Breaking CMB degeneracy in dark energy through LSS

TL;DR

This paper explores how combining large scale structure data with CMB measurements can break degeneracies in dark energy models, especially using RSD and power spectrum corrections, to better constrain dark energy parameters.

Contribution

It demonstrates that RSD and quasi-linear power spectrum measurements can distinguish degenerate dark energy models that mimic CMB spectra, providing new constraints on w0 and wa.

Findings

Growth rate differences are about 0.2% at z=0 between models and LCDM.

Matter power spectrum differences reach up to 4.5% at z=1.0 for certain models.

Lower limit on w0 > -1.5 from CMB acoustic peaks.

Abstract

The cosmic microwave background and large scale structure are complementary probes to investigate the early and late time universe. After the current accomplishment of the high accuracies of CMB measurements, accompanying precision cosmology from LSS data is emphasized. We investigate the dynamical dark energy models which can produce the same CMB angular power spectra as that of the LCDM model with less than a sub-percent level accuracy. If one adopts the dynamical DE models using the so-called Chevallier-Polarski-Linder (CPL) parametrization, w = w0 + wa(1-a), then one obtains models (w0,wa)= (-0.8,-0.767), (-0.9,-0.375), (-1.1,0.355), (-1.2,0.688) named as M8, M9, M11, and M12, respectively. The differences of the growth rate, f which is related to the redshift space distortions (RSD) between different DE models and the LCDM model are about 0.2% only at z=0. The difference of f between M8 (M9, M11, M12) and the LCDM model becomes maximum at z ~ 0.25 with -2.4 (-1.2, 1.2, 2.5)%. This is a scale-independent quantity. One can investigate the one-loop correction of the matter power spectrum of each model using the standard perturbation theory in order to probe the scale-dependent quantity in the quasi-linear regime ({\it i.e.} k < 0.4 h/Mpc). The differences in the matter power spectra including the one-loop correction between M8 (M9, M11, M12) and the LCDM model for k= 0.4 h/Mpc scale are 1.8 (0.9, 1.2, 3.0)% at z=0, 3.0 (1.6, 1.9, 4.2)% at z=0.5, and 3.2 (1.7, 2.0, 4.5)% at z=1.0. The bigger departure from -1 of w0, the larger the difference in the power spectrum. Thus, one should use both the RSD and the quasi-linear observable in order to discriminate a viable DE model among a slew of models which are degenerated in CMB. Also we obtain the lower limit on w0 > -1.5 from the CMB acoustic peaks and this will provide the useful limitation on phantom models.