Evolution of chirality in a multiphoton pair production process

Recent years, multiphoton pair production has become one of the most promising approaches to investigate the Schwinger effect. However, the production and evolution of chirality, a key topic in the study of this effect, has not been thoroughly considered in the context of multiphoton pair production. In this work, as the first step of filling this gap, we used the Dirac-Heisenberg-Wigner formalism to study the production and evolution of chirality in vacuum under the excitation of the spatially homogeneous electric and magnetic fields $\mathbf{E}(t)$ and $\mathbf{B}(t)$ that satisfy $\mathbf{E}(t)\parallel\mathbf{B}(t)$ and are only nonzero in a short time span $0<t<\tau$, which serve as a simplified model of the laser beams in multiphoton pair production experiments. Based on analytical calculation, we discovered that, after the external fields vanish, an oscillation of pseudoscalar condensate occurs in the system, which leads to the suppression of the chirality of the produced fermion pairs; at the same time, it introduces a special fermion energy $\epsilon_p=\sqrt{3} m$ at which the chiral charge distribution of the fermions maximizes. This novel phenomenon could help us identify different types of products in future multiphoton pair production experiments.