  We study the lifetimes of TeV-scale heavy neutral leptons (Majorana
neutrinos) that appear in a model suggested by Okamura et al. [2]. We develop a
convenient way to parametrize the neutrino mass texture of the model, and
illustrate our method by calculating the mass spectrum, decay widths, and
lifetimes of the heavy particles over the entire parameter space. From the mass
spectrum, we find that for most of the parameter space, only two-body decays
are relevant in the calculation of the lifetime, with typical values falling in
the range of 10^(-26) to 10^(-24) seconds. If the particles discussed here are
created at colliders, their lifetimes are short enough for them to decay inside
the detector, while long enough to lead to a narrow peak in the invariant mass
spectrum of the decay products. However, an analysis by Dicus, Karatas, and Roy
[16] suggests that they may be difficult to observe at the LHC.
