# Dark Matter - spin=?

1. Jan 12, 2010

### Dmitry67

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 dont interact with themselves.

2. Jan 12, 2010

Staff Emeritus
DM clouds are far, far, far too diffuse for Pauli blocking to have an effect.

3. Jan 12, 2010

### Dmitry67

1. So we cant 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?

4. Jan 12, 2010

Staff Emeritus
No, you can't make a WIMP arbitrarily light. Then you have hot dark matter, and we know dark matter is cold.

5. Jan 13, 2010

### Prologue

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?

6. Jan 13, 2010

### Dmitry67

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 dont know neither temperature nor mass alone

7. Jan 13, 2010

Staff Emeritus
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.

8. Jan 13, 2010

### twofish-quant

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.

9. Jan 13, 2010

### Dmitry67

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?