[Paper Review] XENON1T constraints on neutrino non-standard interactions

Siddhartha Karmakar, Sujata Pandey|arXiv (Cornell University)|Jul 23, 2020

Dark Matter and Cosmic Phenomena4 citations

TL;DR

This paper uses XENON1T's low-energy electron recoil data to constrain neutrino non-standard interactions (NSI) mediated by a kinetically mixed light $Z^{ackprime}$ boson. It shows that XENON1T provides the most stringent bounds on $Z^{ackprime}$-neutrino couplings for $m_{Z^{ackprime}} \lesssim 300$ keV, surpassing traditional astrophysical bounds like red giant cooling in key regions, and identifies a viable scenario (case 2a) that could explain the XENON1T 2 keV excess while remaining consistent with constraints.

ABSTRACT

The new XENON1T observation of dark matter-electron scattering cross-section, along with further constraining many popular dark matter models, has indicated the possibility of new physics at a low energy. We point out that this new observation also significantly constrain the neutrino non-standard interactions (NSI). We consider the NSI arising from a kinetically mixed $Z'$ with renormalisable and dipole-like interactions with the active and light sterile neutrinos. In passing, we also address the possibility of explaining the XENON1T excess around electron recoil energy ~ 2 keV in presence of such NSI.

Motivation & Objective

• To constrain neutrino non-standard interactions (NSI) mediated by a light $Z^\prime$ boson using XENON1T's low-energy electron recoil data.
• To evaluate the viability of $Z^\prime$-mediated NSI in explaining the XENON1T excess at ~2 keV electron recoil energy.
• To compare XENON1T constraints with existing bounds from red giant cooling, supernova cooling, and Borexino, particularly in scenarios involving active and sterile neutrinos.
• To assess the impact of sterile neutrino masses and $Z^\prime$-neutrino coupling types (renormalizable, dipole) on the resulting constraints.
• To determine whether any NSI scenario can simultaneously explain the XENON1T excess and satisfy stringent astrophysical and cosmological bounds.

Proposed method

• Modeling NSI via a kinetically mixed $Z^\prime$ boson that couples to active and light sterile neutrinos through renormalizable and dipole-type interactions.
• Computing the differential cross-section for neutrino-electron scattering using the amplitude derived from the $Z^\prime$-neutrino interaction Lagrangian, including kinematic factors and $\epsilon$-dependent mixing.
• Applying the XENON1T efficiency factor $\epsilon_{\text{eff}}(E_R)$ and integrating over the solar neutrino flux (pp, $^7$Be, $^8$Be, hep) to compute the event rate.
• Using $\chi^2$-fitting to determine the best-fit constraints on the coupling $g\epsilon$ for various $m_{Z^\prime}$ and $m_N$ values.
• Comparing constraints from XENON1T with those from red giant cooling (RG), supernova (SN) cooling, and Big Bang Nucleosynthesis (BBN), particularly for sterile neutrino scenarios.
• Evaluating the role of $Ne \to Ne$ elastic scattering via $Z^\prime$ exchange, which dominates over inelastic $\nu e \to Ne$ at high $m_N$ and $E_\nu \sim m_N$.

Experimental results

Research questions

• RQ1 How do XENON1T's low-energy electron recoil data constrain $Z^\prime$-mediated neutrino non-standard interactions (NSI) with active and sterile neutrinos?
• RQ2 Can any $Z^\prime$-mediated NSI scenario explain the XENON1T excess at ~2 keV electron recoil energy while remaining consistent with astrophysical bounds?
• RQ3 What is the relative strength of XENON1T constraints compared to red giant cooling and supernova cooling bounds across different $m_{Z^\prime}$ and $m_N$ regions?
• RQ4 How does the dominance of $Ne \to Ne$ scattering over $\nu e \to Ne$ affect the constraints for heavy sterile neutrinos ($m_N \gtrsim 400$ keV)?
• RQ5 In what parameter space does the $Z^\prime$-neutrino coupling remain viable after including constraints from stellar cooling and cosmology?

Key findings

• For $m_{Z^\prime} \lesssim 80$ keV, red giant cooling provides the strongest constraint on $Z^\prime$-neutrino couplings via renormalizable interactions (case 1a), but XENON1T surpasses it for $m_{Z^\prime} \gtrsim 80$ keV.
• For dipole interactions with active neutrinos (case 1b), XENON1T provides the most stringent constraints in the range $30~\text{keV} \lesssim m_{Z^\prime} \lesssim 300$ keV, with $g\epsilon \lesssim 2.4 \times 10^{-13}$ at 2σ.
• For $m_{Z^\prime} \lesssim 30$ keV and $m_{Z^\prime} \gtrsim 300$ keV, red giant and supernova cooling bounds dominate over XENON1T, respectively.
• For sterile neutrino scenarios with $m_N \lesssim 10$ keV, red giant cooling is strongest; for $m_N \gtrsim 10$ keV, XENON1T constraints dominate, especially for $m_{Z^\prime} \sim 1$ keV.
• For $m_{Z^\prime} = 150$ keV, XENON1T constraints are stronger than red giant cooling for all $m_N$, indicating its dominance in the keV-scale $Z^\prime$ regime.
• In cases involving dipole interactions with sterile neutrinos (cases 2b and 3b), supernova cooling provides the tightest bounds for $m_N \gtrsim 350$ keV, while XENON1T constraints weaken for $m_N \gtrsim 200$ keV due to the falling solar neutrino flux above 400 keV.