The Big Bang, CPT, and neutrino dark matter

TL;DR

This paper proposes a CPT-symmetric cosmological model where the universe before and after the Big Bang are mirror images, offering a novel explanation for dark matter and making specific predictions about neutrino properties and gravitational waves.

Contribution

It introduces a CPT-invariant universe model that naturally accounts for dark matter using only standard physics and predicts specific neutrino and gravitational wave properties.

Findings

A right-handed neutrino with mass 4.8×10^8 GeV can explain dark matter.

Predicts three Majorana neutrinos with one massless.

No primordial gravitational waves without inflation.

Abstract

We investigate the idea that the universe before the Big Bang is the $CPT$ reflection of the universe after the bang, both classically and quantum mechanically, so that the universe does {\it not} spontaneously violate $CPT$. We show how $CPT$ symmetry selects a preferred vacuum state for quantum fields on a $CPT$-invariant cosmological background spacetime. The universe before the bang and the universe after the bang may be viewed as a universe/anti-universe pair, emerging directly into the hot, radiation-dominated era we observe in our past. This, in turn, leads to a remarkably economical explanation of the cosmological dark matter. With no additional fields beyond Einstein gravity and the standard model of particle physics (including right-handed neutrinos), a $\mathbb{Z}_{2}$ symmetry stabilizes one of the right-handed neutrinos. We calculate its abundance in detail and show that, in order to match the observed dark matter density, its mass must be $4.8\times10^{8}~{\rm GeV}$. We obtain several further predictions, including: (i) that the three light neutrinos are majorana; (ii) that one of these is exactly massless; and (iii) that, in the absence of an epoch of cosmic inflation, there should be no primordial, long-wavelength gravitational waves. We also briefly discuss the natural origin of the matter-antimatter asymmetry within this picture and possibilities for explaining the cosmological perturbations.