Evolution of the fσ8 Tension with the Planck15-ΛCDM Determination and Implications for Modified Gravity Theories.
This is the repository that contains the Mathematica code (in .zip format) as well as useful comments that reproduce the figures of 10.1103/PhysRevD.97.103503 which can also be found in arxiv:1803.01337.
We construct an updated extended compilation of distinct (but possibly correlated) fσ8(z) redshift space distortion (RSD) data published between 2006 and 2018. It consists of 63 data points and is significantly larger than previously used similar data sets. After fiducial model correction we obtain the best fit Ω0m-σ8 ΛCDM parameters and show that they are at a 5σ tension with the corresponding Planck15-ΛCDM values. Introducing a nontrivial covariance matrix correlating randomly 20% of the RSD data points has no significant effect on the above tension level. We show that the tension disappears (becomes less than 1σ) when a subsample of the 20 most recently published data is used. A partial cause for this reduced tension is the fact that more recent data tend to probe higher redshifts (with higher errorbars) where there is degeneracy among different models due to matter domination. Allowing for a nontrivial evolution of the effective Newton's constant as
(gα is a parameter) and fixing a Planck15-ΛCDM background we find gα=-0.91± 0.17 from the full fσ8 data set while the 20 earliest and 20 latest data points imply and
respectively. Thus, the more recent fσ8 data appear to favor general relativity in contrast to earlier data. Finally, we show that the parametrization
provides an excellent fit to the solution of the growth equation for both general relativity (gα=0) and modified gravity (gα≠0).
If you use any of the above codes or the figures in a published work please cite the following paper:
Evolution of the fσ8 Tension with the Planck15-ΛCDM Determination and Implications for Modified Gravity Theories.
Lavrentios Kazantzidis, Leandros Perivolaropoulos
Phys.Rev. D97 (2018) no.10, 103503, arxiv:1803.01337.
Any further questions/comments are welcome.
Lavrentios Kazantzidis - [email protected]
Leandros Perivolaropoulos - [email protected]