Towards Lefschetz Thimbles in Sigma Models, I

We study two dimensional path integral Lefschetz thimbles, i.e. the possible path integration contours. Specifically, in the examples of the O(N) and CPN-1 models, we find a large class of complex critical points of the sigma model actions which are relevant for the theory in finite volume at finite temperature, with various chemical potentials corresponding to the symmetries of the models. In this paper we discuss the case of the O(2m) and the CPN-1 models in the sector of zero instanton charge, as well as some solutions of the O(2m + 1) model. The CPN-1-model for all instanton charges and a more general class of solutions of the O(N)-model with odd N will be discussed in the forthcoming paper.

Automated summary

The study focuses on the complex critical points of the sigma model actions in the O(N) and CPN-1 models, relevant for theories at finite volume and finite temperature. Specifically, the O(2m) and CPN-1 models in the sector of zero instanton charge are discussed, along with some solutions of the O(2m + 1) model. Further discussions on the CPN-1 model for all instanton charges and a more general class of solutions of the O(N) model with odd N will be presented in a forthcoming paper.