Interplay of non-standard interactions and Earth's composition in atmospheric neutrino oscillations

TL;DR

This work analyzes how non-standard neutral-current NSI (NC-NSI) could affect atmospheric-neutrino oscillation tomography of the Earth's outer core, particularly its hydrogen content, by combining a PREM-based 55-shell Earth model with Monte Carlo simulations of muon-like events in a large Cherenkov detector. It derives the NC-NSI-modified flavor-evolution Hamiltonian in matter and propagates oscillation probabilities through Earth to predict detector event rates across energy and nadir-angle bins, seeking correlations between outer-core $Z/A$ and NSI parameters. The results reveal degeneracies between core composition and NSI, with sensitivity confined to specific energy-angle windows; longer exposures and better resolutions improve constraints on hydrogen content to a few percent only if NSI coefficients are not too small. The study shows that NSI bounds from this method are compatible with global limits, but density uncertainties and parameter marginalization can dilute the tomographic signal, underscoring the need for joint analyses incorporating both NSI and geophysical uncertainties.

Abstract

Many geophysical and geochemical phenomena in the Earth's interior are related to physical and chemical processes in the outer core and the core-mantle boundary, which are directly linked to the isotopic composition. Determining the composition using standard geophysical methods has been challenging. Atmospheric neutrino oscillations, influenced by their weak interactions with terrestrial matter, offer a new way to gather valuable information about the Earth's internal structure and, in particular, to constrain the composition of the core. If neutrinos had as yet unknown non-standard interactions (NSI), this could affect their propagation in matter and consequently impact studies of Earth's composition using neutrino oscillation tomography. This study focuses on scalar-mediated NSI and their potential impact on atmospheric neutrino oscillations, which could obscure information about the hydrogen content in the outer core. In turn, compositional uncertainties could affect the characterization of NSI parameters. The analysis is based on a Monte-Carlo simulation of the energy distribution and azimuthal angles of neutrino-generated $μ$ events. Using a model of the Earth consisting of 55 concentric shells with constant densities determined from the PREM, we evaluate the effect on the number of events due to changes in the outer core composition (Z/A)$_{oc}$ and the NSI strength parameter $ε$. To examine the detection capability to observe such variations, we consider regions in the plane of (Z/A)$_{oc}$ and $ε$ where the statistical significance of the discrepancies between the modified Earth model and the reference model is less than $1σ$.

Figures (9)

• Figure 1: Neutrino path through the Earth.
• Figure 2: Probability distribution for true and observed events.
• Figure 3: ${R}(\epsilon) = {\mathcal{N}_{\mu}( {\epsilon} )}/{\mathcal{N}_{\mu}( 0 )}$ as a function of a single non-zero entry of the matrix $(\epsilon_{\alpha\beta})$, for the standard Earth and normal and inverted ordering. (a) and (b) Diagonal coefficients $\epsilon_{ee}-\epsilon_{\mu\mu}, \epsilon_{\tau\tau}-\epsilon_{\mu\mu}$. (c) and (d) Modulus of non-diagonal coefficients $\epsilon_{e\mu}, \epsilon_{e\tau}, \epsilon_{\mu\tau}$.
• Figure 4: Bounds on the modulus and phase of the non-diagonal entries of the matrix $(\epsilon_{\alpha\beta})$, for (a) normal ordering and (b) inverted ordering. The allowed values fall in the regions under the curves, where the discrepancy between the events with and without the NSI is less than $1\sigma$.
• Figure 5: Entries of the matrix $(\epsilon_{\alpha\beta})$ as a function of the outer core composition. Entries are considered nonzero, one at a time. (a) and (b) Diagonal coefficients $\epsilon_{ee} - \epsilon_{\mu\mu}$, $\epsilon_{\tau\tau} - \epsilon_{\mu\mu}$. (c) and (d) Non-diagonal coefficients $\epsilon_{e\mu}$, $\epsilon_{e\tau}$, $\epsilon_{\mu\tau}$, with the respective phases marginalized. In the regions enclosed by the contours, the difference between events with non-standard $(Z/A)_{oc}$ and/or NSI and those for the standard Earth without NSI (the black dot in the figures) is less than a significance level of $1\sigma$, for normal and inverted mass ordering. The regions to the right of the vertical dashed line correspond to the standard composition plus the addition of hydrogen in the outer core.