Is there evidence for dark energy evolution?
  Recently, Sahni, Shafielo o & Starobinsky (2014) combined two independent
measurements of $H(z)$ from BAO data with the value of the Hubble constant $H_0
= H(z=0)$, in order to test the cosmological constant hypothesis by means of an
improved version of the $Om$ diagnostic. Their result indicated a considerable
tension between observations and predictions of the $\Lambda$CDM model.
However, such strong conclusion was based only on three measurements of $H(z)$.
This motivated us to repeat similar work on a larger sample. By using a
comprehensive data set of 29 $H(z)$, we find that discrepancy indeed exists.
Even though the value of $\Omega_{m,0} h^2$ inferred from $Omh^2$ diagnostic
depends on the way one chooses to make a summary statistics (weighted mean or
the median), the persisting discrepancy supports the claims of Sahni, Shafielo
o & Starobinsky (2014) that $\Lambda$CDM model may not be the best description
of our Universe.
