Fluctuations Flashcards
What is the result of the Transfer equation for wavelengths greater than Jean’s length?
1 and less than 1 for smaller wavelengths
What is the transfer equation?
It encapsulates the way different wavelengths grow
What is δ_initial(k)?
The initial fluctuation spectrum
What is δ_f (k,z = 0)?
The final value from fluctuation for a given value of k at z = 0
What is D(z)?
How much a k value which is always greater than Jean’s length grows
Which fluctuations always grow at horizon wavelength squared?
Those outside of horizon as they are always larger than Jean’s length
What happens to fluctuations which enter horizon before matter radiation equality?
They stop growing
What happens to fluctuations after matter-radiation equality?
Cold dark matter fluctuations start growing again and become proportional to horizon wavelength squared
What happens between the matter-radiation equality and recombination?
Baryonic fluctuations only grow on scales larger than the horizon size
When do baryons experience damped oscillations?
between recomb and matter radiation equality on scales less than horizon size
What happens to fluctuations after recombination?
Everything apart from radiation grows until 1 + z ~ 1/Ω_0 -1
What happens to baryons after recombination?
Baryons fall into dark matter potential wells so experience the same growth as the dark matter by today
What does the CMB contain info about?
baryon fluctuations as they were at recombination
How are baryon fluctuations seen in the CMB?
By removing the global constant temperature and the effect due to our motion (Doppler shift)
What is adiabatic coupling?
The fluctuation in the total energy is shared between all of the different particles by equipartition
