Amplitude of velocity perturbations at last scattering

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SUMMARY

The discussion focuses 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 temperature fluctuations of dT/T ~ 10^-5, suggesting that peculiar velocities are approximately dv/c ~ 10^-5. However, a more precise estimate is required, as the Doppler effect contributes minimally to dT/T in the CMB. The discussion recommends using gravitational potentials derived from the temperature fluctuations and applying the virial theorem to compute average velocities, necessitating knowledge of linear perturbation theory.

PREREQUISITES
  • Understanding of Cosmic Microwave Background (CMB) temperature power spectrum
  • Familiarity with peculiar velocities in cosmology
  • Knowledge of linear perturbation theory
  • Application of the virial theorem in astrophysics
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  • Research the derivation of peculiar velocities from CMB temperature fluctuations
  • Study the application of linear perturbation theory in cosmology
  • Explore the virial theorem and its implications in astrophysical contexts
  • Investigate numerical methods for calculating multipole moments in CMB analysis
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Astronomers, cosmologists, and astrophysicists interested in the analysis of Cosmic Microwave Background fluctuations and the dynamics of the early universe.

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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