On Isometry Anomalies in Minimal N=(0,1) and N=(0,2) Sigma Models

TL;DR

This paper investigates anomalies in minimal supersymmetric sigma models with homogeneous target spaces, linking global anomalies to local isometry anomalies and demonstrating conditions under which these models are anomaly-free.

Contribution

It establishes a correspondence between global anomalies and local isometry anomalies in supersymmetric sigma models and clarifies anomaly conditions for models with specific target spaces.

Findings

Global anomalies in CP(N-1) relate to Pontryagin classes.

O(N) sigma models are free of global anomalies.

Minimal N=(0,1) models with S^{N-1} target spaces are anomaly-free.

Abstract

The two-dimensional minimal supersymmetric sigma models with homogeneous target spaces $G/H$ and chiral fermions of the same chirality are revisited. We demonstrate that the Moore-Nelson consistency condition revealing a global anomaly in CP(N-1) (with N>2 and ${\mathcal N}=(0,2)$ supersymmetry) due to a nontrivial first Pontryagin class is in one-to-one correspondence with the local anomalies of isometries in these models. These latter anomalies are generated by fermion loop diagrams which we explicitly calculate. In the case of O}(N) sigma models the first Pontryagin class vanishes, so there is no global obstruction for the minimal ${\mathcal N}=(0,1)$ supersymmetrization of these models. We show that at the local level isometries in these models are anomaly free. Thus, there are no obstructions to quantizing the minimal ${\mathcal N}=(0,1)$ models with the $S^{N-1}= SO(N)/SO(N-1)$ target space. This also includes CP(1) (equivalent to $S^{2}$) which is an exceptional case from the CP(N-1) series. We also discuss a relation between the geometric and gauged formulations of the CP}(N-1) models.