The trouble with H {sub 0}
- ICC, University of Barcelona, IEEC-UB, Martí i Franquès, 1, E08028 Barcelona (Spain)
We perform a comprehensive cosmological study of the H {sub 0} tension between the direct local measurement and the model-dependent value inferred from the Cosmic Microwave Background. With the recent measurement of H {sub 0} this tension has raised to more than 3 σ. We consider changes in the early time physics without modifying the late time cosmology. We also reconstruct the late time expansion history in a model independent way with minimal assumptions using distance measurements from Baryon Acoustic Oscillations and Type Ia Supernovae, finding that at z < 0.6 the recovered shape of the expansion history is less than 5% different than that of a standard ΛCDM model. These probes also provide a model insensitive constraint on the low-redshift standard ruler, measuring directly the combination r {sub s} h where H {sub 0} = h × 100 Mpc{sup −1}km/s and r {sub s} is the sound horizon at radiation drag (the standard ruler), traditionally constrained by CMB observations. Thus r {sub s} and H {sub 0} provide absolute scales for distance measurements (anchors) at opposite ends of the observable Universe. We calibrate the cosmic distance ladder and obtain a model-independent determination of the standard ruler for acoustic scale, r {sub s}. The tension in H {sub 0} reflects a mismatch between our determination of r {sub s} and its standard, CMB-inferred value. Without including high-ℓ Planck CMB polarization data (i.e., only considering the ''recommended baseline' low-ℓ polarisation and temperature and the high ℓ temperature data), a modification of the early-time physics to include a component of dark radiation with an effective number of species around 0.4 would reconcile the CMB-inferred constraints, and the local H {sub 0} and standard ruler determinations. The inclusion of the ''preliminary' high-ℓ Planck CMB polarisation data disfavours this solution.
- OSTI ID:
- 22679435
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2016, Issue 10; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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