Model-independent tests of the time reversal symmetry in neutrino oscillations

• Applicant: Professor Dr. Thomas Schwetz-Mangold
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510963981

Time reversal (T) is a fundamental symmetry of Nature. It refers to the question, of whether the laws governing elementary particles are the same if processes are considered forward or backwards in time. This symmetry is fundamentally related to the symmetry between matter and anti-matter -- the so-called charge-parity (CP) symmetry, which plays a crucial role for the genesis of matter shortly after the Big Bang. An exciting possibility to search for possible violations of these symmetries is offered by neutrino oscillations, a quantum mechanical interference effect which has been well established by a multitude of experiments. The search for CP violation is one of the central goals of current and upcoming oscillation experiments.In this project we want to study a new method to test the T symmetry. It is based on a model-independent observable sensitive to T violation by comparing the neutrino oscillation probabilities at different distances. Conventional searches for CP violation are indirect and depend on model-dependent parameterisations. The approach proposed in this project allows for the first time to search for T violation in neutrinos, as previously no feasible way has been known, and offers therefore a qualitatively new method to interpret neutrino oscillation data in a model-independent way.In this project we will perform realistic simulations of planned experiments to predict the sensitivity to T violation in this general framework. We will identify the key experimental parameters to enhance the sensitivity. While the method is largely model-independent and robust with respect to the possible presence of unknown new physics in the neutrino section, we will study rigorously the underlying physics assumptions. We plan to develop extensions of the T violation test by adopting few physically justified assumptions, which cover a broad range of new physics scenarios. Examples for the latter are sterile neutrinos and non-unitarity effects or exotic neutrino interactions beyond the known ones. In this way we aim for more broad applications of the test, and identify new combinations of neutrino experiments with which such tests can be performed. In summary, the main goal of the project is to establish realistic ways to use neutrino experiments to study the time reversal symmetry.

• DFG Programme: Research Grants