Nonunitarity of the lepton mixing matrix at the European Spallation Source

If neutrinos get mass through the exchange of lepton mediators, as in seesaw schemes, the neutrino appearance probabilities in oscillation experiments are modified due to effective nonunitarity of the lepton mixing matrix. This also leads to new CP phases and an ambiguity in underpinning the conventional phase of the three-neutrino paradigm. We study the CP sensitivities of various setups based at the European Spallation Source neutrino super-beam (ESSnuSB) experiment in the presence of nonunitarity. We also examine its potential in constraining the associated new physics parameters. Moreover, we show how the combination of DUNE and ESSnuSB can help further improve the sensitivities on the nonunitarity parameters.

Automated summary

This study explores the modification of neutrino appearance probabilities in oscillation experiments due to the effective nonunitarity of the lepton mixing matrix, which arises if neutrinos obtain mass through the exchange of lepton mediators. Furthermore, the potential of the European Spallation Source neutrino super-beam (ESSnuSB) experiment in constraining the associated new physics parameters is examined, as well as how the combination of DUNE and ESSnuSB can enhance the sensitivities on the nonunitarity parameters.