The flavor vacuum in the expanding universe and dark matter

TL;DR

This paper investigates how fermion mixing in curved spacetime leads to a flavor vacuum that behaves like dark matter, suggesting a quantum origin for this cosmological component.

Contribution

It demonstrates that the flavor vacuum of mixed fermions in an expanding universe acts as a perfect fluid consistent with dark matter, linking quantum effects to cosmological phenomena.

Findings

The energy momentum tensor of the flavor vacuum is diagonal and conserved.

The flavor vacuum behaves like cold dark matter in a De Sitter background.

Quantum fermion mixing may contribute to the dark matter component.

Abstract

We analyze fermion mixing in the framework of field quantization in curved spacetime. We compute the expectation value of the energy momentum tensor of mixed fermions on the flavor vacuum. We consider spatially flat Friedmann-Lemaitre-Robertson-Walker metrics, and we show that the energy momentum tensor of the flavor vacuum is diagonal and conserved. Therefore it can be interpreted as the effective energy momentum tensor of a perfect fluid. In particular, assuming a fixed De Sitter background, the equation of state of the fluid is consistent with that of dust and cold dark matter. Our results establish a new link between quantum effects and classical fluids, and indicate that the flavor vacuum of mixed fermions may represent a new component of dark matter.