Absolute neutrino mass from helicity measurements

The possibility to access the absolute neutrino mass scale through the measurement of the wrong helicity contribution of charged leptons is investigated in pion decay. Through this method, one may have access to the same effective mass $m^2_\beta$ extractable from the tritium beta decay experiments for electron neutrinos as well as the analogous effective mass $(m^2_{\nu_\mu})_{\rm eff}$ for muon neutrinos. In the channel $\pi^-\to e^-\bar{\nu}$, the relative probability of producing an antineutrino with left helicity is enhanced if compared with the naive expectation $(m_\nu/2E_\nu)^2$. The possibility to constrain new interactions in the context of Two-Higgs-Doublet models is also investigated.