CosmoCoffee

Hi,

I am working with CAMB-1.0.12, and I am trying to modify some physics. My first aim is to artificially suppress the growth of only the small scale (large wavenumber k) density perturbations of the cold dark matter species.

I tried to modify the “equation of motion” for the CDM in the “equations.f90” file, which normally reads:
Clxdot=-k*z

I then recompiled using “python setup.py make”, but when I run the simulation, I see no difference in the result, even when replacing the above equation with Clxdot=-k*z*0.

My questions are:
1) I should see some effect of a modified equation of motion, so what am I doing wrong? Am I modifying the wrong equation, or in the wrong file? Is there a problem with recompiling?

2) In “equations.f90” I found the baryon equation of motion: clxbdot=-k*(z+vb). But this equation seems different than what I expected from e.g. Eq. 5-30 in arXiv:astro-ph/9804301v2. Also “dz” seems different than expected from Eq. 5-31. I have looked around but didn’t find exactly the underlying theory behind “equations.f90”. Am I missing something here?

3) Is there a simple intuitive argument why the evolution of perturbations of one species (e.g. Delta_baryon) is independent of the choice of Omega_bh^2 or Omega_cdm^2? From Eq. 6-22 in in arXiv:astro-ph/9804301v2 I would expect that the evolution of each species depends on the SUM of all densities and pressures of all other species.

All feedback is much appreciated,
Filip

Sounds OK, make sure you re-start Python. The equations neglect some very small pressure terms (matter pressure is only important when coupled via derivatives so the last term in 5-30 is very small).

The evolution equations are not independent of those quantities (except in some limits).

Hi,

I have now managed to change the equations of motion in the file "equations.f90", to compile and run - so far so good...

But I still have trouble locating the following equations found in ScalEqs.txt in the file "equations.f90":

drhob:=-3*H(t)*(rhob(t)+pb(t))
drhoc:=-3*H(t)*rhoc(t);

Can somebody point out exactly in which line of equations.f90 these calculations (namely the effect of expansion on the densities of each species) are carried out?

Thanks a lot,

Filip

How did you do to compile before running? Is it enough to do "make" inside the fortran folder?

"python setup.py make" in the main folder will update an existing "pip install -e" installation.