CAMB: equations_PPF.f90 question

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Per Andersen
Posts: 3
Joined: November 17 2015
Affiliation: University of Copenhagen

CAMB: equations_PPF.f90 question

Post by Per Andersen » December 03 2015

Hi,

I'm working on a project where I need to modify the parameterisation w(a) = w0 + wa * (1-a) from the equations_PPF.f90 file used in CAMB and CosmoMC.

I can tell that I definitely need to modify line 98:

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w_de=w_lam+wa_ppf*(1._dl-a)
But then in line 143 we have:

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grho_de=grhov*a**(1._dl-3.*w_lam-3.*wa_ppf)*exp(-3.*wa_ppf*(1._dl-a))
I'm unsure exactly what this equation is. To me it looks very close to the behaviour of dark energy density which is:

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f(a) = a**(-3.*(1+w_lam+wa_ppf)) * exp(-3*wa_ppf*(1.-a))
(See e.g. Appendix A of King 2014, http://arxiv.org/abs/1311.2356)

So, in summary - what role does line 143 of equations_PPF.f90 play in CAMB, and if I want to modify the w(a) = w0 + wa * (1-a) parameterisation do I also need to modify line 143 and not just line 98?

Thank you!
- Per

Antony Lewis
Posts: 1636
Joined: September 23 2004
Affiliation: University of Sussex
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Re: CAMB: equations_PPF.f90 question

Post by Antony Lewis » December 03 2015

Yes. grho_de(a) returns [tex]8 \pi G a^4\rho_{de}[/tex].

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