Descent equations of Yang--Mills anomalies in noncommutative geometry

Abstract

Consistent Yang--Mills anomalies $\int\om_{2n-k}^{k-1}$ ($n\in\N$, $ k=1,2, \ldots ,2n$) as described collectively by Zumino's descent equations $δ\om_{2n-k}^{k-1}+\dd\om_{2n-k-1}^{k}=0$ starting with the Chern character $Ch_{2n}=\dd\om_{2n-1}^{0}$ of a principal $\SU(N)$ bundle over a $2n$ dimensional manifold are considered (i.e.\ $\int\om_{2n-k}^{k-1}$ are the Chern--Simons terms ($k=1$), axial anomalies ($k=2$), Schwinger terms ($k=3$) etc.\ in $(2n-k)$ dimensions). A generalization in the spirit of Connes' noncommutative geometry using a minimum of data is found. For an arbitrary graded differential algebra $\CC=\bigoplus_{k=0}^\infty \CC^{(k)}$ with exterior differentiation $\dd$, form valued functions $Ch_{2n}: \CC^{(1)}\to \CC^{(2n)}$ and $\om_{2n-k}^{k-1}: \underbrace{\CC^{(0)}\times\cdots \times \CC^{(0)}}_{\mbox{\small $(k-1)$ times}} \times \CC^{(1)}\to \CC^{(2n-k)}$ are constructed which are connected by generalized descent equations $δ\om_{2n-k}^{k-1}+\dd\om_{2n-k-1}^{k}=(\cdots)$. Here $Ch_{2n}= (F_A)^n$ where $F_A=\dd(A)+A^2$ for $A\in\CC^{(1)}$, and $(\cdots)$ is not zero but a sum of graded commutators which vanish under integrations (traces). The problem of constructing Yang--Mills anomalies on a given graded differential algebra is thereby reduced to finding an interesting integration $\int$ on it. Examples for graded differential algebras with such integrations are given and thereby noncommutative generalizations of Yang--Mills anomalies are found.