Primordial Neutrinos: Hot in SM-GR-$\Lambda$-CDM, Cold in SM-LGT

TL;DR

This paper proposes replacing general relativity with a Lorentz gauge theory of gravity, showing neutrinos can serve as cold dark matter and explaining cosmic acceleration without a cosmological constant.

Contribution

It introduces a Lorentz gauge theory of gravity as an alternative to GR-$\Lambda$-CDM, demonstrating neutrinos as cold dark matter and addressing cosmic acceleration.

Findings

Neutrinos as heavy as 1 eV can be cold dark matter in LGT.

LGT predicts a spin-spin force stronger than gravity affecting fermions.

Vacuum energy does not gravitate in LGT, leading to spontaneous acceleration.

Abstract

We replace general relativity (GR) and the cosmological constant ($\Lambda$) in the standard cosmology (SM-GR-$\Lambda$-CDM) with a Lorentz gauge theory of gravity (LGT) and show that the standard model (SM) neutrinos can be the cold dark matter (CDM) because (i) the expansion of the universe at early times is not as sensitive to the amount of radiation as in the SM-GR-$\Lambda$-CDM and (ii) in LGT there exists a spin-spin long-range force that is very stronger than the Newtonian gravity and interacts with any fermion including neutrinos. Assuming that neutrinos as heavy as 1eV are the cold dark matter, the lower bound on the dimensionless coupling constant of LGT is derived to be $10^{-7}$ which is small enough to be consistent with the upper bound that can be placed by the electroweak precision tests. We also show that the vacuum energy does not gravitate in LGT and a decelerating universe shifts spontaneously to an accelerating one right at the moment that we expect. Therefore, current observations can be explained in our cosmological model (SM-LGT) with lesser assumptions than in the SM-GR-$\Lambda$-CDM.