Abstract

The discovery of neutrino oscillations invites many fundamental physics questions that have yet to be answered. Two of these questions are simple, easy to state, and essential: What are the values of the neutrino masses? Are neutrinos Majorana fermions? The reason we don't know the answer to those questions is that it is difficult to measure neutrino properties outside of the ultrarelativistic regime. We discuss the physics of $e\gamma\to e\nu\bar{\nu}$ near threshold, where one has access to nonrelativistic neutrinos and only nonrelativistic neutrinos. Near threshold, $e\gamma\to e\nu\bar{\nu}$ is a rich phenomenon and its cross section is sensitive to the individual values of the neutrino masses and the nature of the neutrinos. We show that if one could scan the threshold region, it would be simple to identify the mass of the lightest neutrino, the neutrino mass ordering, and whether the neutrinos are Majorana fermions. In practice, however, event rates are tiny and backgrounds are huge; the observation of $e\gamma\to e\nu\bar{\nu}$ in the sub-eV regime appears to be utterly inaccessible in the laboratory. Our results, nonetheless, effectively illustrate the discriminatory power of nonrelativistic neutrino observables.

Highlights

  • The discovery of neutrino oscillations reveals that neutrinos do not behave as prescribed by the standard model (SM)

  • The discovery of neutrino oscillations reveals that neutrinos have nonzero masses and leptons mix

  • It invites many fundamental physics questions that have the potential to qualitatively change our understanding of particle physics

Read more

Summary

INTRODUCTION

The discovery of neutrino oscillations reveals that neutrinos do not behave as prescribed by the standard model (SM). While the upper bounds derived from these phenomena are nontrivial and point to neutrino masses below the eV scale, a precise determination of the values of the neutrino masses is still lacking It is unknown whether or not the neutrino and its antiparticle are distinct physical objects, i.e., whether neutrinos are Dirac or Majorana fermions. We discuss another process in which neutrino masses can be important: e−γ → e−νν, which we refer to as stimulated ννemission.2 We consider this process when a sub-eV photon impinges on an electron at rest; we probe the threshold region, in which the final state neutrinos can be nonrelativistic.

STIMULATED νν EMISSION
Normal vs inverted mass hierarchies
Dirac vs Majorana fermions
RATES AND BACKGROUNDS
NEW PHYSICS CONTRIBUTIONS
Sterile neutrinos
Neutrino magnetic and electric dipole moments
DISCUSSION AND CONCLUSIONS
Dirac Neutrinos
Majorana neutrinos

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.