Day 1491

Friday.

1810.10552
Non-parametric cosmology with cosmic shear
Taylor, Kitching, McEwen

Present a method to measure the growth of structure and the background geometry of the Universe -- which no a priori assumption about the underlying cosmological model.  Using CFHTLenS shear data, simultaneously reconstruct the lensing amplitude, the linear intrinsic alignment amplitude, the redshift evolving matter power spectrum, P(k,z), and the co-moving distance, r(z).  Find that lensing predominately constrains a single global power spectrum amplitude and several co-moving distance bins.  The approach can localize precise scales and redshifts where LCDM fails -- if any.  Find that below z=0.4, the measured co-moving distance r(z) is higher than that expected from the Planck LCDM cosmology by ~1.5 sigma, while at higher redshifts, the reconstruction is fully consistent; this is precisely what we would expect if the reported discrepancy between high and low-redshift measurements of H_0 is physical.  To validate the reconstruction, compare LCDM parameter constraints form the standard cosmic shear likelihood analysis to those found by fitting to the non-parametric information and find good agreement.


1810.10547
The end of cosmic growth
Linder, Polarski

The growth of large scale structure is a battle between gravitational attraction and cosmic acceleration.  Investigate the future behavior of cosmic growth under both GR and modified gravity during prolonged acceleration, deriving analytic asymptotic behaviors and showing that gravity generally loses and growth ends.  Also note the 'why now' problem is equally striking when viewed in terms of the shut down of growth.  For many models inside GR the gravitational growth index \gamma also shows today as a unique time between constant behavior in the past and a higher asymptotic value in the future.  Interestingly, while f(R) models depart in this respect dramatically from GR today and in the recent past, their growth indices are identical in the asymptotic future and past.


1810.10553
Impact of weak lensing mass calibration on eROSITA galaxy cluster cosmological studies -- a forecast
Grandis, Mohr, et al

Forecast the impact of WL cluster mass calibration on the cosmo constraints that will be derived using the X-ray selected galaxy cluster counts from the upcoming eROSITA survey.  To this end, produce a realistic mock cluster catalog within a fiducial cosmology, where each cluster has an observed eROSITA count rate, redshift and gravitational WL tangential shear profile.  The shear profiles are produced to mimic either those from the DES or the future Euclid and LSST surveys.  Using a count rate selection, generate a baseline cosmology catalog that contains 13k clusters over 14,892 deg^2 of extragalactic sky.  Low mass clusters are excluded from this sample using raised count rate thresholds at low redshift.  Analyze the mock cluster sample using a prototype of the eROSITA cosmo analysis pipeline.  Forecast parameter uncertainties for Omega_M, sigma* and w are 0.23 (0.016), 0.038 (0.012), and 0.085 (0.074), respectively, when adopting DES WL (Euclid+LSST WL).  Explore the parameter sensitivities in the experiment and identify a degeneracy between the distance--redshift relation and the parameters of the observable--mass scaling relation that ultimately limits the impact of the WL calibration on the w constraints, and show how this degeneracy can be broken by the inclusion of BAO measurements from DESI, allowing a determination of w to 0.047.  If Planck CMB priors are included, Omega_m and sigma_8 can be determined to 0.005 and 0.007, respectively, while putting an upper limit on the summed neutrino mass sum m_nu< 0.211 eV (at 95%).  Finally, show that if systematic uncertainties at the group mass scale can be controlled, an expanded eROSITA sample with 43k objects with Euclid+LSST WL analysis would determine Omega_m and sigma_8 to 0.007 and w to 0.056.