Partition function zeros of quantum many-body systems

We present a new method for calculating the Yang-Lee partition function zeros of a translationally invariant model of lattice fermions, exemplified by the Hubbard model. The method rests on a theorem involving the single electron self-energy $\Sigma_\sigma(k, i \omega_n)$ in the imaginary time Matsubara formulation. The theorem maps the Yang-Lee zeros to a set of wavevector and spin labeled virtual energies $\xi_{k \sigma}$. These, thermodynamically derived virtual energies, are solutions of equations involving the self-energy at corresponding $k\sigma$'s. Examples of the method in simplified situations are provided.