On the stability of the open-string QED neutron and dark matter

TL;DR

This paper investigates the theoretical stability of a hypothetical QED neutron composed of three quarks interacting via QED, proposing it as a potential dark matter candidate due to its stability and long lifetime.

Contribution

It introduces a phenomenological 1+1 dimensional model showing the QED neutron can be stable, unlike the QED proton, and explores its implications as dark matter.

Findings

QED neutron is stable at 44.5 MeV in the model

QED proton is unstable and cannot form a bound state

QED dark neutron may be produced in heavy-ion collisions

Abstract

We study the stability of a hypothetical QED neutron, which consists of a color-singlet system of two $d$ quarks and a $u$ quark interacting with the QED interaction. As a quark cannot be isolated, the intrinsic motion of the three quarks in the lowest-energy state may lie predominantly in 1+1 dimensions, as in a $d$-$u$-$d$ open string. The attractive $d$-$u$ and $u$-$d$ QED interactions may overcome the weaker repulsive $d$-$d$ QED interaction to bind the three quarks together. We examine the QED neutron in a phenomenological three-body problem in 1+1 dimensions with an effective interaction extracted from Schwinger's exact QED solution in 1+1 dimensions. The phenomenological model in a variational calculation yields a stable QED neutron at 44.5 MeV. The analogous QED proton with two $u$ quarks and a $d$ quark has been found to be too repulsive to be stable and does not have a bound or continuum state, onto which the QED neutron can decay via the weak interaction. Consequently, the QED neutron is stable against the weak decay, has a long lifetime, and is in fact a QED dark neutron. It may be produced following the deconfinement-to-confinement phase transition of the quark gluon plasma in high-energy heavy-ion collisions. Because of the long lifetime of the QED dark neutron, self-gravitating assemblies of QED dark neutrons or dark antineutrons may be good candidates for a part of the primordial dark matter produced during the phase transition of the quark gluon plasma in the evolution of the early Universe.