## CAMB: modifying diffusion physics

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Posts: 27
Joined: July 17 2014
Affiliation: Johns Hopkins University

### CAMB: modifying diffusion physics

Is it possible to edit camb/equations.f90 to change the physics of diffusion damping when computing the CMB power spectra, e.g. modify the photon mean free path? My understanding was that the impact of the diffusion damping for some particular k-mode was captured in a multiplicative function that in principle could be separated from other physical effects, but I'm having trouble figuring out from the code whether this is the case.

Antony Lewis
Posts: 1484
Joined: September 23 2004
Affiliation: University of Sussex
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### Re: CAMB: modifying diffusion physics

You'd have to modify the scattering terms for the Boltzmann equation, e.g. most simply by changing the Thomson scattering cross-section. The D(k) is only an approximation and is not used.