Directional dependence of the local estimation of $H_0$ and the non perturbative effects of primordial curvature perturbations

Abstract

Recent measurements of the cosmic microwave background (CMB) radiation have shown an apparent tension with the present value of the Hubble parameter inferred from local observations of supernovae, which look closer, i.e. brighter, than what is expected in a homogeneous model with a value of $H_0$ equal to the one estimated from CMB observations. We examine the possibility that such a discrepancy is the consequence of the presence of a local inhomogeneity seeded by primordial curvature perturbations, finding that a negative peak of the order of less than two standard deviations could allow to fit low red-shift supernovae observations without the need of using a value of the Hubble parameter different from $H_0^{CMB}$. The type of inhomogeneity we consider does not modify the distance to the last scattering, making it compatible with the constraints of the PLANCK mission data. Our calculation is fully relativistic and non perturbative, and for this reason shows important effects which were missed in the previous investigations using relativistic perturbations or Newtonian approximations, because the structures seeded by primordial curvature perturbations can be today highly non linear, and relativist Doppler terms cannot be neglected. Comparison with studies of local structure based on galaxy surveys and luminosity density analysis reveals that the density profile we find could in fact be compatible with the one obtained for the same region of sky where is located most of the Cepheids used to calibrate the luminosity distance of the supernovae employed for the local $H_0$ estimation, suggesting a possible directional dependence and calibration bias which could be partially attributed to the presence of the Sloan Great Wall.