Princeton University Gravity Group Lunch Seminar

Phenomenological parameterization of the perturbed Einstein's equations has become an important route to testing General Relativity (GR) at cosmological scales. This is often done by constraining a pair of modified gravity (MG) parameters. We explore here constraints on one MG parameter at a time while fixing the other at its GR value. We find cases with a stronger tension with GR than two-MG-parameter approaches. For example, models with (μ=1, η) and (μ, η=1) exhibit a 3.9-σ departure from their GR values when using Planck18+SNe+BAO data. Using a Bayesian model selection analysis, we find one-parameter MG models that are moderately favored over ΛCDM when using all dataset combinations except CMB Lensing and DES data. Namely, Planck shows a moderate tension with GR that only increases when adding BAO, SNe and RSD. However, adding Planck CMB Lensing or DES data respectively diminishes or removes these tensions. The results show a new overall dichotomy between Planck and large-scale structure datasets when performing consistency tests with GR, which may be due to systematic effects, lack of constraining power, or the problems with the underlying theory.