# Notes on the Feynman path integral for the Dirac equation

## TL;DR

This paper extends the rigorous construction of the Feynman path integral for the Dirac equation, demonstrating its adherence to unitarity and causality principles in a generalized setting.

## Contribution

It generalizes previous results on the Feynman path integral for the Dirac equation and proves its compliance with unitarity and causality.

## Key findings

- Path integral constructed for all electron paths in space-time
- Proves the path integral satisfies unitarity
- Demonstrates the path integral respects causality

## Abstract

This paper is a continuation of the author's preceding one. In the preceding paper the author has rigorously constructed the Feynman path integral for the Dirac equation in the form of the sum-over-histories, satisfying the superposition principle, over all paths of one electron in space-time that goes in any direction at any speed, forward and backward in time with a finite number of turns. In the present paper, first we will generalize the results in the preceding paper and secondly prove in a direct way that our Feynman path integral satisfies the unitarity principle and the causality one.