Speaker
Description
The late Universe features nonlinear deviations from strict homogeneity and isotropy as matter structures develop. These local inhomogeneities may have a non-negligible dynamical impact on the cosmological expansion. Such backreaction effects from the presence of structures also include the growth of spatial curvature over large regions. They can be described in a general-relativistic picture, by explicitly coarse-graining the local inhomogeneous fields using a spatial averaging scheme.
I will present our estimates of the contributions to the averaged energy budget, including the relativistic backreaction effects, over a range of scales around our Galaxy, up to a 300 Mpc/h comoving distance (z ~ 0.1). We used the CosmicFlows-4++ reconstruction of the peculiar velocity and density contrast fields within this range, and a mapping between Newtonian and GR frameworks, to evaluate the corresponding local density, expansion rate, shear, and scalar intrinsic spatial curvature fields.
I will discuss the significant (O(10%)) regional deviations that we observe with respect to the imposed flat $\Lambda$CDM background, which extend all the way to the edge of the surveyed volume. The scale-dependent variations in all averaged fields point to a vast underdense shell roughly compatible with the proposed Local Hole, surrounding further nested wall and void structures at a more local level. I will highlight in particular the important role played by spatial curvature in the obtained regional energy balance and in its variations with the averaging scale.