CMB-Galaxy correlation in Unified Dark Matter Scalar Field Cosmologies

TL;DR

This study compares Unified Dark Matter scalar field cosmologies with observational data, showing they are as plausible as LambdaCDM and identifying the sound speed parameter's constraints and potential for future low-redshift surveys.

Contribution

It provides the first detailed cross-correlation analysis between CMB and LSS in UDM models, constraining the sound speed and assessing model viability against observations.

Findings

UDM models are as likely as LambdaCDM based on data.

Upper bound of c_infinity^2 ≤ 0.009 at 95% confidence.

Future low-redshift surveys can better constrain UDM models.

Abstract

We present an analysis of the cross-correlation between the CMB and the large-scale structure (LSS) of the Universe in Unified Dark Matter (UDM) scalar field cosmologies. We work out the predicted cross-correlation function in UDM models, which depends on the speed of sound of the unified component, and compare it with observations from six galaxy catalogues (NVSS, HEAO, 2MASS, and SDSS main galaxies, luminous red galaxies, and quasars). We sample the value of the speed of sound and perform a likelihood analysis, finding that the UDM model is as likely as the LambdaCDM, and is compatible with observations for a range of values of c_\infinity (the value of the sound speed at late times) on which structure formation depends. In particular, we obtain an upper bound of c_\infinity^2 \leq 0.009 at 95% confidence level, meaning that the LambdaCDM model, for which c_\infinity^2 = 0, is a good fit to the data, while the posterior probability distribution peaks at the value c_\infinity^2=10^(-4) . Finally, we study the time dependence of the deviation from LambdaCDM via a tomographic analysis using a mock redshift distribution and we find that the largest deviation is for low-redshift sources, suggesting that future low-z surveys will be best suited to constrain UDM models.