A note on the admissibility of complex BTZ metrics

We perform a nontrivial check of Witten's recently proposed admissibility criterion for complex metrics. We consider the 'quasi-Euclidean' metrics obtained from continuing the BTZ class of metrics to imaginary time. Of special interest are the overspinning metrics, which are smooth in this three-dimensional context. Their inclusion as saddle points in the gravitational path integral would lead to puzzling results in conflict with those obtained using other methods. It is therefore encouraging that the admissibility criterion discards them. For completeness, we perform an analysis of smoothness and admissibility for the family of quasi-Euclidean BTZ metrics at all values of the mass and angular momentum.

Automated summary

We verify Witten's admissibility criterion for complex metrics by examining the 'quasi-Euclidean' metrics obtained from continuing the BTZ class of metrics to imaginary time. We focus on the smooth overspinning metrics, which would lead to contradictory results if included as saddle points in the gravitational path integral. The admissibility criterion successfully discards these metrics. Additionally, we analyze the smoothness and admissibility of the quasi-Euclidean BTZ metric family for all values of mass and angular momentum.