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[1003.2185] Confirmation of general relativity on large sca

Posted: March 11 2010
by Beth Reid
The authors introduce a new statistic which eliminates both galaxy bias and sigma8 through the combination of galaxy-galaxy clustering, galaxy-galaxy lensing, and a measurement of redshift space distortions from anisotropic galaxy clustering. The authors present new measurements of the first two, and rely on Tegmark et al. (2006) for a measurement of [tex]\beta[/tex] from redshift space distortions.

It can be used as a test of GR (and to constrain models of modified gravity). The statistic is

[tex]E_G = \frac{1}{\beta} \frac{\Gamma_{gm}(R)}{\Gamma_{gg}(R)}[/tex]

which in GR+[tex]\Lambda[/tex]CDM is [tex]\Omega_{m,o}/f(z) = 0.408 \pm 0.029[/tex].

Their measurements are in agreement with [tex]N[/tex]-body + HOD mock LRG catalogs, indicating that the measurement is robust to non-linearities.

They compare to the predictions of f(R) and TeVeS, which predict substantially different values than GR+[tex]\Lambda[/tex]CDM. While the errors are still quite large, this should prove to be an extremely valuable statistic in the near future.

[1003.2185] Confirmation of general relativity on large sca

Posted: March 11 2010
by Neal Dalal
Yes, this paper looks very interesting! Are they basically measuring the equality of the two metric potentials [tex]\Phi[/tex] and [tex]\Psi[/tex], assuming linear bias?

How should I interpret the [tex]f(R)[/tex] prediction? Presumably, outside the Compton wavelength gravity matches GR, and inside the Compton wavelength gravity is 4/3 stronger, so is their result an upper bound on the Compton wavelength? Or does the Chameleon mechanism become important on the scales of interest, [tex]\sim[/tex]20 Mpc? Or am I thinking about this wrong?

It's also neat that their measurement constrains Omega_m pretty well, to about 15%.