The Dyer-Roeder distance-redshift relation in inhomogeneous universes

Using Monte-Carlo methods, we determine the best-fit value of the homogeneity parameter alpha in the Dyer-Roeder distance-redshift relation for a variety of redshifts, inhomogeneity models and cosmological parameter values. The relation between alpha and the fraction of compact objects, f_p, is found to be approximately linear. This relation can be parametrized with reasonable accuracy for all cases treated in this paper by alpha = a*f_p, where a = 0.6.Comment: 5 pages, 10 figures, submitted to Phys.Rev.

Impact of symmetron screening on the Hubble tension: new constraints using cosmic distance ladder data

Fifth forces are ubiquitous in modified theories of gravity. To be compatible with observations, such a force must be screened on solar-system scales but may still give a significant contribution on galactic scales. If this is the case, the fifth force can influence the calibration of the cosmic distance ladder, hence changing the inferred value of the Hubble constant $H_0$. In this paper, we analyze symmetron screening and show that it generally increases the Hubble tension. On the other hand, by doing a full statistical analysis, we show that cosmic distance ladder data are able to constrain the theory to a level competitive with solar-system tests -- currently the most constraining tests of the theory. For the standard coupling case, the constraint on the symmetron Compton wavelength is $\lambda_{\rm C} \lesssim 2.5 \, \mathrm{Mpc}$. Thus, distance ladder data constitutes a novel and powerful way of testing this, and similar, types of theories.Comment: 11 pages, 9 figures. Comments are welcom

Probing a scale dependent gravitational slip with galaxy strong lensing systems

Observations of galaxy-scale strong gravitational lensing systems enable unique tests of departures from general relativity at the kpc-Mpc scale. In this work, the gravitational slip parameter $\gamma_{\rm PN}$, measuring the amplitude of a hypothetical fifth force, is constrained using 130 elliptical galaxy lens systems. We implement a lens model with a power-law total mass density and a deprojected De Vaucouleurs luminosity density, favored over a power-law luminosity density. To break the degeneracy between the lens velocity anisotropy, $\beta$, and the gravitational slip, we introduce a new prior on the velocity anisotropy based on recent dynamical data. For a constant gravitational slip, we find $\gamma_{\rm PN}=0.90^{+0.18}_{-0.14}$ in agreement with general relativity at the 68\% confidence level. Introducing a Compton wavelength $\lambda_g$, effectively screening the fifth force at small and large scales, the best fit is obtained for $\lambda_g \sim 0.2$ Mpc and $\gamma_{\rm PN} = 0.77^{+0.25}_{-0.14}$. A local minimum is found at $\lambda_g \sim 100$ Mpc and $\gamma_{\rm PN}=0.56^{0.45}_{-0.35}$. We conclude that there is no evidence in the data for a significant departure from general relativity and that using accurate assumptions and having good constraints on the lens galaxy model is key to ensure reliable constraints on the gravitational slip.Comment: 12 pages, 5 figure