Tom Shanks, Lucy Hogarth, Nigel Metcalfe, Durham University, UK)

There has been much discussion of the tension between the values of Hubble's Constant $H_0$ implied by the distance scale and fits to the microwave background's primordial power spectrum. While the latter is fitted by standard cosmological models with $H_0=67.4\pm0.5$kms$^{-1}$Mpc$^{-1}$, the distance scale gives $H_0=73.45\pm1.66$kms$^{-1}$Mpc$^{-1}$, an $\approx10$%, $\approx3.5\sigma$ discrepancy. Here we first show that GAIA parallax distances of Milky Way Cepheids may be between $\approx7-18$% larger than previously estimated, with the potential to produce a corresponding reduction in the value of $H_0$. Then we show that the existence of an $\approx150$h$^{-1}$Mpc `Local Hole' in the galaxy distribution around our position implies an outflow of $\approx500$kms$^{-1}$ averaging over direction. Accounting for this in the recession velocities of SNIa standard candles out to $z\approx0.1$ reduces $H_0$ by a further $\approx1.8$%, while maintaining reasonable consistency with the supernova Hubble diagram. Combining this result with even an $\approx7$% increase in the Cepheid distance scale due to GAIA implies an $\approx9$% reduction in the value of the Hubble Constant, decreasing from $H_0\approx73.45$ to 67.6 kms$^{-1}$Mpc$^{-1}$. This would leave the distance scale and Planck Cosmic Microwave Background values entirely consistent, thus potentially relieving the previous $H_0$ tension.

Joshua A. Kable, Graeme E. Addison, Charles L. Bennett

We revisit the degeneracy between the Hubble constant, $H_0$, and matter density, $\Omega_m$, for current cosmic microwave background (CMB) observations within the standard $\Lambda CDM$ model. We show that Planck, Wilkinson Microwave Anisotropy Probe (WMAP), South Pole Telescope (SPT), and Atacama Cosmology Telescope Polarimeter (ACTPol) temperature power spectra produce different values of the exponent $x$ from minimizing the variance of the product $\Omega_mH_0^x$. The distribution of $x$ from the different data sets does not follow the Markov Chain Monte Carlo (MCMC) best-fit values for $H_0$ or $\Omega_m$. Particularly striking is the difference between Planck multipoles $\ell\leq800$ ($x=2.81$), and WMAP ($x = 2.94$), despite very similar best-fit cosmologies. We use a Fisher matrix analysis to show that, in fact, this range in exponent values is exactly as expected in $\Lambda CDM$ given the multipole coverage and power spectrum uncertainties for each experiment. We show that the difference in $x$ from the Planck $\ell \leq 800$ and WMAP data is explained by a turning point in the relationship between $x$ and the maximum effective multipole, at around $\ell=700$. The value of $x$ is determined by several physical effects, and we highlight the significant impact of gravitational lensing for the high-multipole measurements. Despite the spread of $H_0$ values from different CMB experiments, the experiments are consistent with their sampling of the $\Omega_m-H_0$ degeneracy and do not show evidence for the need for new physics or for the presence of significant underestimated systematics according to these tests. The Fisher calculations can be used to predict the $\Omega_m-H_0$ degeneracy of future experiments.

Sebastian Garcia-Saenz, Kurt Hinterbichler, Rachel A. Rosen

We find and classify the ${\cal N}=1$ SUSY multiplets on AdS$_4$ which contain partially massless fields. We do this by studying the non-unitary representations of the $d=3$ superconformal algebra of the boundary. The simplest super-multiplet which contains a partially massless spin-2 particle also contains a massless photon, a massless spin-$3/2$ particle and a massive spin-$3/2$ particle. The gauge parameters form a Wess-Zumino super-multiplet which contains the gauge parameters of the photon, the partially massless graviton, and the massless spin-$3/2$ particle. We find the AdS$_4$ action and SUSY transformations for this multiplet. More generally, we classify new types of shortening conditions that can arise for non-unitary representations of the $d=3$ superconformal algebra.

