Analyses of Tritium decay spectrum at the end-point have shown hints of a negative mass-squared for the neutrino. If so, it implies that the neutrino is a tachyon. How can we be sure of this empirical conclusion?

Prior estimates of a tachyonic spectrum have included only stable modes with 3-momentum > (tachyonic) mass. But a tachyon has unstable modes with 3-momentum < mass. How do they affect the end-point spectrum?

I report on a full study of the tritium decay in the light of a tachyonic neutrino, and show how the transient modes `fill up' the end-point spectrum.