CosmoCoffee

Posted: **January 30 2020**

Hi all,

I am trying to modify the equation file for quintessence for CAMB provided at https://camb.info/equations_quint.f90.
In subroutine EvolveBackground, the energy density of the scalar field is defined as

Code: Select all

tmp=a2*(0.5d0*phidot**2 + a2*Vofphi(phi,0))

which is consistent with the standard definition

\rho_{\phi}=\dfrac{\phi'^2}{2 a^2} + V(\phi) (eq. 6.5 in Theory of cosmological perturbations ) upto a overall factor of

a^4 where prime denotes the derivative with respect to the conformal time.
But later in the file in function Quint_GetOmegaFromInitial, it is given that

Code: Select all

Quint_GetOmegaFromInitial=(0.5d0*y(2)**2 + Vofphi(y(1),0))/(3*adot**2)

which is supposed to produce the value of

\Omega_{\phi}, which should be

\rho_{\phi} multiplied by an overall factor.
But considering the definition

Code: Select all

y(2)=phidot*astart**2

this doesn't seem to be consistent with the definition

Code: Select all

tmp=a2*(0.5d0*phidot**2 + a2*Vofphi(phi,0))

since

Code: Select all

(0.5d0*y(2)**2 + Vofphi(y(1),0))

is equivalent to

\dfrac{\phi'^2}{2} astart^4+ V(\phi) which cannot be same as the definition of $\rho_{\phi}$ or $\Omega_{\phi}$ irrespective of any overall factor.

I am not sure if it is an error in the code, or if I am missing something.

Best
Joseph

Posted: **January 30 2020**

Omega is only calculated at a=1?

Posted: **March 02 2020**

Thanks for the reply. I had not noticed that Omega was calculated at a=1.

CosmoCoffee

Equations in Quint module in quintessence equations file for CAMB

Equations in Quint module in quintessence equations file for CAMB

Re: Equations in Quint module in quintessence equations file for CAMB

Re: Equations in Quint module in quintessence equations file for CAMB