diff -r dd9487823529 -r 195a0a91e062 blob1.tex --- a/blob1.tex Mon Oct 27 14:32:00 2008 +0000 +++ b/blob1.tex Tue Oct 28 01:19:24 2008 +0000 @@ -1414,6 +1414,9 @@ \nn{need to define/recall def of (self) tensor product over an $A_\infty$ category} + + + \section{Commutative algebras as $n$-categories} \nn{this should probably not be a section by itself. i'm just trying to write down the outline @@ -1434,7 +1437,7 @@ Let $C_*(X, k)$ denote the singular chain complex of the space $X$ with coefficients in $k$. -\begin{prop} +\begin{prop} \label{sympowerprop} $\bc_*(M^n, k[t])$ is homotopy equivalent to $C_*(\Sigma^\infty(M), k)$. \end{prop} @@ -1533,7 +1536,38 @@ By xxxx and \ref{ktcdprop}, the cyclic homology of $k[t]$ is the $S^1$-equivariant homology of $\Sigma^\infty(S^1)$. Up to homotopy, $S^1$ acts by $j$-fold rotation on $\Sigma^j(S^1) \simeq S^1/j$. -If $k = \z$, we then have +If $k = \z$, $\Sigma^j(S^1)$ contributes the homology of an infinite lens space: $\z$ in degree +0, $\z/j \z$ in odd degrees, and 0 in positive even degrees. +The point $\Sigma^0(S^1)$ contributes the homology of $BS^1$ which is $\z$ in even +degrees and 0 in odd degrees. +This agrees with the calculation in \nn{Loday, 3.1.7}. + +\medskip + +Next we consider the case $C = k[t_1, \ldots, t_m]$, commutative polynomials in $m$ variables. +Let $\Sigma_m^\infty(M)$ be the $m$-colored infinite symmetric power of $M$, that is, configurations +of points on $M$ which can have any of $m$ distinct colors but are otherwise indistinguishable. +The components of $\Sigma_m^\infty(M)$ are indexed by $m$-tuples of natural numbers +corresponding to the number of points of each color of a configuration. +A proof similar to that of \ref{sympowerprop} shows that + +\begin{prop} +$\bc_*(M^n, k[t_1, \ldots, t_m])$ is homotopy equivalent to $C_*(\Sigma_m^\infty(M), k)$. +\end{prop} + +According to \nn{Loday, 3.2.2}, +\[ + HH_n(k[t_1, \ldots, t_m]) \cong \Lambda^n(k^m) \otimes k[t_1, \ldots, t_m] . +\] +Let us check that this is also the singular homology of $\Sigma_m^\infty(S^1)$. +We will content ourselves with the case $k = \z$. +One can define a flow on $\Sigma_m^\infty(S^1)$ where points of the same color repel each other and points of different colors do not interact. +This shows that a component $X$ of $\Sigma_m^\infty(S^1)$ is homotopy equivalent +to the torus $(S^1)^l$, where $l$ is the number of non-zero entries in the $m$-tuple +corresponding to $X$. +The homology calculation we desire follows easily from this. + +\nn{say something about cyclic homology in this case? probably not necessary.}