Effective action for Dirac spinors in the presence of general uniform electromagnetic fields

Some new expressions are found, concerning the one-loop effective action of four dimensional massive and massless Dirac fermions in the presence of general uniform electric and magnetic fields, with $\vec E\cdot \vec H\neq 0$ and $\vec E ^2\neq \vec H ^2$. The rate of pair-production is computed and briefly discussed.