Dark matter component decaying after recombination: Sensitivity to BAO and RSD probes

TL;DR

This study tests a two-component dark matter scenario in which a subdominant fraction $F$ decays after recombination with decay width $Γ$, potentially reconciling high-redshift Planck observations with low-redshift measurements. Using a comprehensive data set that includes Planck CMB data, $H_0$ and cluster counts, and a broad array of BAO and RSD measurements across low to high redshift (including Ly-$\alpha$ BAO), the authors perform MCMC analyses with a modified Boltzmann code to constrain $F$ and $Γ$ alongside standard $\Lambda$CDM parameters. They find that BAO/RSD probes from BOSS DR12 generally prefer $\Lambda$CDM, yielding upper bounds $F\lesssim 0.04$–$0.07$ (2σ) depending on the data combination; Ly-$\alpha$ BAO allows somewhat larger $F$, while introducing a free lensing amplitude $A_L$ makes a nonzero $F$ more favorable, with improvements up to $\sim3.3σ$ in certain data sets. Overall, current cosmological data place tight limits on the DDM fraction, but a few-percent admixture can modestly improve the fit, especially when lensing and high-redshift BAO data are considered; future surveys (DES, Euclid, LSST) and 21 cm intensity mapping could further probe intermediate lifetimes $Γ^{-1}$ and better discriminate this scenario.

Abstract

It has been recently suggested~\cite{Berezhiani:2015yta} that a subdominant fraction of dark matter decaying after recombination may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (Hubble constant, cluster counts) measurements. In this report, we continue our previous study~\cite{Chudaykin:2016yfk} of the decaying dark matter (DDM) model adding all available recent baryon acoustic oscillation (BAO) and redshift space distortions (RSD) measurements. We find, that the BAO/RSD measurements generically prefer the standard $Λ$CDM and combined with other cosmological measurements impose an upper limit on the DDM fraction at the level of $\sim$\,5\,\%, strengthening by a factor of 1.5 limits obtained in \cite{Chudaykin:2016yfk} mostly from CMB data. However, the numbers vary from one analysis to other based on the same Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) galaxy sample. Overall, the model with a few percent DDM fraction provides a better fit to the combined cosmological data as compared to the $Λ$CDM: the cluster counting and direct measurements of the Hubble parameter are responsible for that. The improvement can be as large as 1.5\,$σ$ and grows to 3.3\,$σ$ when the CMB lensing power amplitude ${\rm A_L}$ is introduced as a free fitting parameter.

Figures (11)

• Figure 1: The redshift evolution of $D_A/r_s$ in the $\Lambda$CDM model fitted to the Base data set (solid line) and in the DDM cosmology with reference values $F=0.05$ and $\Gamma=2000$ km/s/Mpc while remaining six standard parameters are kept the same as in $\Lambda$CDM (dashed line). Zhao result is shown by blue boxes with error bars which show $\pm1\sigma$ uncertainties. Chuang likelihood is illustrated by green dots with error bars.
• Figure 2: Same as Fig. \ref{['fig:DA']} but for $D_H/r_s$ evolution.
• Figure 3: Same as Fig. \ref{['fig:DA']} but for $f\sigma_8$ evolution. Zhao data set is absent here because pure BAO measurements do not impose constraints on $f\sigma_8$.
• Figure 4: Same as Fig. \ref{['fig:DA']} but for $\omega_m=\Omega_m\,h^2$ evolution. Zhao data set does not constrain $\omega_m$.
• Figure 5: Posterior distributions ($1\,\sigma$ and $2\,\sigma$ contours) of parameters $F$, $\Gamma$ in DDM model. Tags are described in Table \ref{['tab:sets']}.