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. $\Omega_m^{\rm grow}$) and expansion history (e.g. $\Omega_m^{\rm geo}$). 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 growthgeometry split approach therefore serves as both a (largely) modelindependent 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 arXiv:1811.02375 : 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 $\Omega_m^{\rm grow}=\Omega_m^{\rm geo}$. When DES and external data are analyzed separately, degeneracies with neutrino mass and intrinsic alignments limit our ability to measure $\Omega_m^{\rm grow}$, but combining DES with external data allows us to constrain both growth and geometric quantities. We also consider a parameterization where we split both $\Omega_m$ and $w$, but find that even our most constraining data combination is unable to separately constrain $\Omega_m^{\rm grow}$ and $w^{\rm grow}$. Relative to $\Lambda$CDM, splitting growth and geometry weakens bounds on $\sigma_8$ but does not alter constraints on $h$.
 Publication:

arXiv eprints
 Pub Date:
 October 2020
 arXiv:
 arXiv:2010.05924
 Bibcode:
 2020arXiv201005924M
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 34 pages, 18 figures, data available upon request