# I Dark matter and Antimatter

1. Feb 16, 2017

### rootone

Observations have led to the conclusion that the Universe contains dark matter,
a form of matter that has mass and therefore gravity, but apparently doesn't interact otherwise with 'normal' matter.
It's existence is unexplained.
Then there is the puzzle of antimatter, a form of baryonic normal matter with charges reversed.
The Universe has basically no antimatter, although insignificant quantities can be produced by nuclear reactions.
The big bang should have produced equal amounts of matter and antimatter but it didn't;
there was enough of an excess of normal matter so that stars and galaxies could form eventually.
It's tempting to draw the conclusion that the presence of dark matter and the absence of antimatter are related.
I am sure i am not the first to be tempted by that idea.
What relevant research does anyone know of.
This is not a personal theory by the way, I will be very happy to be told that there cannot possibly be any connection.

2. Feb 16, 2017

### Staff: Mentor

I don't see any reason to draw this conclusion. The two are very different.

I'm under the impression that observations of dark matter require that it be completely different from antimatter, in which case no research would be done since the two have already been shown to be different.

3. Feb 16, 2017

### phinds

Yeah, what he said.

Dammit, rootone, you've got me agreeing w/ Drakkith. I hate doing that.

4. Feb 16, 2017

### Orodruin

Staff Emeritus
That they have different properties does not mean there is no connection. In fact, the similar abundances (factor of five in density) have given popularity to models of asymmetric dark matter, which loosely are theories where an asymmetry between DM and anti-DM and not thermal freezeout is responsible for the dark matter abundance. Many of those models provide a link between the baryon and dark matter asymmetries (and thus abundances). I have some papers on this subject.

Some of these theories produce an asymmetry in one sector which is then shared with the other sector through effective processes or sphalerons. Others imply that dark matter carries an effective baryon number and the total baryon number (in the visible and dark sectors combined) is equal to zero.

Not saying that antimatter is dark matter (clearly ruled out), but I find it misleading to claim that their abundances cannot have anything to do with each other.

5. Feb 16, 2017

### rootone

No question that they are completely different.
My reasoning was that any form of matter consists of an arrangement of subatomic particles, quarks, and possibly beneath that, strings.
Our current model can't explain why there should be any dark matter, neither can it explain shortage of antimatter.
So the thought occurs that while these are very different things, they both are an arrangement of more fundamental particles.
In the early universe could one arrangement transform to another/
Similarly to ice and water being very different, but are still made of fundamentally the same stuff.

6. Feb 16, 2017

### Staff: Mentor

Well, it appears I've inserted my foot into my mouth. I'll just bow out here while I still have a leg (and foot) to stand on.

7. Feb 16, 2017

Staff Emeritus
Reminds me of "This isn't homework". Of course it's a personal theory.

8. Feb 16, 2017

### rootone

I have no idea how they could be related and no evidence that they are, so am not challenging anything.
Ever had an experience like opening the fridge to take out a pizza that you know is there, but when you look it isn't, but there is a different pizza. An unsolvable dilemma
Anyway done with this now, I have got the message that counting apples in units of oranges is futile.

Hyman's Categorical Imperative:
Do not try to explain something until you are sure there is something to be explained.

Last edited: Feb 16, 2017
9. Feb 16, 2017

### Staff: Mentor

Eh, I don't consider this a personal theory. Just a question asking if there is any relationship between dark matter and antimatter. As Orodruin said, there are papers on this subject.

And Orodruin has us both eating our boots. I hope yours taste better than mine.

10. Feb 17, 2017

Staff Emeritus
Well,

Is a statement, not a question. Message #5 is a defense of that statement.

Furthermore, I would argue that "We don't know the reason for X" and "We do not know the reason for Y" does not lead to the conclusion that X and Y are related. Or that they are unrelated.

11. Feb 17, 2017

### maroubrabeach

I'm not sure that is really correct....Is its existence anymore unexplained then normal baryonic matter?

Obviously we had an excess of matter over anti matter, otherwise we would not be here.
Why is another question.
Also its worth thinking about that if we were made of anti matter, instead of normal matter, then we would be calling normal matter, anti matter, and anti matter, normal matter, if you know what I mean.
Some thoughts on the subject in the following paper........................
https://arxiv.org/pdf/1512.08482.pdf

Is a symmetric matter-antimatter universe excluded?

ABSTRACT

We consider a non-standard cosmological model in which the universe contains as much matter as antimatter on large scales and presents a local baryon asymmetry. A key ingredient in our approach is that the baryon density distribution follows Gaussian fluctuations around a null value η = 0. Spatial domains featuring a positive (resp. negative) baryonic density value constitute regions dominated by matter (resp. antimatter). At the domains’ annihilation interface, the typical density is going smoothly to zero, rather than following an abrupt step as assumed in previous symetric matter-antimatter models. As a consequence, the Cosmic Diffuse Gamma Background produced by annihilation is drastically reduced, allowing to easily pass COMPTEL’s measurements limits. Similarly the Compton y distorsion and CMB “ribbons” are lowered by an appreciable factor. Therefore this model essentially escape previous constrainst on symetric matter-antimatter models. However, we produce an estimation of the CMB temperature fluctuations that would result from this model and confront it to data acquired from the Planck satellite. We construct a angular power spectrum in δT/TCMB assuming is can be approximated as an average of C over a Gaussian distribution of ΩB using Lewis & Challinor’s CAMB software. The resulting C are qualitatively satisfying. We quantify the goodness of fit using a simple χ 2 test. We consider two distinct scenarios in which the fluctuations on ΩB are compensated by fluctuations on ΩCDM to assure a spatially flat Ωκ = 0 universe or not. In both cases, out best fit have ∆χ 2 & 2400 (with respect to a fiducial ΛCDM model), empirically excluding our model by several tens of standard deviations

12. Feb 17, 2017

### Staff: Mentor

I find that questions are often cloaked as statements, as people commonly combine the question and the reason for asking the question together. This does not make it a personal theory. In any case, this is off topic for the thread, so please feel free to contact me or make a thread in the mentor's forums if you'd like to discuss this further.