QED in external EM fields

Approximate Truncated Schwinger-Dyson methods have predicted that when massless QED is subjected to strong external magnetic fields, chiral symmetry, which is a good symmetry for massless QED without these external fields, is broken. We use Rational Hybrid Monte Carlo (RHMC) simulations to study lattice QED in a strong constant homogeneous external magnetic field. We use the chiral condensate $\langle\bar{\psi}\psi\rangle$ as an order parameter for chiral symmetry breaking. A non-zero value of this condensate in the limit of zero mass electrons in a strong magnetic field indicates that the magnetic field does break chiral symmetry.