DES Y1 results: Splitting growth and geometry to test Lambda CDM

Abstract

We analyze Dark Energy Survey (DES) data to constrain a cosmological model where a subset of parameters-focusing on Omega(m)-are split into versions associated with structure growth (e.g., Omega(grow)(m)) and expansion history (e.g., Omega(geo)(m)). Once the parameters have been specified for the Lambda CDM cosmological model, which includes general relativity as a theory of gravity, it uniquely predicts the evolution of both geometry (distances) and the growth of structure over cosmic time. Any inconsistency between measurements of geometry and growth could therefore indicate a breakdown of that model. Our growth-geometry split approach therefore serves both as a (largely) model-independent test for beyond-Lambda CDM physics, and as a means to characterize how DES observables provide cosmological information. We analyze the same multiprobe DES data as [Phys. Rev. Lett. 122, 171301 (2019)] : DES Year 1 (Y1) galaxy clustering and weak lensing, which are sensitive to both growth and geometry, as well as Y1 BAO and Y3 supernovae, which probe geometry. We additionally include external geometric information from BOSS DR12 BAO and a compressed Planck 2015 likelihood, and external growth information from BOSS DR12 RSD. We find no significant disagreement with Omega(grow)(m) = Omega(geo)(m). When DES and external data are analyzed separately, degeneracies with neutrino mass and intrinsic alignments limit our ability to measure Omega(grow)(m), but combining DES with external data allows us to constrain both growth and geometric quantities. We also consider a parametrization where we split both Omega(m) and w, but find that even our most constraining data combination is unable to separately constrain Omega(grow)(m) and w(grow). Relative to Lambda CDM, splitting growth and geometry weakens bounds on sigma(8) but does not alter constraints on h.