Alternative Framework to Quantize Fermionic Fields

A variational framework is developed here to quantize fermionic fields based on the extended stationary action principle. From the first principle, we successfully derive the well-known Floreanini-Jackiw representation of the Schr\"odinger equation for the wave functional of fermionic fields - an equation typically introduced as a postulate in standard canonical quantization. The derivation is accomplished through three key contributions. At the conceptual level, the classical stationary action principle is extended to include a correction term based on the relative entropy arising from field fluctuations. Then, an extended canonical transformation for fermionic fields is formulated that allows us to obtain the quantum version of the Hamilton-Jacobi equation in a form consistent with the Floreanini-Jackiw representation; Third, necessary functional calculus with Grassmann-valued field variables is developed for the variation procedure. The quantized Hamiltonian is verified to generate the Poincar\'e algebra, thus satisfying the symmetry requirements of special relativity. We also show that the framework can be applied to develop theories of interaction between fermionic fields and other external fields such as electromagnetic fields, non-Abelian gauge fields, or another fermionic field. These results further establish that the present variational framework is a novel alternative to derive quantum field theories.