Cosmic chronometers constraints on some fast-varying dark energy
  equations of state
  We consider three `four-parameters' dark energy equations of state allowing
fast transition from the matter dominated decelerating phase to the current
accelerating phase. The fast-varying nature of the dark energy models is
quantified by the transition width $\tau > 0$, a free parameter associated with
the models where lower values of $\tau$ imply faster transition. We impose the
latest observational constraints on these fast-varying dark energy equations of
state, using the latest released cosmic chronometers data along with a series
of standard dark energy probes, namely, the local Hubble constant value at 2.4%
precision measured by the Hubble Space Telescope, the Joint Light Curve
Analysis from Supernovae Type Ia, Baryon acoustic oscillations distance
measurements and finally the cosmic microwave background radiation distance
priors. Our analyses show that the precise measurements of the free parameters,
when a large number of parameters are allowed in a cosmological model become
very hard. Moreover, the analyses do not enable us to make any decisive comment
on the fast-varying nature of the models, at least from the astronomical data
available at current moment. Finally, we close the work with a discussion based
on the information criteria, which do not return favorable results to the
fast-varying models, at least according to the data employed.
