The Yang--Lee edge singularity is related to the anomalous behaviour of zeroes of the partition function in the two-dimensional Ising model. It was shown by Cardy, that this behaviour is described by the M(2,5) nonunitary minimal model of conformal field theory, known as the Yang--Lee model. This model can be realised as the Ising model above the critical temperature in an imaginary external magnetic field, as the point where the PT symmetry becomes spontaneously broken. In this talk, I will consider the analogue of this scenario in the tricritical Ising model[1], where a three-parameter family of nonunitary PT-symmetric flows exists. I will present our findings regarding massless flows ending in the Yang--Lee model and in a nonunitary "tricritical" point identified as M(2,7). Finally, I will discuss our conjecture on higher nonunitary multicritical points, connected by PT-symmetric nonunitary flows.

 

[1]: M Lencsés, A Miscioscia, G Mussardo, G Takács: Multicriticality in Yang-Lee edge singularity, arXiv:2211.01123