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Directional dependence of the local estimation of H0 and the nonperturbative effects of primordial curvature perturbations

10 June 2015

Time: 4:30pm
Venue: G. O. Jones 516
The London Relativity and Cosmology Seminar
Antonio Enea Romano (Kyoto)

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 H0 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 HCMB0. 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. The effect on the luminosity
distance is in fact localized around the region in space where the
transition between different values of the curvature perturbations
occurs, producing a local decrease, while the distance outside the
inhomogeneity is not affected. Comparison with studies of local
structure based on galaxy surveys analysis reveals that the density
profile we find could in fact be compatible with the one obtained for
the same region of sky where most of the supernovae used for the local
H0 estimation are located, suggesting a possible directional dependence
which could be partially attributed to the presence of the Sloan Great
Wall and hinting to the need of a more careful investigation, including 

a wider set of low redshift supernovae in different regions of the sky

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