CAMB: Modifying the Code to Define an Arbitrary w(a)

[Dror Berechya]

Hello everyone,

I have modified the `set_params()` function in `cosmo_packages/code/CAMB/camb/` to define a new dark energy model where the equation of state is described by calling `self.set_w_a_table(a, w)` to effectively represent an arbitrary function for [math]w(a).

I have two questions regarding my modification:

• Is this modification sufficient to describe a new dark energy model that affects only the background dynamics?

• Is it possible to make this model dependent on sampled parameters that are not traditionally included in an equation for [math]w(a), such as [math]\Omega_m h^2? If so, should I do this by including the relevant parameter in the `set_params()` input parameters, or do I need to specify it in other parts of the code?

Thank you very much for your help,
Dror

[Antony Lewis]

It can't by default depend on cosmological parameters, but you could probably modify the call in camb.set_params to pass additional info. The dependencies can get a bit complicated in general (e.g. if you set thetastar and a dark energy model, some parameters like H0/Omega_m will change depending on the dark energy model at fixed omch2).