Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

F(R) gravity and the Hubble parameter

  1. Feb 12, 2016 #1
    Dear all,

    Considering Einstein Hilbert lagrangian, by using Einstein field equations one can get the form of Friedman equations and consequently the Hubble parameter.
    I know that in f(R) models, Einstein equations get modified. However, what happens to the Friedman equation and the Hubble parameter?
    I tried to solve them and get to the form of H, but it seems such a complicated equation.

    Using the (00) component, I get
    H^2=\frac{8\pi G}{3}\rho -\frac{6\alpha}{c^2}(\frac{\ddot{a}^2}{a^2} + H^4)
    What should I do with the
    \begin{equation} \ddot{a}^2\end{equation}
    in the first equation?!!
    The (11) component just makes everything more complicated!!
    I really appreciate any help or idea.
    BTW, I am using FRW metric.
    Last edited: Feb 12, 2016
  2. jcsd
  3. Feb 12, 2016 #2
    I just realized that the equations consist the forth order of the scale factor (a(t)).
    Are these solvable in the matter dominated era? when
    \rho(z)=\rho_m a^{-3}
  4. Feb 15, 2016 #3
    Has anybody seen any paper on the change of hubble parameter with f(R)? Is there at least any approximation?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook