Cosmology with the EFTofLSS and BOSS: dark energy constraints and a note on priors

TL;DR

This work analyzes BOSS DR12 full-shape power spectrum multipoles and BAO within ΛCDM, $w$CDM, and the dark-scattering $wA$CDM framework using EFTofLSS with FAST-PT and the BACCO linear emulator, exploring analyses with and without Planck priors on primordial parameters. The authors reproduce known EFT results for ΛCDM, find phantom $w$ in the CMB-free $w$CDM case, and provide the first constraints on the dark-energy–dark-matter interaction parameter $A$ in $wA$CDM, including a 1σ hint of interaction when Planck priors are applied. They show that strong degeneracies between $A$, $A_s$, and nuisance parameters arise in the CMB-free analysis, and that priors on nuisance parameters are highly informative, capable of shifting contours and even cosmological inferences. The results illustrate the potential of EFTofLSS to guide beyond-$\Lambda$CDM analyses with current data and underscore the need for careful treatment of nuisance priors in LSS studies, which has implications for future surveys and model testing.

Abstract

We analyse the BOSS DR12 galaxy power spectrum data jointly with BAO data for three models of dark energy. We use recent measurements using a windowless estimator, and an independent and fast pipeline based on EFTofLSS implemented via the FAST-PT algorithm to compute the redshift-space loop corrections. We accelerate our analysis by using the BACCO linear emulator instead of a Boltzmann solver. We perform two sets of analyses: one with $3σ$ Planck priors on $A_s$ and $n_s$, and another that is CMB-free, without such priors. Firstly, we study $Λ$CDM, reproducing previous results obtained with the same estimator. We find a low value of $A_s$ in the CMB-free case, in agreement with many previous full-shape analyses of the BOSS data. We then study $w$CDM, finding a lower value of the amplitude in the CMB-free run, coupled with a preference for phantom dark energy with $w=-1.17^{+0.12}_{-0.11}$, again in broad agreement with previous results. Finally, we investigate the dark scattering model, which we label $wA$CDM. In the CMB-free analysis, we find a large degeneracy between the interaction strength $A$ and the amplitude $A_s$, hampering measurements of those parameters. On the contrary, in our run with a CMB prior, we are able to constrain the dark energy parameters to be $w=-0.972^{+0.036}_{-0.029}$ and $A = 3.9^{+3.2}_{-3.7}$, which show a 1$σ$ hint of interacting dark energy. This is the first measurement of this parameter and demonstrates the ability of this model to alleviate the $σ_8$ tension. Our analysis can be used as a guide for any model with scale-independent growth. Finally, we study the dependence of the results on the priors of the nuisance parameters and find these priors to be informative, with their broadening creating shifts in the contours. We argue for an in depth study of this issue, which can affect current and forthcoming analyses of LSS data.

Figures (18)

• Figure 1: Marginalized posteriors for the sampled cosmological parameters and $\Omega_m$ and $\sigma_8$ for $\Lambda$CDM for the analysis using only the full-shape power spectrum data. We use $k_{\rm max}=0.20~h/{\rm Mpc}$ for all 3 multipoles. This case mimics the analysis of Philcox and Ivanov (P+I) Philcox:2021main, and solid red lines show the mean of the parameters obtained there, shown in Table III of that reference, demonstrating perfect agreement.
• Figure 2: Marginalized posteriors for the sampled cosmological parameters for $\Lambda$CDM, showing both the analysis with (blue empty contours) and without (orange filled contours) a 3$\sigma$ Planck prior on the primordial parameters (as well as a BBN prior on $\omega_b$). We use $k_{\rm max}=0.20~h/{\rm Mpc}$ for all 3 power spectrum multipoles and use the full-shape data and the BAO measurement. Solid green lines mark the best-fit values from the Planck $\Lambda$CDM analysis, while red lines show the $\sigma_8$ and $S_8$ measured in the fiducial $\Lambda$CDM DES analysis DES:2021bvcSecco:2021vhm.
• Figure 3: Marginalized posteriors for the sampled cosmological parameters for $w$CDM, showing both the analysis with (blue empty contours) and without (orange filled contours) a 3$\sigma$ Planck prior on the primordial parameters (as well as a BBN prior on $\omega_b$). We use $k_{\rm max}=0.20~h/{\rm Mpc}$ for all 3 multipoles and use the full shape data and the BAO measurement. Solid green lines mark the best-fit values from the Planck $\Lambda$CDM analysis while red lines show the $\sigma_8$ and $S_8$ measured in the fiducial $\Lambda$CDM DES analysis DES:2021bvcSecco:2021vhm.
• Figure 4: Marginalized posteriors for the sampled cosmological parameters in the analysis with a Planck prior on the primordial parameters (as well as a BBN prior on $\omega_b$). We use $k_{\rm max}=0.20~h/{\rm Mpc}$ for all 3 multipoles and show both the analysis with the full shape only (FS, blue empty contours) and with both the full shape and the BAO measurement (FS+BAO, orange filled contours). The shape of the $w-A$ contour is due to the physical prior imposed on those parameters, i.e. ${\rm sign}(A)={\rm sign}(1+w)$. Solid green lines mark the best-fit values from Planck $\Lambda$CDM analysis.
• Figure 5: Marginalized posteriors for the dark energy parameters and the derived parameters $S_8$, $\sigma_8$ and $\Omega_m$, for the same analysis of Fig. \ref{['fig:baseline_BAO']}. We also show the values of $S_8$ and $\sigma_8$ measured in the fiducial $\Lambda$CDM DES analysis DES:2021bvcSecco:2021vhm with red solid lines, demonstrating our good agreement with those experiments.