Is there a concordance value for H₀?

¹ Dipartimento di Fisica, Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
e-mail: vladimir.lukovic@roma2.infn.it
² Sezione INFN, Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy

Received: 29 January 2016
Accepted: 20 July 2016

Abstract

Context. We test the theoretical predictions of several cosmological models against different observables to compare the indirect estimates of the current expansion rate of the Universe determined from model fitting with the direct measurements based on Cepheids data published recently.

Aims. We perform a statistical analysis of type Ia supernova (SN Ia), Hubble parameter, and baryon acoustic oscillation data. A joint analysis of these datasets allows us to better constrain cosmological parameters, but also to break the degeneracy that appears in the distance modulus definition between H₀ and the absolute B-band magnitude of SN Ia, M₀.

Methods. From the theoretical side, we considered spatially flat and curvature-free ΛCDM, wCDM, and inhomogeneous Lemaître-Tolman-Bondi (LTB) models. To analyse SN Ia we took into account the distributions of SN Ia intrinsic parameters.

Results. For the ΛCDM model we find that Ω_m = 0.35 ± 0.02, H₀ = (67.8 ± 1.0) km s^-1 Mpc^-1, while the corrected SN absolute magnitude has a normal distribution N(19.13,0.11). The wCDM model provides the same value for Ω_m, while H₀ = (66.5 ± 1.8) km s^-1 Mpc^-1 and w = −0.93 ± 0.07. When an inhomogeneous LTB model is considered, the combined fit provides H₀ = (64.2 ± 1.9) km s^-1 Mpc^-1.

Conclusions. Both the Akaike information criterion and the Bayes factor analysis cannot clearly distinguish between ΛCDM and wCDM cosmologies, while they clearly disfavour the LTB model. For the ΛCDM, our joint analysis of the SN Ia, the Hubble parameter, and the baryon acoustic oscillation datasets provides H₀ values that are consistent with cosmic microwave background (CMB)-only Planck measurements, but they differ by 2.5σ from the value based on Cepheids data.