Direct neutrino mass determination: Status and prospects

More than 80 years after the prediction of their existence, there are still many open questions regarding the nature and properties of neutrinos. Among these questions is the issue of neutrino mass. While oscillation experiments have proven that neutrinos possess non-zero masses, these measurements cannot determine the absolute mass scale. Information on absolute neutrino masses can be deduced either from cosmological observations of large scale structure formation, from the search for neutrino-less double β-decay or from the study of the kinematics of weak decays. While the first two methods are subject to model dependencies or rather large systematical uncertainties, measurements based on the kinematics of nuclear β-decay or electron-capture reactions offer a model-independent way to determine the neutrino mass. This paper provides an overview of status and sensitivities of direct neutrino mass experiments currently under construction (KATRIN, MARE) or in development (Project 8, ECHO).