# HG changeset patch # User Kevin Walker # Date 1290021960 28800 # Node ID 9c09495197c08053893405258a36ead2f1162ffe # Parent 6a7f2a6295d1ddb2e71a1b723d76f980eb6f302f# Parent 11f8331ea7c4eeac7012eb41b123e419b7f7f685 trying to resolve diff -r 11f8331ea7c4 -r 9c09495197c0 pnas/build.xml --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/pnas/build.xml Wed Nov 17 11:26:00 2010 -0800 @@ -0,0 +1,82 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff -r 11f8331ea7c4 -r 9c09495197c0 pnas/pnas.tex --- a/pnas/pnas.tex Wed Nov 17 11:16:39 2010 -0800 +++ b/pnas/pnas.tex Wed Nov 17 11:26:00 2010 -0800 @@ -96,7 +96,7 @@ %% For titles, only capitalize the first letter %% \title{Almost sharp fronts for the surface quasi-geostrophic equation} -\title{$n$-categories, colimits and the blob complex} +\title{Higher categories, colimits and the blob complex} %% Enter authors via the \author command. @@ -158,47 +158,43 @@ %% \subsection{} %% \subsubsection{} -\dropcap{T}he aim of this paper is to describe a derived category version of TQFTs. +\dropcap{T}he aim of this paper is to describe a derived category analogue of topological quantum field theories. For our purposes, an $n{+}1$-dimensional TQFT is a locally defined system of -invariants of manifolds of dimensions 0 through $n+1$. -The TQFT invariant $A(Y)$ of a closed $k$-manifold $Y$ is a linear $(n{-}k)$-category. +invariants of manifolds of dimensions 0 through $n+1$. In particular, +the TQFT invariant $A(Y)$ of a closed $k$-manifold $Y$ is a linear $(n{-}k)$-category. If $Y$ has boundary then $A(Y)$ is a collection of $(n{-}k)$-categories which afford a representation of the $(n{-}k{+}1)$-category $A(\bd Y)$. (See \cite{1009.5025} and \cite{kw:tqft}; for a more homotopy-theoretic point of view see \cite{0905.0465}.) We now comment on some particular values of $k$ above. -By convention, a linear 0-category is a vector space, and a representation +A linear 0-category is a vector space, and a representation of a vector space is an element of the dual space. -So a TQFT assigns to each closed $n$-manifold $Y$ a vector space $A(Y)$, +Thus a TQFT assigns to each closed $n$-manifold $Y$ a vector space $A(Y)$, and to each $(n{+}1)$-manifold $W$ an element of $A(\bd W)^*$. -In fact we will be mainly be interested in so-called $(n{+}\epsilon)$-dimensional -TQFTs which have nothing to say about $(n{+}1)$-manifolds. -For the remainder of this paper we assume this case. +For the remainder of this paper we will in fact be interested in so-called $(n{+}\epsilon)$-dimensional +TQFTs, which are slightly weaker structures and do not assign anything to general $(n{+}1)$-manifolds, but only to mapping cylinders. When $k=n-1$ we have a linear 1-category $A(S)$ for each $(n{-}1)$-manifold $S$, and a representation of $A(\bd Y)$ for each $n$-manifold $Y$. -The gluing rule for the TQFT in dimension $n$ states that +The TQFT gluing rule in dimension $n$ states that $A(Y_1\cup_S Y_2) \cong A(Y_1) \ot_{A(S)} A(Y_2)$, where $Y_1$ and $Y_2$ and $n$-manifolds with common boundary $S$. When $k=0$ we have an $n$-category $A(pt)$. -This can be thought of as the local part of the TQFT, and the full TQFT can be constructed of $A(pt)$ +This can be thought of as the local part of the TQFT, and the full TQFT can be reconstructed from $A(pt)$ via colimits (see below). We call a TQFT semisimple if $A(S)$ is a semisimple 1-category for all $(n{-}1)$-manifolds $S$ and $A(Y)$ is a finite-dimensional vector space for all $n$-manifolds $Y$. -Examples of semisimple TQFTS include Witten-Reshetikhin-Turaev theories, +Examples of semisimple TQFTs include Witten-Reshetikhin-Turaev theories, Turaev-Viro theories, and Dijkgraaf-Witten theories. These can all be given satisfactory accounts in the framework outlined above. -(The WRT invariants need to be reinterpreted as $3{+}1$-dimensional theories in order to be -extended all the way down to 0-manifolds.) +(The WRT invariants need to be reinterpreted as $3{+}1$-dimensional theories with only a weak dependence on interiors in order to be +extended all the way down to dimension 0.) For other non-semisimple TQFT-like invariants, however, the above framework seems to be inadequate. - -\nn{temp} - For example, the gluing rule for 3-manifolds in Ozsv\'{a}th-Szab\'{o}/Seiberg-Witten theory involves a tensor product over an $A_\infty$ 1-category associated to 2-manifolds \cite{1003.0598,1005.1248}. Long exact sequences are important computational tools in these theories, @@ -539,9 +535,12 @@ \subsubsection{Colimits} -\nn{Motivation: How can we extend an $n$-category from balls to arbitrary manifolds?} +Our definition of an $n$-category is essentially a collection of functors defined on $k$-balls (and homeomorphisms) for $k \leq n$ satisfying certain axioms. It is natural to consider extending such functors to the larger categories of all $k$-manifolds (again, with homeomorphisms). In fact, the axioms stated above explictly require such an extension to $k$-spheres for $k