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We present constraints on extensions of the minimal cosmological models dominated by dark matter and dark energy, ΛCDM and wCDM, by using a combined analysis of galaxy clustering and weak gravitational lensing from the first-year data of the Dark Energy Survey (DES Y1) in combination with external data. We consider four extensions of the minimal dark energy-dominated scenarios: (1) nonzero curvature Ω k , (2) number of relativistic species N eff different from the standard value of 3.046, (3) time-varying equationof-state of dark energy described by the parameters w 0 and w a (alternatively quoted by the values at the T. M. C. ABBOTT et al. PHYS. REV. D 99, 123505 (2019) 123505-2 pivot redshift, w p , and w a), and (4) modified gravity described by the parameters μ 0 and Σ 0 that modify the metric potentials. We also consider external information from Planck cosmic microwave background measurements; baryon acoustic oscillation measurements from SDSS, 6dF, and BOSS; redshift-space distortion measurements from BOSS; and type Ia supernova information from the Pantheon compilation of datasets. Constraints on curvature and the number of relativistic species are dominated by the external data; when these are combined with DES Y1, we find Ω k ¼ 0.0020 þ0.0037 −0.0032 at the 68% confidence level, and the upper limit N eff < 3.28ð3.55Þ at 68% (95%) confidence, assuming a hard prior N eff > 3.0. For the timevarying equation-of-state, we find the pivot value ðw p ; w a Þ ¼ ð−0.91 þ0.19 −0.23 ; −0.57 þ0.93 −1.11 Þ at pivot redshift z p ¼ 0.27 from DES alone, and ðw p ; w a Þ ¼ ð−1.01 þ0.04 −0.04 ; −0.28 þ0.37 −0.48 Þ at z p ¼ 0.20 from DES Y1 combined with external data; in either case we find no evidence for the temporal variation of the equation of state. For modified gravity, we find the present-day value of the relevant parameters to be Σ 0 ¼ 0.43 þ0.28 −0.29 from DES Y1 alone, and ðΣ 0 ; μ 0 Þ ¼ ð0.06 þ0.08 −0.07 ; −0.11 þ0.42 −0.46 Þ from DES Y1 combined with external data. These modified-gravity constraints are consistent with predictions from general relativity.

We explore the impact of an update to the typical approximation for the shape noise term in the analytic covariance matrix for cosmic shear experiments that assumes the absence of survey boundary and mask effects. We present an exact expression for the number of galaxy pairs in this term based on the survey mask, which leads to more than a factor of three increase in the shape noise on the largest measured scales for the Kilo-Degree Survey (KIDS-450) real-space cosmic shear data. We compare the result of this analytic expression to several alternative methods for measuring the shape noise from the data and find excellent agreement. This update to the covariance resolves any internal model tension evidenced by the previously large cosmological best-fit χ 2 for the KiDS-450 cosmic shear data. The best-fit χ 2 is reduced from 161 to 121 for 118 degrees of freedom. We also apply a correction to how the multiplicative shear calibration uncertainty is included in the covariance. This change shifts the inferred amplitude of the correlation function to higher values. We find that this improves agreement of the KiDS-450 cosmic shear results with Dark Energy Survey Year 1 and Planck results.

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We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark-matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early and late-time probes of the Universe. We investigate how the conversion affects key cosmological observables such as the cosmic microwave background (CMB) temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, Planck-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has