New null diagnostic customized for reconstructing the properties of dark energy from baryon acoustic oscillations data

Baryon acoustic oscillations (BAO) provide an important standard ruler which can be used to probe the recent expansion history of our Universe. We show how a simple extension of the $Om$ diagnostic, which we call $Om3$, can combine standard ruler information from BAO with standard candle information from type Ia supernovae (SNIa) to yield a powerful novel null diagnostic of the cosmological constant hypothesis. A unique feature of $Om3$ is that it requires minimal cosmological assumptions since its determination does not rely upon prior knowledge of either the current value of the matter density Ω₀ₘ and the Hubble constant H₀ or the distance to the last scattering surface. Observational uncertainties in these quantities, therefore, do not affect the reconstruction of $Om3$. We reconstruct $Om3$ using the Union 2.1 SNIa data set and BAO data from SDSS, WiggleZ and 6dFGS. Our results are consistent with dark energy being the cosmological constant. We show how $Om$ and $Om3$ can be used to obtain accurate model-independent constraints on the properties of dark energy from future data sets such as BigBOSS.