Laboratory constraint on the electric charge of the neutron and the neutrino

TL;DR

This paper revisits laboratory constraints on the electric charges of the neutron and neutrino, providing updated bounds that challenge previous cosmological assumptions and exploring their consistency with the Standard Model and its extensions.

Contribution

It offers new laboratory-based constraints on neutron and neutrino charges without assuming neutrino neutrality, and discusses their compatibility with the Standard Model and anomaly cancellation.

Findings

Laboratory constraints on e_p+e_e, e_n, and e_nu are established.

The neutrino charge constraint is weaker than cosmological bounds but stronger than previous laboratory limits.

A minimal extension of the Standard Model can tighten the constraints on e_n and e_nu.

Abstract

We revisit constraints on the electric charge of the neutron and neutrino as well as on e_p+e_e. We consider phenomenological constraints based on laboratory study of the electrical neutrality of subatomic, atomic, and molecular species under assumption of the conservation of the electric charge in the beta decay, that relates e_p+e_e, e_n, and e_nu. Some previously published constraints utilized an additional assumption e_nu=0, which we do not. We dismiss a cosmological constraint at the level of 10^-35 e utilized by PDG in their Review of particle properties as a controversial one which makes the laboratory constraints on e_nu dominant. The phenomenological constraints from the laboratory experiments are obtained as e_p+e_e=(0.2\pm2.6)10^-21 e, e_n=(-0.4\pm1.1)10^-21 e, and e_nu=(0.6\pm3.2)10^{-21} e. The ones on e_p+e_e and e_n are at the same level as the PDG constraints, while our e_nu constraint is several orders of magnitude weaker than the controversial cosmological result dominated in the PDG constraint, but several orders of magnitude stronger than the other individual e_nu constraints considered by PDG. We also consider consistency of the phenomenological constraints and the SM. The SM ignores the neutrino mass term and cannot describe the neutrino oscillations which makes it not a complete theory but a part of it. We demonstrate that the condition of the cancellation of the triangle anomaly within the complete theory does not disagree with the phenomenological constraints since different extensions of the SM may produce different additional contributions to the anomaly. In particular, we consider a minimal extension of the SM, where leptons (nu,e) are treated the same ways as quarks, which sets e_p+e_e=0 and allows for numerical strengthening the constraint on e_n and e_nu, which is e_n=-e_nu=(-0.4\pm1.0)10^-21 e.