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waynehu

Professor, Department of Astronomy and Astrophysics
University of Chicago

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PPF module for CAMB

Wenjuan Fang

The main CAMB code supports smooth dark energy models with constant equation of state and sound speed of one, or a quintessence model based on a potential (code). This modified code generalizes it to support a time-dependent equation of state w(a) that is allowed to cross the phantom divide, i.e. w=-1 multiple times by implementing a Parameterized Post-Friedmann(PPF) prescription for the dark energy perturbations (see references below).

Download here

The modifications are based on the latest CAMB version of September 2008. Three files are modified, i.e. equations.f90, inidriver.F90, and params.ini, and the modified code supports two options to specify w(a),

Then to use the code, you only need to rename the modified files as the original ones, or modify the Makefile to use the alternative f90 files, and all remaining procedures are the same as you do with the original CAMB.

Note, the outputted matter power spectra may have up to 10% difference from direct calculations of scalar field dark energy models when k is approaching 10-4 h/Mpc, but accurate to a level of better than 0.2% once k is smaller than 10-3 h/Mpc.

References

W. Hu & I. Sawicki, A Parameterized Post-Friedmann Framework for Modified Gravity, Phys. Rev. D 76:104043 (2007), arXiv:0708.1190.
W. Hu, Parametrized Post-Friedmann Signatures of Acceleration in the CMB, Phys. Rev. D 77:103524 (2008). arXiv:0801.2433.
W. Fang et al., Challenges to the DGP Model from Horizon-Scale Growth and Geometry, Phys. Rev. D 78:103509 (2008). arXiv:0808.2208.
W. Fang, W. Hu & A. Lewis, Crossing the Phantom Divide with Parameterized Post-Friedmann Dark Energy, Phys. Rev. D 78:087303(2008).arXiv:0808.3125.