Neutrino Helicity Reversal and Fundamental Symmetries

TL;DR

This paper explores the theoretical implications of neutrino helicity reversal in a thought experiment, suggesting the existence of right-handed neutrinos and mechanisms for sterilization and de-sterilization.

Contribution

It introduces a novel gedanken experiment analyzing neutrino helicity reversal and discusses its implications for neutrino properties and symmetries.

Findings

Helicity reversal can lead to the appearance of right-handed neutrinos.

Overtaking right-handed neutrinos can cause de-sterilization.

The formalism contrasts with a modified Dirac neutrino model with a pseudoscalar mass term.

Abstract

A rather elusive helicity reversal occurs in a gedanken experiment in which a massive left-handed Dirac neutrino, traveling at a velocity u < c, is overtaken on a highway by a speeding vehicle (traveling at velocity v with u < v < c). Namely, after passing the neutrino, looking back, one would see a right-handed neutrino (which has never been observed in nature). The Lorentz-invariant mass of the right-handed neutrino is still the same as before the passing. The gedanken experiment thus implies the existence of right-handed, light neutrinos, which are not completely sterile. Furthermore, overtaking a bunch of massive right-handed Dirac neutrinos leads to gradual de-sterilization. We discuss the helicity reversal and the concomitant sterilization and de-sterilization mechanisms by way of an illustrative example calculation, with a special emphasis on massive Dirac and Majorana neutrinos. We contrast the formalism with a modified Dirac neutrino described by a Dirac equation with a pseudoscalar mass term proportional to the fifth current.