Beyond-the-Standard-Model Physics in the Neutrino Sector

TL;DR

This chapter surveys how beyond-the-Standard-Model physics can manifest in the neutrino sector. It organizes signatures into oscillation deviations caused by new light states or interactions and dark-sector production at near-detector facilities, highlighting the role of high-intensity beams and precise detectors. It discusses concrete targets such as sterile neutrinos, non-standard neutrino interactions, scalar NSI, heavy neutral leptons, dark photons, and light dark matter, along with current constraints and near-term prospects from experiments like NOvA, T2K, COHERENT, and DUNE. By integrating neutrino- and beam-based searches, the work demonstrates how upcoming facilities can substantially improve sensitivity to new particles or interactions and potentially reveal novel aspects of fundamental physics.

Abstract

Neutrino oscillations are a phenomenon that has been observed for over two decades and leads to the conclusion that neutrinos have mass. The Standard Model predicts massless neutrinos, and so neutrinos require physics beyond the Standard Model. Other signatures of BSM physics are detectable in modern neutrino facilities -- this chapter explores those possibilities. These can range from new effects modifying neutrino oscillations (beyond the expectations when neutrinos have mass), to searches for new particles in neutrino facilities. Next-generation experiments are particularly powerful for these searches due to high-intensity neutrino beams and novel detection technologies. We give an introduction to these search strategies, giving a non-comprehensive overview of the field as it stands presently.

Figures (2)

• Figure 1: Two characteristic diagrams contributing to neutrino trident scattering, (left) in the Standard Model via $W$-boson exchange, and (right) with the inclusion of a new $Z^\prime$ gauge boson that couples to neutrinos and charged leptons.
• Figure 2: Schematic depicting two classes of beyond-the-SM searches possible in neutrino facilities, specifically those sourced by high-intensity proton beams. The top option demonstrates the production of light dark matter via the decay chain $\pi^0 \to \gamma A^\prime$ (dark photon), $A^\prime \to \chi \bar{\chi}$ (dark matter), where the dark matter $\chi$ scatters in the detector with an electron and provides a very high-energy, forward-going electron as its signature. The bottom option shows the possible production of a heavy neutral lepton $N$ via charged-kaon decay, where the heavy neutral lepton can travel to, and decay inside the detector via a process such as $N \to \nu \mu^+ \mu^-$.