Amplitude of velocity perturbations at last scattering

In summary, the conversation discusses the need for a precise estimate of the magnitude of velocity perturbations at the time of last scattering as a function of multipole moment. The temperature power spectrum of CMB suggests that the peculiar velocities were around dv/c ~ 10^-5, but a more accurate calculation is needed due to the small contribution of the Doppler effect. The speaker also asks for any references for numerical values of dv for different multipole moments. They suggest using linear perturbation theory to determine gravitational potentials and compute average velocities.
  • #1
smallphi
441
2
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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  • #2
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.
 

Related to Amplitude of velocity perturbations at last scattering

1. What is the amplitude of velocity perturbations at last scattering?

The amplitude of velocity perturbations at last scattering refers to the magnitude of the fluctuations in the velocity of matter in the early universe, which were imprinted onto the cosmic microwave background (CMB) radiation. This amplitude is typically measured in units of microns per second (μm/s) and is an important indicator of the density and structure of the universe at that time.

2. How is the amplitude of velocity perturbations at last scattering determined?

The amplitude of velocity perturbations at last scattering is determined through observations of the CMB radiation. Scientists use telescopes and satellites to measure the temperature fluctuations in the CMB, which are directly related to the velocity perturbations. By analyzing these fluctuations, scientists can calculate the amplitude of the velocity perturbations at last scattering.

3. What does the amplitude of velocity perturbations at last scattering tell us about the early universe?

The amplitude of velocity perturbations at last scattering provides important information about the density and distribution of matter in the early universe. This can give us insights into the processes that shaped the universe and led to the formation of galaxies and other cosmic structures. It also helps us understand the overall geometry and evolution of the universe.

4. How does the amplitude of velocity perturbations at last scattering affect the CMB power spectrum?

The amplitude of velocity perturbations at last scattering is one of the main factors that affects the CMB power spectrum. The power spectrum is a plot of the intensity of CMB radiation at different wavelengths. The amplitude of velocity perturbations influences the shape and amplitude of the power spectrum, providing valuable information about the universe's composition and evolution.

5. Can the amplitude of velocity perturbations at last scattering change over time?

Yes, the amplitude of velocity perturbations at last scattering can change over time. In fact, it is expected to change as the universe evolves and matter and energy interact with each other. Scientists study the changes in the amplitude of velocity perturbations over time to gain a better understanding of the dynamics of the early universe and the forces shaping its evolution.

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