@article{maas_2007,  title={On the Faddeev-Popov operator eigenspectrum in topological background fields},  volume={37},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332007000400007},  DOI={10.1590/S0103-97332007000400007},  number={2b},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Maas, Axel},  year={2007},  month={Jul},  pages={514–519} }