Near the second order phase transition point, QCD with two flavours of massless quarks can be approximated by an O(4) model, where a symmetry breaking external field H can be added to play the role of quark mass.
The Lee-Yang theorem states that the equation of state in this model has a branch cut along the imaginary H axis for |Im[H]|>Hc, where Hc indicates a second order critical point.
This point, known as Lee-Yang edge singularity, is of importance to the thermodynamics of the system.
We report here on ongoing work to determine the location of Hc via complex Langevin simulations.