The trouble with H₀

Abstract

Abstract. We perform a comprehensive cosmological study of the H 0 tension between the direct local measurement and the model-dependent value inferred from the Cosmic Microwave Background. With the recent measurement of H 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 s h where H 0 = h × 100 Mpc −1 km/s and r s is the sound horizon at radiation drag (the standard ruler), traditionally constrained by CMB observations. Thus r s and H 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 s . The tension in H 0 reflects a mismatch between our determination of r s and its standard, CMB-inferred value. Without including high-Planck CMB polarization data (i.e., only considering the "recommended baseline" low-polarisation and temperature and the high 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 0 and standard ruler determinations. The inclusion of the "preliminary" high-Planck CMB polarisation data disfavours this solution.arXiv:1607.05617v2 [astro-ph.CO]

SU(2)CMB at high redshifts and the value of H0

“…Subsequently, we compute rs(z lf, * ) and rs(z lf,drag ). With the rs − H0 relation of Bernal, Verde & Riess (2016) we deduce from our value of rs(z lf,drag ) a good match of H0 with the value given in Riess et al (2016). In Sec.…”

“…Fortunately, our high-z cosmological model, which is conservative concerning its (solely baryonic) matter content and the number of massless neutrino flavours but invokes SU(2)CMB to describe the CMB itself, can be tested in terms of the most basic low-z cosmological parameter: today's value of the cosmic expansion rate H0. This test relies on an inverse proportionality between the co-moving sound horizon at baryon freezeout rs and H0 which was extracted from low-z data (Cepheid calibrated SNe Ia, new parallax measurements, stronger constraints on the Hubble flow, and a refined computation of distance to NGC4258 from maser data) under no model assumptions other than spatial flatness, SNe Ia/rs yielding standard candles/a standard ruler, and a smooth expansion history Bernal, Verde & Riess (2016). Obviously, this knowledge is important because it allows a high-z extraction of rs to determine H0.…”

Determining the Hubble Constant From Hubble Parameter Measurements

“…Although one of the most measured cosmological parameters, it was more than seven decades after Hubble's first measurement before a consensus value for H 0 started to emerge. In Freedman et al (2001 (Aubourg et al 2015; also see Ross et al 2015;Bernal et al 2016;L'Huillier & Shafieloo 2016;Luković et al 2016), with the Planck 2015 CMB data value being =  H 67.8 0 -0.9 km s 1 Mpc −1 (Ade et al 2015; but see Addison et al 2016).…”

Interacting dark sector and precision cosmology

“…Were these discrepancies to be of physical origin (rather than unaccounted-for systematics), they would be a sign of the need for new physics beyond ΛCDM, and that a new cosmological model ought to take its place. Different studies on these discrepancies have appeared in the literature ( [10][11][12][13][14][15][16][17][18][19][20][21]). …”