Cosmic Variance and the Measurement of the Local Hubble Parameter
Abstract
There is an approximately 9% discrepancy, corresponding to 2.4σ, between two independent constraints on the expansion rate of the Universe: one indirectly arising from the cosmic microwave background and baryon acoustic oscillations and one more directly obtained from local measurements of the relation between redshifts and distances to sources. We argue that by taking into account the local gravitational potential at the position of the observer this tension—strengthened by the recent Planck results—is partially relieved and the concordance of the Standard Model of cosmology increased. We estimate that measurements of the local Hubble constant are subject to a cosmic variance of about 2.4% (limiting the local sample to redshifts z>0.010) or 1.3% (limiting it to z>0.023), a more significant correction than that taken into account already. Nonetheless, we show that one would need a very rare fluctuation to fully explain the offset in the Hubble rates. If this tension is further strengthened, a cosmology beyond the Standard Model may prove necessary.
 Publication:

Physical Review Letters
 Pub Date:
 June 2013
 DOI:
 10.1103/PhysRevLett.110.241305
 arXiv:
 arXiv:1303.3121
 Bibcode:
 2013PhRvL.110x1305M
 Keywords:

 98.80.Es;
 98.62.Py;
 98.65.Dx;
 98.70.Vc;
 Observational cosmology;
 Distances redshifts radial velocities;
 spatial distribution of galaxies;
 Superclusters;
 largescale structure of the Universe;
 Background radiations;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 5 pages, 4 figures. v2: added one figure, improved results and discussion, added references. v3: updated to Planck results. v4: matches version accepted for publication in PRL