Tension between local and CMB measurements of Hubble constant

[mitchell porter]

"A 2.4% Determination of the Local Value of the Hubble Constant" by Riess et al has led to some excited news stories recently. I don't see it discussed anywhere here. Looking for the essence of the paper, I note three things:

1. The two measurements considered are "the Hubble constant ... measured locally" and "the sound horizon observed from the cosmic microwave background radiation"
2. Possible causes of a discrepancy include "time-dependent or early dark energy, gravitational physics beyond General Relativity, additional relativistic particles, or nonzero curvature"
3. "Systematic uncertainties in CMB measurements may [also] play a role in the tension"

 

[phyzguy]

We discussed this last week in my research group. This is not a new problem, but the newer, more accurate measurement by Riess et.al. has made the discrepancy worse. The consensus among the people I talked to is that it is hard to see how the local measurement can be wrong by the amount required to make it consistent with Planck. On question I had that I don't know the answer to is whether sterile neutrinos as hypothesized in the Nu-MSM model can help. I think the answer is no, since these neutrinos are massive and not relativistic, but I'm not certain. Anybody?

 

[Chronos]

The Riess data only considers the value of H_0 out to z=0.15. I wonder how the value of H_0 looks over different redshift bins. If the value of H_0 trends according to redshift range this finding would be more interesting, IMO. Right now, it looks like a case of unknown systematic errors. Obviously, local [z<0.15] redshift measures should be more accurate simply because our distance measures are more accurate at z<0.15 than we can realistically expect at higher z values.