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Why is the CMB power spectrum often plotted as l(l+1) C_l and not only C_L ?

  1. May 17, 2012 #1
    Hello everybody, (sorry for the eventual Engrish)

    I can't find any convincing answer for the following question :

    Why do we always (or often) plot the CMB power spectrum in this way :
    jb.man.ac.uk/research/cosmos/vsa/images/CMB_power_spectrum.gif

    I mean the y axis is $$C_\ell \ell (\ell+1)$$ and not only $$C_\ell. $$ Why ?

    Thanks for your answer. I already heard that its because of we want show the plateau at low l. But if it is the answer, why is the plateau proportional to $$\ell (\ell +1) ?$$

    Thanks :)
     
  2. jcsd
  3. May 17, 2012 #2

    George Jones

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    From http://relativity.livingreviews.org/open?pubNo=lrr-1998-11&page=articlesu14.html [Broken]
    If a log scale is used for [itex]\ell[/itex], scale invariance is a flat line. Scale invariance is expected at large angular scales (low [itex]\ell[/itex]), hence the plateau.
     
    Last edited by a moderator: May 6, 2017
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