs

本文引入由交叉模分级的幺半范畴与融合范畴，并利用球面χ-融合范畴通过状态和方法构造以同伦2型Bχ为目标的三维同伦量子场论。

On the Homotopy Type and the Fundamental Crossed Complex of the Skeletal Filtration of a CW-Complex

We prove that if $M$ is a CW-complex, then the homotopy type of the skeletal filtration of $M$ does not depend on the cell decomposition of $M$ up to wedge products with $n$-disks $D^n$, when the later are given their natural CW-decomposition with unique cells of order 0, $(n-1)$ and $n$; a result resembling J.H.C. Whitehead's work on simple homotopy types. From the Colimit Theorem for the Fundamental Crossed Complex of a CW-complex (due to R. Brown and P.J. Higgins), follows an algebraic analogue for the fundamental crossed complex $Π(M)$ of the skeletal filtration of $M$, which thus depends …

On 2-Dimensional Homotopy Invariants of Complements of Knotted Surfaces

We prove that if $M$ is a CW-complex and $*$ is a 0-cell of $M$, then the crossed module $Π_2(M,M^1,*)$ does not depend on the cellular decomposition of $M$ up to free products with $Π_2(D^2,S^1,*)$, where $M^1$ is the 1-skeleton of $M$. From this it follows that if $G$ is a finite crossed module and $M$ is finite, then the number of crossed module morphisms $Π_2(M,M^1,*) \to G$ (which is finite) can be re-scaled to a homotopy invariant $I_G(M)$ (i. e. not dependent on the cellular decomposition of $M$). We describe an algorithm to calculate $π_2(M,M^{(1)},*)$ as a crossed module over $π_1(M^{…

交叉模交叉辫子范畴

Crossed-module crossed braided categories

本文为交叉模引入交叉辫子（及缎带）范畴，统一推广了多种已知结构，并利用上同调分类了分级向量空间上的此类结构，还通过扭曲局部模构造了实例。

On Yetter's Invariant and an Extension of the Dijkgraaf-Witten Invariant to Categorical Groups

We give an interpretation of Yetter's Invariant of manifolds $M$ in terms of the homotopy type of the function space $TOP(M,B(G))$, where $G$ is a crossed module and $B(G)$ is its classifying space. From this formulation, there follows that Yetter's invariant depends only on the homotopy type of $M$, and the weak homotopy type of the crossed module $G$. We use this interpretation to define a twisting of Yetter's Invariant by cohomology classes of crossed modules, defined as cohomology classes of their classifying spaces, in the form of a state sum invariant. In particular, we obtain an extensi…

The Fundamental Crossed Module of the Complement of a Knotted Surface

We prove that if $M$ is a CW-complex and $M^1$ is its 1-skeleton then the crossed module $Π_2(M,M^1)$ depends only on the homotopy type of $M$ as a space, up to free products, in the category of crossed modules, with $Π_2(D^2,S^1)$. From this it follows that, if $G$ is a finite crossed module and $M$ is finite, then the number of crossed module morphisms $Π_2(M,M^1) \to G$ can be re-scaled to a homotopy invariant $I_G(M)$, depending only on the homotopy 2-type of $M$. We describe an algorithm for calculating $π_2(M,M^{(1)})$ as a crossed module over $π_1(M^{(1)})$, in the case when $M$ is the …