Probing the time dependence of dark energy
  A new method to investigate a possible time-dependence of the dark energy
equation of state $w$ is proposed. We apply this methodology to two of the most
recent data sets of type Ia supernova (Union2 and SDSS) and the baryon acoustic
oscillation peak at $z = 0.35$. For some combinations of these data, we show
that there is a clear departure from the standard $\Lambda$CDM model at
intermediary redshifts, although a non-evolving dark energy component ($dw/dz =
0$) cannot be ruled out by these data. The approach developed here may be
useful to probe a possible evolving dark energy component when applied to
upcoming observational data.
