Dark Matter Spin: Is WIMP DM Different?

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Discussion Overview

The discussion revolves around the implications of dark matter (DM) spin, specifically focusing on Weakly Interacting Massive Particles (WIMPs) and whether different spins (1/2 or 1) lead to distinct testable predictions. Participants explore theoretical aspects, observational constraints, and the relationship between particle properties and large-scale structure in the universe.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that if DM is matter with spin=1/2, the Pauli principle could lead to degenerate DM clouds, potentially creating additional pressure despite WIMPs' self-interaction limitations.
  • Others argue that DM clouds are too diffuse for Pauli blocking to have a significant effect.
  • There is a question about whether it is possible to distinguish WIMPs with spin=1/2 from those with spin=1 based on current theoretical frameworks.
  • Some participants assert that WIMPs cannot be arbitrarily light, as this would classify them as hot dark matter, which contradicts the cold dark matter model.
  • One participant challenges the logic regarding the relationship between particle mass, velocity, and temperature, seeking clarification on how these factors are interrelated.
  • Another participant suggests that if WIMPs were very light, they would have high velocities that could prevent them from forming large-scale structures in the universe.
  • Concerns are raised about the observational limits on the velocity of WIMPs and how these limits relate to the temperature and mass of the particles.
  • There is a discussion about the implications of light WIMPs on large-scale structure formation, with some suggesting that if WIMPs were light enough to allow for Pauli exclusion effects, they would also have velocities that could disrupt structure formation.

Areas of Agreement / Disagreement

Participants express multiple competing views on the implications of WIMP spin and mass on dark matter properties and structure formation. The discussion remains unresolved with no consensus on the key questions raised.

Contextual Notes

Participants note limitations in defining the temperature and mass of WIMPs, as well as the dependence of particle concentration on the effects of degeneration. There are unresolved mathematical steps regarding the relationships between temperature, mass, and velocity.

Dmitry67
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Are there any different testable predictions of the DM (WIMPs) having different spin: 1/2 or 1?

For example, if DM is *matter* (spin=1/2) then Pauli princliple can make dense DM cloulds 'degenerate', creating an additional pressure, even WIMPs don't interact with themselves.
 
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DM clouds are far, far, far too diffuse for Pauli blocking to have an effect.
 
1. So we can't tell WIMPs with spin=1/2 from WIMPs with spin=1?
2. Too diffuse? Degeneration depends on the concentration of particles (N of particles per volume), not density. No matter how they are diffuse WIMPs can be light enough so degeneration takes place. What are the current lower and upper limits for the rest mass of a single WIMP particle?
 
No, you can't make a WIMP arbitrarily light. Then you have hot dark matter, and we know dark matter is cold.
 
Vanadium 50 said:
No, you can't make a WIMP arbitrarily light. Then you have hot dark matter, and we know dark matter is cold.

I don't follow this line of logic. For the same energy you would have higher velocities, but still it is at the same energy, so the same temperature. What factors are you taking into consideration when you state that the temperature would be higher just because of a lower mass per particle?
 
He probably meant 'if WIPMs were very light they will be moving too fast and they would escape from the galaxies'

This is correct, but it means that the DM we know upper limits of VELOCITY. If we assume that WIPMs have some particular mass, we get the temperture. If we define the temperature, we get the lower limit for the mass.

But we don't know neither temperature nor mass alone
 
Well, actually what I meant was that you don't get the large scale structure right. But whatever. The point is that uber-light WIMPS are not consistent with observation.
 
Dmitry67 said:
2. Too diffuse? Degeneration depends on the concentration of particles (N of particles per volume), not density. No matter how they are diffuse WIMPs can be light enough so degeneration takes place. What are the current lower and upper limits for the rest mass of a single WIMP particle?

I don't recall off hand what the limits are for the mass of a WIMP, but I do recall that if they were light enough so that Pauli exclusion were to have an impact, then they would be light enough to have high enough velocities to smear out large scale structure. If WIMP's were light and high temperature, then the it would be like throwing an snowflake in boiling water. You wouldn't get any large scale structure at all.
 
So the observational data put some limits on v<vmax
As T is proportional to mv^2, we have upper bound for T/m
Are there any other upper/lower limits for T and m?
 

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