  We study the robustness of the quintessence tracking scenario in the context
of more general cosmological models that derive from high-energy physics. We
consider the effects of inclusion of multiple scalar fields, corrections to the
Hubble expansion law (such as those that arise in brane cosmological models),
and potentials that decay with expansion of the Universe. We find that in a
successful tracking quintessence model the average equation of state must
remain nearly constant. Overall, the conditions for successful tracking become
more complex in these more general settings. Tracking can become more fragile
in presence of multiple scalar fields, and more stable when temperature
dependent potentials are present. Interestingly though, most of the cases where
tracking is disrupted are those in which the cosmological model is itself
non-viable due to other constraints. In this sense tracking remains robust in
models that are cosmologically viable.