Wenzer Qin, Kimberly K. Boddy, Marc Kamionkowski, Liang Dai

We discuss the theory of pulsar-timing and astrometry probes of a stochastic gravitational-wave background with a recently developed "total-angular-momentum'" (TAM) formalism for cosmological perturbations. We review the formalism, emphasizing in particular the features relevant for this work. We describe the observables we consider (which we take to be the pulsar redshift and stellar angular displacement). We derive from the TAM approach angular power spectra for the observables and from them derive angular auto- and cross-correlation functions. We provide the full set of power spectra and correlation functions not only for the standard transverse-traceless propagating degrees of freedom in general relativity, but also for the four additional non-Einsteinian polarizations that may arise in alternative-gravity theories. We clarify the range of gravitational-wave frequencies that can be probed with pulsar timing and astrometry; speculate on the possibility to reconstruct the local three-dimensional metric perturbation with combined angular and time-sequence information; comment on the importance of testing the chirality of the gravitational-wave background; and describe briefly how to seek the type of power asymmetry that might arise if the signal is dominated by a handful of nearby sources. We also provide in an Appendix a simple re-derivation of the power spectra from the plane-wave formalism.

Y. Omori, E. Baxter, C. Chang, D. Kirk, A. Alarcon, G. M. Bernstein, L. E. Bleem, R. Cawthon, A. Choi, R. Chown, T. M. Crawford, C. Davis, J. De Vicente, J. DeRose, S. Dodelson, T. F. Eifler, P. Fosalba, O. Friedrich, M. Gatti, E. Gaztanaga, T. Giannantonio, D. Gruen, W. G. Hartley, G. P. Holder, B. Hoyle, D. Huterer, B. Jain, M. Jarvis, E. Krause, N. MacCrann, R. Miquel, J. Prat, M. M. Rau, C. L. Reichardt, E. Rozo, S. Samuroff, C. Sánchez, L. F. Secco, E. Sheldon, G. Simard, M. A. Troxel, P. Vielzeuf, R. H. Wechsler, J. Zuntz, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, S. Avila, K. Aylor, B. A. Benson, E. Bertin, S. L. Bridle, D. Brooks, D. L. Burke, J. E. Carlstrom, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, C. L. Chang, H-M. Cho, A. T. Crites, M. Crocce, et al. (76 additional authors not shown)

We cross-correlate galaxy weak lensing measurements from the Dark Energy Survey (DES) year-one (Y1) data with a cosmic microwave background (CMB) weak lensing map derived from South Pole Telescope (SPT) and Planck data, with an effective overlapping area of 1289 deg$^{2}$. With the combined measurements from four source galaxy redshift bins, we reject the hypothesis of no lensing with a significance of $10.8\sigma$. When employing angular scale cuts, this significance is reduced to $6.8\sigma$, which remains the highest signal-to-noise measurement of its kind to date. We fit the amplitude of the correlation functions while fixing the cosmological parameters to a fiducial $\Lambda$CDM model, finding $A = 0.99 \pm 0.17$. We additionally use the correlation function measurements to constrain shear calibration bias, obtaining constraints that are consistent with previous DES analyses. Finally, when performing a cosmological analysis under the $\Lambda$CDM model, we obtain the marginalized constraints of $\Omega_{\rm m}=0.261^{+0.070}_{-0.051}$ and $S_{8}\equiv \sigma_{8}\sqrt{\Omega_{\rm m}/0.3} = 0.660^{+0.085}_{-0.100}$. These measurements are used in a companion work that presents cosmological constraints from the joint analysis of two-point functions among galaxies, galaxy shears, and CMB lensing using DES, SPT and Planck data.

T. M. C. Abbott, F. B. Abdalla, S. Avila, M. Banerji, E. Baxter, K. Bechtol, M. R. Becker, E. Bertin, J. Blazek, S. L. Bridle, D. Brooks, D. Brout, D. L. Burke, A. Campos, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, R. Cawthon, C. Chang, A. Chen, M. Crocce, C. E. Cunha, L. N. da Costa, C. Davis, J. De Vicente, J. DeRose, S. Desai, E. Di Valentino, H. T. Diehl, J. P. Dietrich, S. Dodelson, P. Doel, A. Drlica-Wagner, T. F. Eifler, J. Elvin-Poole, A. E. Evrard, E. Fernandez, A. Ferté, B. Flaugher, P. Fosalba, J. Frieman, J. García-Bellido, D. W. Gerdes, T. Giannantonio, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, W. G. Hartley, D. L. Hollowood, K. Honscheid, B. Hoyle, D. Huterer, B. Jain, T. Jeltema, M. W. G. Johnson, M. D. Johnson, et al. (54 additional authors not shown)

