Modified gravity constraints from the full shape modeling of clustering measurements from DESI 2024

Abstract

We present cosmological constraints on deviations from general relativity (GR) from the first-year of clustering observations from the Dark Energy Spectroscopic Instrument (DESI) in combination with other available datasets including the CMB data from Planck with CMB-lensing from Planck and ACT, BBN constraints on the physical baryon density, the galaxy weak lensing and clustering from DESY3 and supernova data from DESY5. We first consider the μ(a,k)–Σ(a,k) modified gravity (MG) parameterization (as well as η(a,k)) in a ΛCDM and a w0waCDM cosmological backgrounds. Using a functional form for time-only evolution gives μ0 = 0.11+0.44-0.54 from DESI(FS+BAO)+BBN and a wide prior on ns. Using DESI(FS+BAO)+CMB+DESY3+DESY5-SN, we obtain μ0 = 0.05 ± 0.22 and Σ0 = 0.008 ± 0.045 and similarly μ0 = 0.02+0.19-0.24 and η0 = 0.09+0.36-0.60, in an ΛCDM background. In w0waCDM we obtain μ0 = -0.24+0.32-0.28 and Σ0 = 0.006 ± 0.043, consistent with GR, and we still find a preference of the data for a dynamical dark energy with w0 > -1 and wa < 0. Using functional dependencies in both time and scale gives μ0 and Σ0 with a same level of precision as above but other scale MG parameters remain hard to constrain. We then move to binned parameterizations in a ΛCDM background starting with two bins in redshift and obtain, μ1 = 1.02 ± 0.13, μ2 = 1.04 ± 0.11, Σ1 = 1.021 ± 0.029 and Σ2 = 1.022+0.027-0.023, all consistent with the unity value of GR in the binning formalism. We then extend the analysis to combine two bins in redshift and two in scale giving 8 MG parameters that we find all consistent with GR. We note that we find here that the tension reported in previous studies about Σ0 being inconsistent with GR when using Planck PR3 data goes away when we use the recent LoLLiPoP+HiLLiPoP likelihoods. As noted in previous studies, this seems to indicate that the tension is indeed related to the CMB lensing anomaly in PR3 which is also resolved when using the recent likelihoods. We then constrain the class of Horndeski theory in the effective field theory of dark energy approach. We consider both EFT-basis and α-basis in the analysis. Assuming a power law parameterization for the EFT function Ω, which controls non-minimal coupling, we obtain Ω0 = 0.012+0.001-0.012 and s0 = 0.996+0.54-0.20 from the combination of DESI(FS+BAO)+DESY5SN+CMB in a ΛCDM background, which are consistent with GR. Similar results are obtained when using the α-basis and assuming no-braiding (αB = 0) giving cM < 1.14 at 95% CL in a ΛCDM background, also in agreement with GR. However, we see a mild yet consistent indication for cB > 0 when αB is allowed to vary which will require further study to determine whether this is due to systematics or new physics.