CMB tensions with low-redshift $H_0$ and $S_8$ measurements: impact of a redshift-dependent type-Ia supernovae intrinsic luminosity

TL;DR

This work investigates the tensions between early-universe (CMB) and late-time (local) measurements of cosmological parameters, notably $H_0$ and $S_8$, within and beyond ΛCDM. It extends the analysis by reconstructing a redshift-dependent dark energy equation of state $w(z)$ and by introducing redshift-dependent SNIa intrinsic luminosity corrections tied to star formation rate and metallicity, while incorporating BAO data. The key finding is that allowing a generalized late-time expansion history (especially $w(z)$CDM) and including SNIa systematics can significantly alleviate, and in some cases remove, the $H_0$ tension when BAO data are not included, but BAO data re-establish the low $H_0$ values; the $S_8$ tension remains largely unaffected. The results suggest that either new physics beyond late-time dark energy or additional unaccounted systematics (notably in BAO) are needed to fully reconcile high- and low-redshift cosmological constraints.

Abstract

With the recent increase in precision of our cosmological datasets, measurements of $Λ$CDM model parameter provided by high- and low-redshift observations started to be in tension, i.e., the obtained values of such parameters were shown to be significantly different in a statistical sense. In~this work we tackle the tension on the value of the Hubble parameter, $H_0$, and the weighted amplitude of matter fluctuations, $S_8$, obtained from local or low-redshift measurements and from cosmic microwave background (CMB) observations. We combine the main approaches previously used in the literature by extending the cosmological model and accounting for extra systematic uncertainties. With such analysis we aim at exploring non standard cosmological models, implying deviation from a cosmological constant driven acceleration of the Universe expansion, in the presence of additional uncertainties in measurements. In more detail, we reconstruct the Dark Energy equation of state as a function of redshift, while we study the impact of type-Ia supernovae (SNIa) redshift-dependent astrophysical systematic effects on these tensions. We consider a SNIa intrinsic luminosity dependence on redshift due to the star formation rate in its environment, or the metallicity of the progenitor. We find that the $H_0$ and $S_8$ tensions can be significantly alleviated, or~even removed, if we account for varying Dark Energy for SNIa and CMB data. However, the tensions remain when we add baryon acoustic oscillations (BAO) data into the analysis, even after the addition of extra SNIa systematic uncertainties. This points towards the need of either new physics beyond late-time Dark Energy, or other unaccounted systematic effects (particulary in BAO measurements), to fully solve the present tensions.

Figures (6)

• Figure S1: 68% and 95% confidence level contours for $\Omega_m$ and $H_0$ for the dark energy models explored ($\Lambda$CDM in blue, constant $w$ in yellow, and binned $w(z)$ in red) when no systematics are included in the analysis of the SNIa dataset. The data used are Planck + BAO + SNIa with SNIa datasets given by JLA (left panel) and Pantheon (right panel).
• Figure S2: 68% and 95% confidence level contours for $\Omega_M$ and $H_0$ for the dark energy models explored ($\Lambda$CDM in blue, constant $w$ in yellow, and binned $w(z)$ in red) when star formation rate systematic effects are included in the analysis of the SNIa dataset. The data used are Planck+BAO+SNIa with SNIa datasets given by JLA (left panel) and Pantheon (right panel).
• Figure S3: 68% and 95% confidence level contours for $\Omega_M$ and $H_0$ for the dark energy models explored ($\Lambda$CDM in blue, constant $w$ in yellow, and binned $w(z)$ in red) when metallicity systematic effects are included in the analysis of the SNIa dataset. The data used are Planck + BAO + SNIa with SNIa datasets given by JLA (left panel) and Pantheon (right panel).
• Figure S4: Reconstruction of the EoS in the $w(z)$CDM analysis. The points are the mean values of the posterior distributions obtained from the analysis, with the error bars corresponding to the 68% confidence limits. The results are shown for all the systematic models analyzed, i.e., SFR (red lines), metallicity (yellow line) and without any systematic effect (black lines). The data used are Planck + BAO + SNIa with SNIa datasets given by JLA (left panel) and Pantheon (right panel). Please note that the binned values of $w(z)$ are taken at the same redshifts in all three cases considered, with their spread in redshift artificially included only for better visualization.
• Figure S5: Visualization of the $H_0$ tension between Planck+SNIa and the local measurement. The error bars correspond to the 68% errors for the different cases explored in this paper, while the gray band highlights the $1\sigma$ bound of the SH0eS collaboration. The data used are Planck + BAO + SNIa with SNIa datasets given by JLA (left panel) and Pantheon (right panel).