Modified Gravity Constraints from the Full Shape Modeling of Clustering Measurements from DESI 2024

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 datasets. We first consider modified gravity (MG) parametrization in flat ΛCDM and w0waCDM 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 in the 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 dynamical dark energy with w0>−1 and wa<0. We then use binned forms in the two backgrounds starting with two bins in redshift and then combining them with two bins in scale for a total of 4 and 8 MG parameters, respectively. All MG parameters are found consistent with GR. We also find that the tension reported for Σ0 with GR when using Planck PR3 goes away when we use the recent LoLLiPoP+HiLLiPoP likelihoods. As noted previously, this seems to indicate that the tension is related to the CMB lensing anomaly in PR3 which is also resolved when using these likelihoods. We then constrain the class of Horndeski theory in the effective field theory of dark energy. We consider both EFT-basis and α-basis. Assuming a power law parametrization for the 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 DESI(FS+BAO)+DESY5SN+CMB in a ΛCDM background. Similar results are obtained when using the α-basis, where we constrain cM<1.14, and are all consistent with General Relativity.