We show that the longitudinal beam polarization option at a future electron-positron collider provides an unambiguous distinction between low-scale type-I seesaw models of neutrino mass. In particular, the pair production cross section of the heavy neutrinos in seesaw models is shown to be enhanced for a suitable choice of the initial beam polarization, and the choice is governed by the size of the light-heavy neutrino mixing parameter. Using this effect, one can also probe a previously uncharted parameter space of the left-right seesaw model, which is complementary to the existing searches at both energy and intensity frontiers.

• Received 14 February 2017

DOI:https://doi.org/10.1103/PhysRevD.95.115031