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Showing votes from 2017-07-04 11:30 to 2017-07-07 12:30 | Next meeting is Tuesday May 12th, 10:30 am.
This paper shows that emerging spatial curvature is a generic feature of relativistic inhomogeneous models of the large-scale universe. This phenomenon is absent in the Standard Cosmological Model, which has a flat and fixed spatial curvature (small perturbations are considered in the Standard Cosmological Model but their global average vanishes, leading to spatial flatness at all times). This paper shows that with the nonlinear growth of cosmic structures the global average deviates from zero. The analysis is based on the {\em silent universes} (a wide class of inhomogeneous cosmological solutions of the Einstein equations) interwoven into the Styrofoam-type configuration. The initial conditions are set in the early universe as perturbations around the $\Lambda$CDM model with $\Omega_m = 0.31$, $\Omega_\Lambda = 0.69$, and $H_0 = 67.8$ km s$^{-1}$ Mpc$^{-1}$. As the growth of structures becomes nonlinear, the model deviates from the $\Lambda$CDM model, and at the present instant if averaged over a domain with mass $M = 3.2 \times 10^{20} M_{\odot}$ and volume $V = (2150\,{\rm Mpc})^3$ (at these scales the cosmic variance is negligibly small) gives: $\Omega_m^{\cal D} = 0.22$, $\Omega_\Lambda^{\cal D} = 0.61$, $\Omega_{\cal R}^{\cal D} = 0.15$ (in the FLRW limit $\Omega_{\cal R}^{\cal D} \to \Omega_k$), and $\langle H \rangle_{\cal D} = 72.2$ km s$^{-1}$ Mpc$^{-1}$. Given the fact that low-redshift observations favor higher values of the Hubble constant and lower values of matter density, compared to the CMB constraints, the emergence of the spatial curvature in the low-redshift universe could be an obvious solution to these discrepancies.
Pure massive gravity is strongly coupled at a certain low scale, known as Lambda_3. I show that the theory can be embedded into another one, with new light degrees of freedom, to increase the strong scale to a significantly larger value. Certain universal aspects of the proposed mechanism are discussed, notably that the coupling of the longitudinal mode to a stress-tensor is suppressed, thus making the linear theory consistent with the fifth-force exclusion. An example of the embedding theory studied in detail is 5D AdS massive gravity, with a large cosmological constant. In this example the 4D strong scale can be increased by 19 orders of magnitude. Holographic duality then suggests that the strong scale of the 4D massive gravity can be increased by coupling it to a 4D non-local CFT, endowed with a UV cutoff; however, the 5D classical gravity picture appears to be more tractable.