Amplitude of velocity perturbations at last scattering

AI Thread Summary
The discussion centers on determining the magnitude of peculiar velocity perturbations (dv) at the time of last scattering, specifically as a function of multipole moments. The temperature power spectrum of the Cosmic Microwave Background (CMB) indicates fluctuations of dT/T ~ 10^-5, suggesting dv/c ~ 10^-5, but a more precise estimate is sought due to the small contribution of the Doppler effect. Participants suggest calculating gravitational potentials from the temperature fluctuations and using the virial theorem to derive average velocities, which requires knowledge of linear perturbation theory. The need for numerical references for dv at different multipole moments is emphasized. Accurate quantification of these peculiar velocities is crucial for understanding the CMB's temperature fluctuations.
smallphi
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I need to know the magnitude of the velocity perturbations (peculiar velocities) dv at time of last scattering as function of the multipole moment.

The temperature power spectrum of CMB shows temperature fluctuations dT/T ~ 10^-5. That naively suggests the peculiar velocities were dv/c ~ 10^-5. I need more precise estimate than that since the Dopler effect is a small contribution to the dT/T in CMB.

Any reference where dv are derived and shown numerically for different multipole moments?
I need numbers like dv/c = 10^-5 or 10^-4 etc.
 
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smallphi said:
I need to know the magnitude of the velocity perturbations (peculiar velocities) dv at time of last scattering as function of the multipole moment.

The temperature power spectrum of CMB shows temperature fluctuations dT/T ~ 10^-5. That naively suggests the peculiar velocities were dv/c ~ 10^-5. I need more precise estimate than that since the Dopler effect is a small contribution to the dT/T in CMB.

Any reference where dv are derived and shown numerically for different multipole moments?
I need numbers like dv/c = 10^-5 or 10^-4 etc.
Well, I can't give you an answer straight away, but it seems to me that a good way to go about this would be to first determine the gravitational potentials that result from having dT/T ~ 10^-5, and then compute the average velocities using the virial theorem. Going this route would requite some knowledge of linear perturbation theory.
 
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