Radiative Correction from Secret Neutrino Interactions and Implications for Neutrino-Scattering Experiments

TL;DR

The paper investigates how light neutrinophilic mediators can induce radiative corrections to neutrino electroweak couplings, providing a UV-complete SU(2)_L triplet extension that yields finite one-loop corrections to $Z$ and $W$ couplings. It derives explicit expressions for the corrections, revealing a momentum-dependent $g_Z$ but a largely constant $g_W$, and discusses the resulting running behavior of the weak mixing angle across neutrino DIS and CE$\nu$NS processes. By combining precision constraints from the invisible $Z$ width, NSI measurements, and solar-neutrino experiments such as Borexino, the work maps out viable regions in the mediator mass $m_φ$ and coupling $|λ|$, highlighting that NSI constraints can dominate for $m_φ \lesssim \mathcal{O}({\rm GeV})$ and that a joint analysis of multiple probes is essential to break degeneracies with SM running. The study thus demonstrates how a global program of neutrino scattering and solar-neutrino experiments can robustly test νSI scenarios and motivates future high-precision measurements, including $\nu$DIS, CE$\nu$NS, and $e\nu$ scattering, to fully explore the parameter space of neutrinophilic mediators.

Abstract

New, neutrinophilic mediators are one potential extension beyond the Standard Model of particle physics. Often, studies of neutrinophilic mediator consist of searching for direct evidence of its production and/or its tree-level virtual effect for generating strong neutrino self-interaction. In this work, we focus instead on the fact that such new mediators \textit{also} lead to deviations in neutrino-matter scattering via radiative corrections. With a mediator mass well below the electroweak scale, these effects are potentially observable in a variety of contexts, including coherent elastic neutrino-nucleus scattering (CEvNS), neutrino deeply-inelastic scattering ($ν$DIS), and neutrino-electron scattering (e.g., at Borexino). Additionally, such effects lead to new contributions to the $Z$-boson decay width and to non-standard neutrino interactions relevant for long-baseline oscillation experiments. We explore all of these scenarios in some depth, building on the rich phenomenology associated with neutrinophilic mediators.

Figures (8)

• Figure 1: Radiative correction to the $Z\nu\bar{\nu}$ coupling as a function of momentum transfer $Q$ in the presence of a light scalar $\phi$ that mediates neutrino self-interaction. $M=1\,$TeV, $\lambda_{\alpha\gamma}\lambda_{\beta\gamma}^*=1$.
• Figure 2: If one absorbs the novel $Q$-dependence of $g_Z$ into the running of the weak mixing angle, the corresponding values of $\sin^2\theta_W$ needed for interpret the neutrino DIS and CE$\nu$NS experiments are shown by the left and right panels, respectively, taking $M=1\,$TeV, $\lambda_{\mu\mu}=0.5$. The left-panel includes the measurement using $\nu$DIS from NuTeV NuTeV:2001whx; the right includes measurements determined from the COHERENT DeRomeri:2022twg and Dresden-II AristizabalSierra:2022axl experiments' results.
• Figure 3: Sensitivity to $\nu_\tau$ self-interactions from existing experimental bounds for two values of the scalar triplet mediator mass (left and right panels). Shaded regions show limits derived from a global analysis of non-standard neutrino interactions using oscillation and scattering data Coloma:2023ixt and from atmospheric neutrino data in Super-Kamiokande Super-Kamiokande:2011dam, both at $90\%$ CL. Current bounds at the $2\sigma$ C.L. from other sources are shown in gray, including IceCube measurements of ultra-high-energy astrophysical neutrinos Esteban:2021tub, the invisible $Z$ decay width (revisited in this work), and cosmologically relevant regions corresponding to the moderately interacting neutrinos (MI$\nu$) solution, indicated by the light green band.
• Figure 4: Differential cross sections for neutrino–electron elastic scattering, including electroweak radiative corrections (solid) and in the presence of $\nu$SI (dashed), shown for each neutrino flavor. The effect of $\nu$SI reduces the cross section for muon and tau neutrinos and induces a slight tilt in the electron-neutrino spectrum due to the charged-current contribution.
• Figure 5: Event spectrum of elastic electron–neutrino scattering as a function of the number of hits. Borexino Phase-III (subtracted) data are compared with the total predicted signal (black) and with the prediction including $\nu$SI (pink). Solid lines show the individual solar-neutrino components for the best-fit flux normalizations (Standard Model only), while dashed lines show a $\nu$SI scenario with $m_\phi = 10~\rm MeV$ and $\lambda = 1.5$. The total background is indicated by the gray line. In the lower panel, the relative deviation of the prediction including $\nu$SI from the total predicted signal is shown, with the total predicted signal normalized to 1.