diff -r b5c1a6aec50d -r 08bbcf3ec4d2 text/fields.tex --- a/text/fields.tex Wed Oct 28 21:41:53 2009 +0000 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,42 +0,0 @@ -\nn{This file is obsolete.} - -\todo{beginning of scott's attempt to write down what fields are...} - -\newcommand{\manifolds}[1]{\cM_{#1}} -\newcommand{\closedManifolds}[1]{\cM_{#1}^{\text{closed}}} -\newcommand{\boundaryConditions}[1]{\cM_{#1}^{\bdy}} -Let $\manifolds{k}$ be the groupoid of manifolds (possibly with boundary) of dimension $k$ and diffeomorphisms between them. Write -$\closedManifolds{k}$ for the subgroupoid of closed manifolds. Taking the boundary gives a functor $\bdy : \manifolds{k} \to \closedManifolds{k-1}$. -Both $\manifolds{k}$ and $\closedManifolds{k}$ are symmetric tensor categories under the operation of disjoint union. -\begin{defn} -A \emph{system of fields} is a collection of functors $\cF_k$ associating a `set of fields' to each manifold of dimension at most $n$. - -First, there are functors $\cF_k : \closedManifolds{k} \to \Set$ for each $0 \leq k < n$. We ask that these are tensor functors, so they -take disjoint unions of manifolds to cartesian products of sets. In particular, this means that $\cF_k(\eset)$ is a point; there's only one field -on the empty manifold of any dimension. - -Define the groupoid $\boundaryConditions{k}$ of `manifolds with boundary conditions' as -\begin{equation*} -\setc{(Y; c)}{\begin{array}{c} \text{$Y$ a $k$-manifold} \\ c \in \cC_{k-1}(\bdy Y) \end{array}} -\xymatrix{ \ar@(ru,rd)@<-1ex>[]} -\set{Y \diffeoto Y'} -\end{equation*} -where we think of $f: Y \diffeoto Y'$ as a morphism $(Y; c) \isoto (Y'; \cC_{k-1}(\restrict{f}{\bdy Y})(c))$. -% -%The objects are pairs $(Y; c)$ with $Y$ a manifold (possibly with boundary) of dimension $k$ and $c \in \cC_{k-1}(\bdy Y)$ -%a field on the boundary of $Y$. A morphism $(Y; c) \to (Y'; c')$ is any diffeomorphism $f: Y \to Y'$ such that $\cC_{k-1}(\restrict{f}{\bdy Y})(c) = c'$. -Notice that $\closedManifolds{k}$ is naturally a subgroupoid of $\boundaryConditions{k}$, since a closed manifold has a unique field on its (empty) boundary. - -We now ask that the functors $\cF_k$ above extend to functors $\cF_k : \boundaryConditions{k} \to \Set$ for each $0 \leq k < n$, -and that there is an extra functor at the top level, $\cF_n : \boundaryConditions{n} \to \Vect$. (Notice that for $n$-manifolds we ask for a vector space, not just a set. This isn't essential for the definition, but we will only be interested in this case hereafter.) -We still require that these are tensor functors, and so take disjoint unions of manifolds to cartesian products of sets, or tensor products of vector spaces, as appropriate. - -\scott{Not sure how to say product fields in this setup.} -Finally, notice there are functors $- \times I : \manifolds{k} \to \manifolds{k+1}$ -Finally (?) we ask for natural transformations $- \times I : \cC_k \to \cC_{k+1} \compose (- \times I)$. Thus for each pair $(Y^k; c)$ we have a map $\cC_k($ -\end{defn} -\begin{rem} -Where the dimension of the manifold is clear, we'll often leave off the subscript on $\cC_k$. -\end{rem} - -\todo{end} \ No newline at end of file