Model independent evidence for dark energy evolution from Baryon Acoustic Oscillations (1406.2209v3)

Abstract: Baryon Acoustic Oscillations (BAO) allow us to determine the expansion history of the Universe, thereby shedding light on the nature of dark energy. Recent observations of BAO's in the SDSS DR9 and DR11 have provided us with statistically independent measurements of $H(z)$ at redshifts of 0.57 and 2.34, respectively. We show that these measurements can be used to test the cosmological constant hypothesis in a model independent manner by means of an improved version of the $Om$ diagnostic. Our results indicate that the SDSS DR11 measurement of $H(z) = 222 \pm 7$ km/sec/Mpc at $z = 2.34$, when taken in tandem with measurements of $H(z)$ at lower redshifts, imply considerable tension with the standard $\Lambda$CDM model. Our estimation of the new diagnostic $Omh^2$ from SDSS DR9 and DR11 data, namely $Omh^2 \approx 0.122 \pm 0.01$, which is equivalent to $\Omega_{0m}h^2$ for the spatially flat $\Lambda$CDM model, is in tension with the value $\Omega_{0m}h^2 = 0.1426 \pm 0.0025$ determined for $\Lambda$CDM from Planck+WP. This tension is alleviated in models in which the cosmological constant was dynamically screened (compensated) in the past. Such evolving dark energy models display a pole in the effective equation of state of dark energy at high redshifts, which emerges as a smoking gun test for these theories.

• The paper presents a model-independent evaluation using the Om diagnostic to expose significant tensions with the ΛCDM framework.
• It reports key measurements including H(z)=222±7 km/s/Mpc at z=2.34 and an updated Omh² value of 0.122±0.01, differing from Planck estimates.
• The evidence implies potential dark energy evolution, suggesting the need to revise cosmic expansion models and explore alternative theories.

Evidence for the Evolution of Dark Energy from Baryon Acoustic Oscillations

This paper examines the implications of recent measurements of Baryon Acoustic Oscillations (BAO), focusing on the expansion history of the Universe and the nature of dark energy (DE). Utilizing datasets from SDSS DR9 and DR11, the authors scrutinize the cosmological constant hypothesis through the lens of a model-independent approach, proposing an improved version of the $Om$ diagnostic. Their analysis reveals significant tension with the traditional $\Lambda$CDM model, suggesting the evolution of dark energy.

Key Insights and Numerical Evidence

The paper provides a model-independent assessment of dark energy evolution by employing the $Om$ diagnostic on BAO measurements. Notably, measurements indicate an expansion rate, $H(z)=222 \pm 7$ km/sec/Mpc at redshift $z=2.34$, which, when combined with measurements at lower redshifts, suggests inconsistency with the $\Lambda$CDM model traditionally supported by Planck data. The primary result is the estimation of the revised diagnostic, $Omh^2 \approx 0.122 \pm 0.01$, which contrasts sharply with the Planck-derived value $\Omega_{0m}h^2 = 0.1426 \pm 0.0025$ for $\Lambda$CDM. This discrepancy, approximately 2-2.5$\sigma$, hints at potential evolutionary behavior for dark energy, contrary to the standard cosmological constant.

Implications and Theoretical Speculations

The findings imply that the cosmological constant may have been dynamically screened in the past, paving the way for evolving dark energy models. Such models predict a divergence in the effective equation of state at high redshifts, presenting a crucial check for these theories. Practically, these results may necessitate revisiting the assumptions of $\Lambda$CDM, suggesting modifications in our understanding of cosmic expansion, the behavior of large-scale structures, and the growth rate of perturbations. Theoretically, evolving dark energy opens up possibilities for alternative frameworks that include modified gravity theories, such as scalar-tensor models.

Future Developments

The apparent tension between observed BAO data and $\Lambda$CDM poses profound questions about the nature of dark energy. Future research should aim to investigate the robustness of these findings and explore other potential modifications to the standard cosmological model. Development of more precise observational techniques and instruments like the LSST and SKA will be crucial in further probing these anomalies. Moreover, an in-depth analysis of perturbation growth in alternative theories could yield valuable insights. As new data becomes available, both theoretical modeling and observational strategies must evolve to accommodate these intriguing possibilities regarding dark energy and cosmic expansion.