Speaker
Description
The late-time Universe features nonlinear local deviations from strict homogeneity and isotropy as matter structures develop. These inhomogeneities may have a non-negligible impact on the cosmological expansion at the largest scales. Such "backreaction" effects from the presence of structures, including the growth of spatial curvature over large regions, can partially mimic the dynamical contributions of dark energy or dark matter depending on the scale considered. They can be described, in a general-relativistic picture, by explicitly coarse-graining the local inhomogeneous fields using a spatial averaging scheme.
We evaluate the local density, expansion rate, shear, and spatial intrinsic scalar curvature fields within a 300 Mpc/h comoving distance of our Galaxy (z ~ 0.1) using the CosmicFlows-4++ reconstruction of the associated peculiar velocity and density contrast fields. This allows us to compute the averaged energy balance over a range of scales in the cosmic neighbourhood, including the contributions from backreaction terms.
I will present these results, which show large (O(10%)) regional deviations in the energy budget from the flat $\Lambda$CDM background, with a significant role played by the spatial curvature. These variations extend all the way to the edge of the surveyed volume, where they point to a vast underdense shell roughly compatible with the proposed Local Hole.
| Research Area | Cosmology: late universe |
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