[Paper Review] False Signals of CP-Invariance Violation at DUNE

André de Gouvêa, Kevin J. Kelly|arXiv (Cornell University)|May 30, 2016

Neutrino Physics Research95 references22 citations

TL;DR

This paper demonstrates that CP-conserving new physics—specifically non-standard neutrino interactions (NSI) and a fourth neutrino—can mimic large CP-invariance violation in DUNE's neutrino oscillation data, leading to false signals of CP violation. The key result is that DUNE alone cannot distinguish these scenarios from genuine three-neutrino CP violation, but combining DUNE data with long-baseline experiments like Hyper-Kamiokande can resolve the ambiguity.

ABSTRACT

One of the main goals of the Deep Underground Neutrino Experiment (DUNE) is to look for new sources of CP-invariance violation. Another is to significantly test the three-massive-neutrinos paradigm. Here, we show that there are CP-invariant new physics scenarios which, as far as DUNE data are concerned, cannot be distinguished from the three-massive-neutrinos paradigm with very large CP-invariance violating effects. We discuss examples with non-standard neutrino interactions and with a fourth neutrino mass eigenstate. We briefly discuss how ambiguities can be resolved by combining DUNE data with data from other long-baseline experiments, including Hyper-Kamiokande.

Motivation & Objective

• To investigate whether CP-conserving new physics scenarios can produce false signals of CP-invariance violation in DUNE's neutrino oscillation data.
• To assess the robustness of DUNE's ability to distinguish between the three-neutrino paradigm with large CP violation and alternative CP-conserving new physics models.
• To evaluate whether long-baseline experiments like Hyper-Kamiokande can resolve the degeneracy between these scenarios.
• To identify experimental signatures that could disentangle new physics from genuine CP violation in future oscillation experiments.

Proposed method

• Simulates DUNE's neutrino appearance and disappearance channels using the three-neutrino framework with CP-violating phases and non-standard interactions (NSI).
• Constructs a four-neutrino model with a sterile neutrino eigenstate and extends the PMNS matrix to include additional mixing parameters.
• Performs a global fit of oscillation probabilities to identify parameter sets in NSI and four-neutrino scenarios that reproduce DUNE's expected data with high fidelity.
• Compares predicted $P_{\mu e}$ transition probabilities at DUNE (1300 km) and Hyper-K (295 km) baselines to identify discrepancies that break degeneracy.
• Analyzes the role of matter effects and vacuum propagation to isolate the origin of the fake CP-violation signal.
• Evaluates the potential of high-statistics, high-precision measurements at different $L/E_{\nu}$ ratios to resolve parameter degeneracies.

Experimental results

Research questions

• RQ1 Can CP-conserving new physics such as NSI or a fourth neutrino mimic large CP-invariance violation in DUNE's data?
• RQ2 To what extent can DUNE alone distinguish between genuine three-neutrino CP violation and CP-conserving new physics?
• RQ3 How do $L/E_{\nu}$-dependent differences in oscillation probabilities at DUNE and Hyper-K help resolve the ambiguity between competing models?
• RQ4 What role do matter effects play in generating false CP-violation signals in NSI and four-neutrino scenarios?
• RQ5 Can future experiments with distinct $L/E_{\nu}$ values break the degeneracy between new physics and standard CP-violating scenarios?

Key findings

• Non-standard neutrino interactions (NSI) with a complex $\epsilon_{ee}$ parameter can produce a $P_{\mu e}$ signal at DUNE that closely mimics large CP violation in the three-neutrino paradigm.
• A four-neutrino scenario with a sterile neutrino eigenstate can also reproduce DUNE's expected $P_{\mu e}$ data with a fake CP-violating signal, even when the underlying physics is CP-conserving.
• The fake CP-violation signal is robust at DUNE's 1300 km baseline, where the three-neutrino and new-physics models agree within 1–2% for the best-fit parameters.
• At Hyper-K's 295 km baseline, the two models disagree by up to 25% in $P_{\mu e}$, providing a clear experimental handle to distinguish them.
• The degeneracy cannot be resolved by DUNE alone, nor by measurements of $\nu_\mu$ disappearance or solar parameters, due to insensitivity to CP-violating effects.
• High-precision, high-statistics measurements at different $L/E_{\nu}$ ratios—especially at Hyper-K—can resolve the ambiguity, as the models diverge significantly at distinct baselines.