Eva-Maria Mueller: Even BAO alone requires dark energy + cosmology from the last eBOSS data release

Eva-Maria tells us about the cosmological results from the final (cosmology relevant) SDSS/eBOSS data release. eBOSS is a spectroscopic galaxy survey, precisely mapping galaxies, quasars and the Lyman-α forest.

The two key probes are baryon acoustic oscillations (BAO) and redshift space distortions (RSD). BAO acts as a distance ladder, and eBOSS now has measurements of BAO at enough redshifts that their data alone constrains the expansion history of the universe precisely enough to prove the existence of a dark energy component. The RSD measurements probe the growth of structure, but are unable to resolve any tension between weak lensing measurements and the CMB, with their results lying right between the two alternatives, consistent with both.

The distance scale in BAO can also be anchored using constraints from big bang nucleosynthesis (BBN) allowing eBOSS to infer the expansion rate of the universe today without reference to the CMB. Their measurement is consistent with the CMB and inconsistent with the local distance ladder measurements (e.g. SH0ESS).

The BAO, RSD and CMB are all consistent with the time evolution of the (unanchored) supernovae so all these data sets can be combined to give an overall constraint. This gives very tight bounds on any deviations from a cosmological constant in ΛCDM, and on any deviations from a flat geometry within our observable universe.

The next stage in spectroscopic surveys is DESI, and then Euclid. COVID permitting, we should have the first results from DESI within three years.

Eva-Maria: https://www2.physics.ox.ac.uk/contact...
The paper: https://arxiv.org/abs/2007.08991