Does quartessence ease cosmic tensions?
Abstract
Tensions between cosmic microwave background observations and the growth of the largescale structure inferred from latetime probes pose a serious challenge to the concordance ΛCDM cosmological model. Stateoftheart data from the Planck satellite predicts a higher rate of structure growth than what preferred by lowredshift observables. Such tension has hitherto eluded conclusive explanations in terms of straightforward modifications to ΛCDM, e.g. the inclusion of massive neutrinos or a dynamical dark energy component. Here, we investigate models of 'quartessence'  a single dark component mimicking both dark matter and dark energy  whose nonvanishing sound speed inhibits structure growth at late times on scales smaller than its corresponding Jeans' length. In principle, this could reconcile high and lowredshift observations. We put this hypothesis to test against temperature and polarisation spectra from the latest Planck release, SDSS DR12 measurements of baryon acoustic oscillations and redshiftspace distortions, and cosmic shear correlation functions from KiDS. This the first time that any specific model of quartessence is applied to actual data. We show that, if we naïvely apply ΛCDM nonlinear prescription to quartessence, the combined data sets allow for tight constraints on the model parameters. Apparently, quartessence alleviates the tension between the total matter fraction, Ω_{m}, and latetime structure clustering, σ_{8}, although in fact the tension is transferred from σ_{8} to the quartessence sound speed parameter. However, we found that this strongly depends upon information from nonlinear scales. Indeed, if we relax this assumption, quartessence models appear still viable. For this reason, we argue that the nonlinear behaviour of quartessence deserves further investigation and may lead to a deeper understanding of the physics of the dark Universe.
 Publication:

Physics of the Dark Universe
 Pub Date:
 January 2019
 DOI:
 10.1016/j.dark.2018.11.008
 arXiv:
 arXiv:1704.06277
 Bibcode:
 2019PDU....23..247C
 Keywords:

 Dark matter;
 Dark energy;
 Alternative models;
 Cosmological tensions;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 8 pages, 6 figures, 1 table