# W and gamma

(*Nick writing on behalf of Mat*)

From the sigma8(z) constraints posted (sigma 8 of z constraints link), we looked into how well we can constrain w and delta gamma, where delta gamma quantifies a departure from the GR growth rate gamma (see Weinberg et al. 2012).

Temperature plus polarization CMB Halo mass calibration. The error bands are for z-bins of width 0.1

Polarization only CMB Halo mass calibration

gamma = 0.55 + 0.05(1 + w) and Delta gamma equivalent to 0.05(1 + w) so w = -0.8 corresponds to delta gamma 0.01.

Note that a lot of the constraint for w (and mnu) is just coming from pinning down sigma8 today. Not so much from knowing its z dependence. Although if there were some motivation for a general w(z) or delta gamma (z), those would be better constrained by this.