What is the difference between FRW and LCDM models

Post Reply
Noble P Abraham
Posts: 9
Joined: July 31 2008
Affiliation: School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam

What is the difference between FRW and LCDM models

Post by Noble P Abraham » March 05 2010

Please help me, what is the difference between the following [tex] d_L [/tex] relations

1. FRW model
[tex]d_L=5 \mbox{log} \left( (1+z) \frac{c}{H_0} |\Omega_k|^{-1/2}\ \mbox{Sinn} \left[ \ |\Omega_k|^{1/2} \int _{0}^{z} [(1+z^{\prime })^{2}(1+\Omega_{m}z^{\prime})-z^{\prime}(2+z^{\prime} )(\Omega _{\Lambda})]^{-1/2}\; dz^{\prime} \right] \right)[/tex]
where
[tex]\Omega_k=1-\Omega_m-\Omega_\Lambda[/tex]
[tex]\mbox{Sinn}(x) = \mbox{Sin}(x) \mbox{ for } \Omega_m + \Omega_\Lambda > 1 [/tex]
[tex]\mbox{Sinn}(x) = \mbox{Sinh}(x) \mbox{ for } \Omega_m + \Omega_\Lambda < 0 [/tex]
and
[tex]\mbox{Sinn}(x) = x \mbox{ for } \Omega_m + \Omega_\Lambda = 1 [/tex]
(From Moncy & Narlikar, astro-ph/0111122, Drell et. al., astro-ph/9905027)

2. [tex]\Lambda[/tex]CDM model
[tex]d_L=5 \mbox{log} \left( (1+z) \frac{c}{H_0} |\Omega_k|^{-1/2}\ \mbox{Sinn} \left[ \ |\Omega_k|^{1/2} \int _{0}^{z} [\Omega_m (1+z^{\prime }) ^3+\Omega_k (1+z^{\prime })^2+\Omega_\Lambda]^{-1/2}\; dz^{\prime} \right] \right)[/tex]

where
[tex]\Omega_k=\frac{k}{H_0 ^2}[/tex]
[tex]\mbox{Sinn}(x) = \mbox{Sin}(x) \mbox{ for } k > 0 [/tex]
[tex]\mbox{Sinn}(x) = \mbox{Sinh}(x) \mbox{ for } k< 0 [/tex]
and
[tex]\mbox{Sinn}(x) = x \mbox{ for } k = 0 [/tex]

(From Szydlowski and Godlowski, astro-ph/0509415)

Can I put [tex]\Omega_k=1-\Omega_m-\Omega_\Lambda[/tex] in the second case ([tex]\Lambda[/tex]CDM) as well?

Kindly treat me as a beginner and correct me.

Ben Gold
Posts: 81
Joined: September 25 2004
Affiliation: University of Minnesota
Contact:

What is the difference between FRW and LCDM models

Post by Ben Gold » March 06 2010

Can I put &#937;k = 1 &#8722; &#937;m &#8722; &#937;&#923; in the second case (&#923;CDM) as well?
Yes, if you do that and perform some algebra you should find that they're exactly the same equation.

Post Reply