  In this work we report on the emergence of a novel type of solitary waves,
viz., time-localized solitons in integrable and non-integrable variants of the
massive Thirring models and in the three-wave resonant-interaction system,
which are models broadly used in plasmas, nonlinear optics and hydrodynamics.
An essential finding is that the condition for the existence of time-localized
dark solitons, which develop density dips in the course of time evolution, in
these models coincides with the condition for the occurrence of the
zero-wavenumber-gain (ZWG) modulational instability (MI). Systematic
simulations reveal that, whenever the ZWG MI is present, patterns reminiscent
of such solitons are generically excited from a chaotic background field as
fragments within more complex patterns.
