Abstract
We demonstrate that the instabilities in linear cosmological perturbations in bimetric theory are the manifestation of the non-linear Vainshtein mechanism on an FRW background. The spin-2 mass serves as the cosmological Vainshtein scale in this case. This allows us to quantitatively address early universe cosmology. In particular, in a global analysis, we study data from the cosmic microwave background radiation and local measurements of the Hubble flow. We show that bimetric cosmology resolves the discrepancy in the local and early-time measurements of the Hubble scale via an effective phantom dark energy component.
Highlights
Modifications and extensions to the theory of general relativity (GR) are highly restricted [1,2]
We demonstrate that the early Universe in bimetric theory is screened by the Vainshtein mechanism on a Friedmann-Lemaître-Robertson-Walker background
We show that bimetric cosmology resolves the discrepancy in the local and early-time measurements of the Hubble scale via an effective phantom dark energy component
Summary
Modifications and extensions to the theory of general relativity (GR) are highly restricted [1,2]. In static systems with spherical symmetry an analogous behavior occurs [7,36,37,38,39]: Nonlinear effects in the perturbations are relevant and render the linear approximation invalid This is the well-known Vainshtein screening mechanism [7] that restores GR in spacetime regions where the energy density is large (compared to the spin-2 mass). As discussed in the literature [42,43,44,45,46,47,48,49,50,51,52,53,54,55], cosmic microwave background (CMB) observations tend to predict a lower Hubble scale than local measurements We demonstrate that this tension can be resolved in a minimal realization of bimetric theory with only two more parameters than the ΛCDM model. We comment on the compatibility between the different observables and argue that the ΛCDM and the β0β1β4 models are distinguishable with future measurements
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