[Paper Review] Interpretation of the XENON1T excess in the model with decaying sterile neutrinos

V. V. Khruschov|arXiv (Cornell University)|Aug 6, 2020

Neutrino Physics Research16 references4 citations

TL;DR

This paper proposes that the XENON1T electronic recoil excess in the 1–7 keV range arises from decays of two sterile neutrinos with masses 3.4 keV and 7.6 keV, producing dark bosons that subsequently interact with electrons, generating three distinct peaks in the energy spectrum at approximately 1.7 keV, 3 keV, and 3.8 keV. The model assumes a stable 1.1 eV sterile neutrino and small kinetic mixing with photons, offering a unified explanation for the XENON1T anomaly and short-baseline neutrino anomalies.

ABSTRACT

The phenomenological model with three active and three sterile neutrinos is used for interpretation of the observed XENON1T excess of electronic recoil events in the 1 -- 7 keV energy region. Assuming two sterile neutrinos with appropriate mass values decay while the third sterile neutrino is stable it is possible to explain the observed energy spectrum of electronic recoil events. Moreover using this approach three peaks in the 1 -- 7 keV energy region are predicted. Dark bosons have to mix to only a small extent with photons which can be emitted in this region. The possible existence of the three light sterile neutrinos may have perceptible influence on some phenomena in neutrino physics, astrophysics and cosmology.

Motivation & Objective

• To explain the unexplained excess of electronic recoil events in the 1–7 keV energy range observed by the XENON1T experiment.
• To investigate whether the XENON1T excess can be attributed to decays of sterile neutrinos into dark bosons and subsequent electron interactions.
• To test the viability of a (3+1+2) neutrino model—three active and three sterile neutrinos—where two sterile neutrinos decay and one remains stable.
• To explore connections between the XENON1T anomaly, short-baseline neutrino anomalies, and cosmological implications.

Proposed method

• Adopts a (3+1+2) neutrino model with three active and three sterile neutrinos, where two sterile neutrinos (m₅ = 3.4 keV, m₆ = 7.6 keV) decay into dark bosons.
• Assumes the third sterile neutrino (m₄ = 1.1 eV) is stable and dominates the dark matter component.
• Introduces small kinetic mixing between dark bosons and photons to allow for detectable electromagnetic signals in the keV range.
• Models electron recoils via scattering of electrons off dark bosons produced in sterile neutrino decays.
• Uses the Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix to describe neutrino mixing, assuming normal neutrino mass ordering with δCP = 1.2π.
• Predicts three distinct peaks in the electronic recoil energy spectrum at 1.7 keV, 3 keV, and 3.8 keV based on the decay kinematics and dark boson properties.

Experimental results

Research questions

• RQ1 Can the XENON1T electronic recoil excess in the 1–7 keV range be explained by decays of sterile neutrinos into dark bosons?
• RQ2 What specific energy peaks in the electronic recoil spectrum are predicted by the (3+1+2) model with two decaying sterile neutrinos?
• RQ3 How does the inclusion of a stable 1.1 eV sterile neutrino affect cosmological parameters like ΔNeff and the H₀ tension?
• RQ4 Can this model simultaneously explain short-baseline neutrino anomalies such as LSND, reactor, and gallium anomalies?

Key findings

• The model predicts three distinct peaks in the electronic recoil energy spectrum at approximately 1.7 keV, 3 keV, and 3.8 keV, arising from decays of sterile neutrinos with masses 3.4 keV and 7.6 keV.
• The 3.4 keV and 7.6 keV sterile neutrinos decay into dark bosons that subsequently produce electron recoils via weak interactions, explaining the observed excess.
• The stable 1.1 eV sterile neutrino state contributes to the effective number of relativistic species (ΔNeff), potentially influencing cosmological constraints and the H₀ tension.
• Small kinetic mixing between dark bosons and photons allows for detectable electromagnetic signals in the keV range, consistent with XENON1T's sensitivity.
• The model remains viable for explaining short-baseline neutrino anomalies (LSND, reactor, gallium) due to the same sterile neutrino sector.
• Future experiments such as PandaX-4T, LZ, and XENONnT can test the predicted spectral peaks in the 1–7 keV region.