We present constraints on extensions of the minimal cosmological models dominated by dark matter and dark energy, $\Lambda$CDM and $w$CDM, 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 $\Omega_k$, 2) number of relativistic species $N_{\rm eff}$ different from the standard value of 3.046, 3) time-varying equation-of-state of dark energy described by the parameters $w_0$ and $w_a$ (alternatively quoted by the values at the pivot redshift, $w_p$, and $w_a$), and 4) modified gravity described by the parameters $\mu_0$ and $\Sigma_0$ that modify the metric potentials. We also consider external information from Planck CMB measurements; BAO measurements from SDSS, 6dF, and BOSS; RSD measurements from BOSS; and SNIa information from the Pantheon compilation. Constraints on curvature and the number of relativistic species are dominated by the external data; when these are combined with DES Y1, we find $\Omega_k=0.0020^{+0.0037}_{-0.0032}$ at the 68\% confidence level, and $N_{\rm eff}<3.28\, (3.55)$ at 68\% (95\%) confidence. For the time-varying equation-of-state, we find the pivot value $(w_p, w_a)=(-0.91^{+0.19}_{-0.23}, -0.57^{+0.93}_{-1.11})$ at pivot redshift $z_p=0.27$ from DES alone, and $(w_p, w_a)=(-1.01^{+0.04}_{-0.04}, -0.28^{+0.37}_{-0.48})$ at $z_p=0.20$ 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 $\Sigma_0= 0.43^{+0.28}_{-0.29}$ from DES Y1 alone, and $(\Sigma_0, \mu_0)=(0.06^{+0.08}_{-0.07}, -0.11^{+0.42}_{-0.46})$ from DES Y1 combined with external data, consistent with predictions from GR.

Alejandro Aviles, Jorge L. Cervantes-Cota, David F. Mota

We present a formalism to study screening mechanisms in modified theories of gravity via perturbative methods in cosmological scenarios. By a redefinition of the scalar field degree of freedom we are able to recast the Jordan and Einstein frames perturbative equations in a single, already known framework. In spite of the fact that screening mechanisms are nonlinear phenomena, our perturbation approach give us an analytical tool to probe and understand features in screening mechanisms. This allow us to compare several theoretical models and to recognize patterns which can be used to differentiate models and their screening mechanisms. In particular, we find anti-screening features in the Symmetron model. In opposition, chameleon type theories, both in the Jordan and in the Einstein frame, always present a screening behaviour. Up to third order in perturbation, we find no anti-screening behaviour in theories with a Vainshtein mechanism, such as the DGP and the cubic Galileon.

Adam G. Riess, Stefano Casertano, D'Arcy Kenworthy, Dan Scolnic, Lucas Macri

Shanks et al. (2018) arXiv:1810.02595 make two claims that they argue bring the local measurement and early Universe prediction of H0 into agreement: A) they claim that Gaia DR2 parallax measurements show the geometric calibration of the Cepheid distance scale used to measure H0 to be grossly in error and B) that we live near the middle of an enormous void, further biasing the local measurement of the Hubble constant. We show that the first claim is caused by five erroneous uses of the data: in decreasing order of importance: 1) the use of a distance indicator, main sequence fitting of cluster stars, which is unrelated to the calibration of Cepheids and therefore has no bearing on current measurements of H0; 2) the use of Gaia data for Cepheids that fully saturate the detector, producing unreliable parallaxes; 3) the use of a fixed parallax offset which is known to depend on source magnitude and color but which is derived for sources with extremely different colors and magnitudes; 4) ignoring the uncertainty in this offset; and 5) ignoring the other geometric sources of Cepheid calibration, the distance of the LMC from detached eclipsing binaries and the masers in NGC 4258, which are independent of Milky Way parallaxes. Just resolving the first two of these issues by not using unrelated or saturated data leads to no inconsistency between Gaia parallaxes and the current Cepheid distance scale. The second claim can be refuted 6) because of the increase in chi-squared that the alleged void would entail in SN measurements in the Hubble flow, and 7) because it would represent a 6 sigma fluctuation of cosmic variance between the local and globally measured expansion, requiring us to live in an exceedingly special location.