CosmoCoffee

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.

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%.