Interacting models in CAMB

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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David Figuer
Posts: 2
Joined: September 16 2019
Affiliation: University of Salamanca

Interacting models in CAMB

Post by David Figuer » September 16 2019

Hello everyone,

I am new on CAMB and I want to implement some modifications on the perturbations equations due to a dark energy-dark matter interaction. The kind of modifications I want is easy but I have several questions.
I only want to change the dark energy and dark matter velocity equations using the synchronous gauge:

a) In the model I have, it is not allowed to use the residual gauge freedom to set v_c=0 even it is the synchronous gauge, therefore, should I create a new set of equations and variables in the equations.f90 module to implement a v_c differential equations?

b) In the dark energy sector, should I just modify the DarkEnergyFluid.f90 by adding a term with the Dark matter velocity v_c?

c) If so, how I make CAMB to understand that both equations dark energy and dark matter (delta_c, theta_c, delta_de and theta_de) are all coupled?

d) If I want to use the python camb, should I modify the files I need in \CAMB\fortran and then use "python setup.py make
" and finally use a .ini file in the command line?

Thanks in advance and sorry if it seems as easy questions or asked before but I am totally new on CAMB.

Antony Lewis
Posts: 1522
Joined: September 23 2004
Affiliation: University of Sussex
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Re: Interacting models in CAMB

Post by Antony Lewis » September 16 2019

Yes, you would have to modify the equations for the relevant perturbation variables and add an additional equation for v_c. You'll need to modify the fortran code and build it as you say. You'd probably also want to propagate your new parameters to the python interface unless you only want to use from the command line (in which case you can just run the "make" and use the fortran binary).

David Figuer
Posts: 2
Joined: September 16 2019
Affiliation: University of Salamanca

Re: Interacting models in CAMB

Post by David Figuer » September 17 2019

Hello, first of all thanks for the reply!

Just a detail, in order to make CAMB to understand the perturbation equations for dark matter and dark energy are coupled what I should do? Put all the equations in the same subroutine or there is anything pre-done in CAMB that can be used?

Thank you!

Sunny Vagnozzi
Posts: 51
Joined: August 15 2016
Affiliation: Kavli Institute for Cosmology (KICC), University of Cambridge

Re: Interacting models in CAMB

Post by Sunny Vagnozzi » September 17 2019

Along a similar line, I'm also wondering, would one need to set basic_num_eqns=5 (instead of the default 4) in fortran/equations.f90, since you now have an equation for v_c instead of v_c=0 as in the "usual" synchronous gauge?

Antony Lewis
Posts: 1522
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: Interacting models in CAMB

Post by Antony Lewis » September 18 2019

Yes, you'd have to edit equations.f90, increasing basic_num_eqns and adding relevant additional equations and terms where needed.

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