# Rest frame vacuum of the Dirac field on spatially flat FLRW spacetimes

## TL;DR

This paper introduces a new rest frame vacuum for the Dirac field on spatially flat FLRW spacetimes, distinguishing it from the adiabatic vacuum and providing a novel way to separate positive and negative frequencies.

## Contribution

The paper proposes a new type of vacuum state for the Dirac field in FLRW spacetimes that differs from the adiabatic vacuum, especially away from Minkowski space.

## Key findings

- Rest frame vacuum separates positive and negative frequencies.
- Differs from adiabatic vacuum except in Minkowski space.
- Provides a new framework for quantum field theory in curved spacetime.

## Abstract

In quantum theory of the free Dirac field on spatially flat FLRW spacetimes we introduce a new type of vacuum able to separate the positive and negative frequencies in the rest frames. This is refereed as the rest frame vacuum shoving that this differs from the adiabatic vacuum apart from the Minkowski spacetime where these two vacua coincide.