José Luis Bernal, Licia Verde, Raul Jimenez, Marc Kamionkowski, David Valcin, Benjamin D. Wandelt

The distance ladder using supernovae yields higher values of the Hubble constant $H_0$ than those inferred from measurements of the cosmic microwave background (CMB) and galaxy surveys, a discrepancy that has come to be known as the `Hubble tension'. This has motivated the exploration of extensions to the standard cosmological model in which higher values of $H_0$ can be obtained from CMB measurements and galaxy surveys. The trouble, however, goes beyond $H_0$; such modifications affect other quantities, too. In particular, their effects on cosmic times are usually neglected. We explore here the implications that measurements of the age $t_{\rm U}$ of the Universe, such as a recent inference from the age of the oldest globular clusters, can have for potential solutions to the $H_0$ tension. The value of $H_0$ inferred from the CMB and galaxy surveys is related to the sound horizon at CMB decoupling (or at radiation drag), but it is also related to the matter density and to $t_{\rm U}$. Given this observation, we show how model-independent measurements may support or disfavor proposed new-physics solutions to the Hubble tension. Finally, we argue that cosmological measurements today provide constraints that, within a given cosmological model, represent an over-constrained system, offering a powerful diagnostic tool of consistency. We propose the use of ternary plots to simultaneously visualize independent constraints on key quantities related to $H_0$ like $t_{\rm U}$, the sound horizon at radiation drag, and the matter density parameter. We envision that this representation will help find a solution to the trouble of and beyond $H_0$.

Daniel Sobral-Blanco, Camille Bonvin

One of the main goal of large-scale structure surveys is to test the consistency of General Relativity at cosmological scales. In the $\Lambda$CDM model of cosmology, the relations between the fields describing the geometry and the content of our Universe are uniquely determined. In particular, the two gravitational potentials -- that describe the spatial and temporal fluctuations in the geometry -- are equal. Whereas large classes of dark energy models preserve this equality, theories of modified gravity generally create a difference between the potentials, known as anisotropic stress. Even though measuring this anisotropic stress is one of the key goals of large-scale structure surveys, there are currently no methods able to measure it directly. Current methods all rely on measurements of galaxy peculiar velocities (through redshift-space distortions), from which the time component of the metric is inferred, assuming that dark matter follows geodesics. If this is not the case, all the proposed tests fail to measure the anisotropic stress. In this letter, we propose a novel test which directly measures anisotropic stress, without relying on any assumption about the unknown dark matter. Our method uses relativistic effects in the galaxy number counts to provide a direct measurement of the time component of the metric. By comparing this with lensing observations our test provides a direct measurement of the anisotropic stress.

Johannes U. Lange, Andrew P. Hearin, Alexie Leauthaud, Frank C. van den Bosch, Hong Guo, Joseph DeRose

We use a simulation-based modelling approach to analyse the anisotropic clustering of the BOSS LOWZ sample over the radial range $0.4 \, h^{-1} \, \mathrm{Mpc}$ to $63 \, h^{-1} \, \mathrm{Mpc}$, significantly extending what is possible with a purely analytic modelling framework. Our full-scale analysis yields constraints on the growth of structure that are a factor of two more stringent than any other study on large scales at similar redshifts. We infer $f \sigma_8 = 0.471 \pm 0.024$ at $z \approx 0.25$, and $f \sigma_8 = 0.431 \pm 0.025$ at $z \approx 0.40$; the corresponding $\Lambda$CDM predictions of the Planck CMB analysis are $0.470 \pm 0.006$ and $0.476 \pm 0.005$, respectively. Our results are thus consistent with Planck, but also follow the trend seen in previous low-redshift measurements of $f \sigma_8$ falling slightly below the $\Lambda$CDM+CMB prediction. We find that small and large radial scales yield mutually consistent values of $f \sigma_8$, but there are $1-2.5 \sigma$ hints of small scales ($< 10 \, h^{-1} \, \mathrm{Mpc}$) preferring lower values for $f \sigma_8$ relative to larger scales. We analyse the constraining power of the full range of radial scales, finding that most of the multipole information about $f\sigma_8$ is contained in the scales $2 \, h^{-1} \, \mathrm{Mpc} \lesssim s \lesssim 20 \, h^{-1} \, \mathrm{Mpc}$. Evidently, once the cosmological information of the quasi-to-nonlinear regime has been harvested, large-scale modes contain only modest additional information about structure growth. Finally, we compare predictions for the galaxy-galaxy lensing amplitude of the two samples against measurements from SDSS and assess the lensing-is-low effect in light of our findings.

Eanna E Flanagan

When a black hole first forms, the properties of the emitted radiation as measured by observers near future null infinity are very close to the 1974 prediction of Hawking. However, deviations grow with time, and become of order unity after a time $t \sim M_i^{7/3}$, where $M_i$ is the initial mass in Planck units. After an evaporation time the corrections are large: the angular distribution of the emitted radiation is no longer dominated by low multipoles, with an exponential fall off at high multipoles. Instead, the radiation is redistributed as a power law spectrum over a broad range of angular scales, all the way down to the scale $\Delta \theta \sim 1/M_i$, beyond which there is exponential falloff. This effect is is a quantum gravitational effect, whose origin is the spreading of the wavefunction of the black hole's center of mass location caused by the kicks of the individual outgoing quanta, discovered by Page in 1980. The modified angular distribution of the Hawking radiation has an important consequence: the number of soft hair modes that can effectively interact with outgoing Hawking quanta increases from the handful of modes at low multipoles $l$, to a large number of modes, of order $\sim M_i^2$. We argue that this change unlocks the Hawking-Perry-Strominger mechanism for solving the information loss paradox.