One parameterisation to fit them all
  Perhaps the most explored hypothesis for the accelerated cosmic expansion
rate arise in the context of extra fields or modifications to General
Relativity. A prevalent approach is to parameterise the expansion history
through the equation of state, $\omega(z)$. We present a parametric form for
$\omega(z)$ that can reproduce the generic behaviour of the most widely used
physical models for accelerated expansion with infrared corrections. The
present proposal has at most 3 free parameters which can be mapped back to
specific archetypal models for dark energy. We analyze in detail how different
combinations of data can constrain the specific cases embedded in our form for
$\omega(z)$. We implement our parametric equation for $\omega(z)$ to
observations from CMB, luminous distance of SNeIa, cosmic chronometers, and
baryon acoustic oscillations identified in galaxies and in the Lymann-$\alpha$
forest. We find that the parameters can be well constrained by using different
observational data sets. Our findings point to an oscillatory behaviour which
is consistent with an $f(R)$-like model or an unknown combination of scalar
fields. When we let the three parameters vary freely, we find an EOS which
oscillates around the phantom-dividing line, and, with over 99$\%$ of
confidence, the cosmological constant solution is disfavored.
