Abstract
We discuss time reversal ($T$) violation in neutrino oscillations in generic new physics scenarios. A general parametrization is adopted to describe flavor evolution, which captures a wide range of new physics effects, including nonstandard neutrino interactions, nonunitarity, and sterile neutrinos in a model-independent way. In this framework, we discuss general properties of time reversal in the context of long-baseline neutrino experiments. Special attention is given to fundamental versus environmental $T$ violation in the presence of generic new physics. We point out that $T$ violation in the disappearance channel requires new physics, which modifies flavor mixing at neutrino production and detection. We use time-dependent perturbation theory to study the effect of nonconstant matter density along the neutrino path and quantify the effects for the well-studied baselines of the DUNE, T2HK, and T2HKK projects. The material presented here provides the phenomenological background for the model-independent test of $T$ violation proposed by us in [T. Schwetz and A. Segarra, Model-Independent Test of $T$ Violation in Neutrino Oscillations, Phys. Rev. Lett. 128, 091801 (2022).].
Highlights
The search for the charge-parity (CP) symmetry violation is a central goal for current and upcoming longbaseline neutrino oscillation experiments
Fundamental CP violation is closely related to time reversal T violation thanks to the CPT theorem, which states that the product of these two transformations must be a symmetry
We have studied some aspects of the time reversal transformation in a generic nonstandard neutrino oscillation framework
Summary
The search for the charge-parity (CP) symmetry violation is a central goal for current and upcoming longbaseline neutrino oscillation experiments. The usual search for CP violation is highly model dependent It relies on the standard unitary three-flavor paradigm, implying the absence of any new physics in neutrino interactions, mixing, and propagation. THOMAS SCHWETZ and ALEJANDRO SEGARRA (i) We prosed a rather general parametrization of neutrino evolution to describe the flavor system more model independently, and (ii) We presented a potentially realistic way to search for fundamental T violation in long-baseline experiments. The main idea with respect to item (ii) is the following: We consider the oscillation probabilities within the general framework at different baselines but at the same energy The reason for this assumption is that we want to be agnostic about the energy dependence of the new physics.
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