  In this study we reconsider the phenomenological problems related to
tachyonic modes in the context of extra time-like dimensions. First we
reconsider a lower bound on the size of extra time-like dimensions. Next we
discuss the issues of spontaneous decay of stable fermions through tachyonic
decays and disappearance of fermions due to tachyonic contributions to their
self-energies. We find that the tachyonic modes due to extra time-like
dimensions are less problematic than the tachyonic modes in the usual
4-dimensional setting because the most troublesome Feynman diagrams are
forbidden once the conservation of momentum in the extra time-like dimensions
is imposed.
