Oscillations in the dark energy EoS: new MCMC lessons
  We study the possibility of detecting oscillating patterns in the equation of
state (EoS) of the dark energy using different cosmological datasets. We follow
a phenomenological approach and study three different oscillating models for
the EoS, one of them periodic and the other two damped (proposed here for the
first time). All the models are characterised by the amplitude value, the
centre and the frequency of oscillations. In contrast to previous works in the
literature, we do not fix the value of the frequency to a fiducial value
related to the time extension of chosen datasets, but consider a discrete set
of values, so to avoid arbitrariness and try and detect any possible time
period in the EoS. We test the models using a recent collection of SNeIa,
direct Hubble data and Gamma Ray Bursts data. Main results are: I. even if
constraints on the amplitude are not too strong, we detect a trend of it versus
the frequency, i.e. decreasing (and even negatives) amplitudes for higher
frequencies; II. the centre of oscillation (which corresponds to the present
value of the EoS parameter) is very well constrained, phantom behaviour is
excluded at $1\sigma$ level and trend which is in agreement with the one for
the amplitude appears; III. the frequency is hard to constrain, showing similar
statistical validity for all the values of the discrete set chosen, but the
best fit of all the scenarios considered is associated with a period which is
in the redshift range depicted by our cosmological data. The "best" oscillating
models are compared with $\Lambda$CDM using dimensionally consistent a Bayesian
approach based information criterion and the conclusion reached is the non
existence of significant evidence against dark energy oscillations.
