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### CAMB: modifying diffusion physics

Posted: May 26 2019
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.

### Re: CAMB: modifying diffusion physics

Posted: May 26 2019
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.

### Re: CAMB: modifying diffusion physics

Posted: May 27 2019
Ah OK, I didn't appreciate that was an approximation. Thanks. I guess that means there's no way to modify diffusion physics without also modifying e.g. timing of recombination.