Dark Matter & BAO: How Does it Suppress Baryonic Oscillations?

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Discussion Overview

The discussion centers on the role of dark matter in suppressing baryonic oscillations, particularly in the context of the cosmic microwave background (CMB) power spectrum and structure formation in the early universe. Participants explore theoretical implications and the interaction between dark matter and baryonic matter.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that dark matter density significantly affects the CMB power spectrum and structure formation, suggesting that a substantial amount of dark matter is necessary to reconcile observed structures with those predicted by baryonic matter alone.
  • Others argue that dark matter does not suppress baryonic oscillations but rather does not participate in them due to its lack of pressure response, contributing to odd peaks in the CMB power spectrum while normal matter contributes to even peaks.
  • A later reply questions whether dark matter suppresses even peaks by acting gravitationally against baryonic matter, affecting its expansion.
  • One participant references a video by Sean Carroll to explain the gravitational effects of dark matter on baryonic oscillations.
  • Another participant raises a hypothetical scenario regarding the mass of electrons and its potential impact on charge separation in the primordial plasma, suggesting it could mimic the effects of dark matter.
  • A subsequent response challenges the validity of the mass claim about electrons, emphasizing the invariance of rest mass and requesting clarification on the statement.

Areas of Agreement / Disagreement

Participants express differing views on whether dark matter suppresses baryonic oscillations or merely does not participate in them. The discussion remains unresolved with multiple competing perspectives presented.

Contextual Notes

Some claims depend on specific interpretations of the CMB power spectrum and the role of dark matter, which may not be universally accepted. The discussion includes speculative scenarios that introduce additional complexity.

wolram
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How does dark matter suppress baryonic osculations?
 
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The dark matter density in the early universe has a significant effect on the peaks in the CMB power spectrum, which strongly affects structure formation in the early universe, e.g., SDSS [see; https://arxiv.org/abs/1509.06529, SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 12: galaxy target selection and large scale structure catalogues. You need a pretty healthy dose of DM to reconcile the observed structure with that expected based solely on baryonic matter and radiation pressure in the early universe [DM is not affected by radiation pressure]. For discussion, see http://background.uchicago.edu/~whu/intermediate/driving2.html. It is difficult to appreciate the strength of the case for DM without familiarity with CMB and SDSS studies.
 
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wolram said:
How does dark matter suppress baryonic osculations?
I don't think it suppresses them. It just doesn't participate in them (as dark matter doesn't experience pressure to any significant degree). In practical terms this means that dark matter contributes to all of the odd peaks in the CMB power spectrum, while only the normal matter contributes to the even peaks.
 
Chalnoth said:
I don't think it suppresses them. It just doesn't participate in them (as dark matter doesn't experience pressure to any significant degree). In practical terms this means that dark matter contributes to all of the odd peaks in the CMB power spectrum, while only the normal matter contributes to the even peaks.
But it does, doesn't it? - it suppresses the even peaks as it acts gravitationally against the bouncing baryonic matter so that it doesn't expand as much as a result.
This animation from Max Tegmark's site:
http://space.mit.edu/home/tegmark/movies.html
shows the effect each cosmological parameter should have on peak distribution.

@wolram Sean Carroll briefly explains how this works in this video:

starting at around 15:40 (or, -9.45).
 
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If, in the primordial plasma, electrons were 2000x less massive than ions, wouldn't a given photon flux have had much greater effect on the motion of electrons over ions ? Wouldn't that create a charge separation which would suppress even peaks, mimicking non-baryonic DM in so doing ?
 
The mass of the electron doesn't change. Rest mass being an invarient quantity. If you have a different invarient mass it's not a electron. So where did you get this value ?

Edit your wording is extremely ambiguous can you clarify the above ?
 

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