Inserted: 19 feb 2019
Last Updated: 4 jun 2019
Journal: Discrete Contin. Dyn. Syst.
We are concerned with the blow-up analysis of mean field equations. It has been proven in  that solutions blowing-up at the same non-degenerate blow-up set are unique. On the other hand, the authors in  show that solutions with a degenerate blow-up set are in general non-unique. In this paper we first prove that evenly symmetric solutions on a flat torus with a degenerate two-point blow-up set are unique. In the second part of the paper we complete the analysis by proving the existence of such blow-up solutions by using a Lyapunov-Schmidt reduction method. Moreover, we deduce that all evenly symmetric blow-up solutions come from one-point blow-up solutions of the mean field equation on a "half" torus.