via Dr H: will we ever find DM?

[notFritzArgelander]

https://time.com/5744094/find-dark-matt ... DRfSCC7H5A

Reasonable article from a former fan of WIMPs.

To be fair, Dr H's POV is: "This article is notable for not even mentioning the possibility that dark matter is not a particle." Dr H has been holding out for alternative gravity theories that have been falsified, though.

The only "non particle" explanations I like are massive topological defects in spacetime. Other particles such as axions and Kaluza-Klein particles have not been adequately explored.

Next project will be to update the scorecard on performance of alternative gravity theories I had at the other place.

[Michael131313]

Thanks n_FA. Waiting for your updated scorecard on performance of alternative gravity theories. Enjoyed them.

[pakarinen]

IIRC, she was / is advocating some kind of superfluid? I just skimmed it, so the details never registered.

[AntennaGuy]

IIRC, she was / is advocating some kind of superfluid? I just skimmed it, so the details never registered.

That's a different Dr. H. You're thinking Hossenfelder. nFA linked to Hooper. (I was initially confused, too.)

[metastable]

I've been wondering whether the down quark could be a composite particle. Suppose it consisted of 3 electrons and 4 up quarks, this would have the same charge as a down quark. Also in the case of a free neutron decay, if the 3 electrons and 4 up quarks split up into the up quark (which remains to form the proton), the electron (beta particle), and another composite of 2 electron and 3 up quarks, this would have 0 charge. Could a 5 particle composite of 2 electrons and 3 up quarks be the neutrino and dark matter?

[AntennaGuy]

I've been wondering whether the down quark could be a composite particle. Suppose it consisted of 3 electrons and 4 up quarks, this would have the same charge as a down quark. Also in the case of a free neutron decay, if the 3 electrons and 4 up quarks split up into the up quark (which remains to form the proton), the electron (beta particle), and another composite of 2 electron and 3 up quarks, this would have 0 charge. Could a 5 particle composite of 2 electrons and 3 up quarks be the neutrino and dark matter?

It's been too long since I studied particle physics, but I strongly suspect your speculations are inconsistent with established QED/QCD physics and experimental confirmations thereof. But if not, then this could get interesting...

[helicon]

Thanks for posting this article notFritz - highly interesting and there are future research ramifications.

[notFritzArgelander]

IIRC, she was / is advocating some kind of superfluid? I just skimmed it, so the details never registered.

She's been pushing the limp noodle of Verlinde's emergent gravity, which is a relativistic version of MOND.

[notFritzArgelander]

IIRC, she was / is advocating some kind of superfluid? I just skimmed it, so the details never registered.

That's a different Dr. H. You're thinking Hossenfelder. nFA linked to Hooper. (I was initially confused, too.)

Sorry. I quoted Sabine Hossenfelder's (Dr H) criticism of Hooper's article. You can get ok galaxy rotation curves only for galaxies with "the average" dark matter content. For different DM abundances Verlinde's theory and MOND fail. Hooper knows this but Hossenfelder's not acknowledged it yet.

For anything else (Big Bang nucleosynthesis, large structure and galaxy formation) MOND and Verlinde's are useless.

[notFritzArgelander]

I've been wondering whether the down quark could be a composite particle. Suppose it consisted of 3 electrons and 4 up quarks, this would have the same charge as a down quark. Also in the case of a free neutron decay, if the 3 electrons and 4 up quarks split up into the up quark (which remains to form the proton), the electron (beta particle), and another composite of 2 electron and 3 up quarks, this would have 0 charge. Could a 5 particle composite of 2 electrons and 3 up quarks be the neutrino and dark matter?

The electron does not interact via the strong interaction so the size of a down quark structure you propose would be fixed by the electromagnetic interaction alone. It would be on the order of a hydrogen atom's size. This is contradicted by deep inelastic scattering results that show that down quarks are smaller than the proton.

[metastable]

If they’re initially close enough could gravity become significant?

[notFritzArgelander]

If they’re initially close enough could gravity become significant?

There are two answers depending on how close they are. The distance at which the answers differ is the Planck length.

https://en.m.wikipedia.org/wiki/Planck_length

1) For separations larger than the Planck length the answer is definitely no. The reason is that for such separations we know that gravitation is extremely weak compared to electromagnetism. Comparing the dimensionless fine structure constants of the two forces shows this.

https://en.m.wikipedia.org/wiki/Gravita ... g_constant
https://en.m.wikipedia.org/wiki/Fine-structure_constant

2) For smaller than Planck length separations the answer is that there is no answer. A quantum gravity theory would be required and we don't have a clear winner there.

However any hypothesis that the down quark is a composite particle would have to make a prediction that differs from the Standard Model and is confirmed experimentally.

[notFritzArgelander]

If they’re initially close enough could gravity become significant?

There are two answers depending on how close they are. The distance at which the answers differ is the Planck length.

https://en.m.wikipedia.org/wiki/Planck_length

1) For separations larger than the Planck length the answer is definitely no. The reason is that for such separations we know that gravitation is extremely weak compared to electromagnetism. Comparing the dimensionless fine structure constants of the two forces shows this.

https://en.m.wikipedia.org/wiki/Gravita ... g_constant
https://en.m.wikipedia.org/wiki/Fine-structure_constant

2) For smaller than Planck length separations the answer is that there is no answer. A quantum gravity theory would be required and we don't have a clear winner there.

However any hypothesis that the down quark is a composite particle would have to make a prediction that differs from the Standard Model and is confirmed experimentally.

The above was a purely theoretical answer. The experimental situation is that deep inelastic scattering first revealed that quarks were point like entities within hadrons, not mere mathematical conveniences. This was established in the 1960s and 1970s so, old hat.

https://en.wikipedia.org/wiki/Deep_inelastic_scattering

The experimental situation has not changed much. https://en.wikipedia.org/wiki/Quark#Size

In QCD, quarks are considered to be point-like entities, with zero size. As of 2014, experimental evidence indicates they are no bigger than 10^−4 times the size of a proton, i.e. less than 10^−19 metres.

[metastable]

Suppose it consisted of 3 electrons and 4 up quarks, this would have the same charge as a down quark. Also in the case of a free neutron decay, if the 3 electrons and 4 up quarks split up into the up quark (which remains to form the proton), the electron (beta particle), and another composite of 2 electron and 3 up quarks, this would have 0 charge. Could a 5 particle composite of 2 electrons and 3 up quarks be the neutrino and dark matter?

Is there any way this could be tested? It seems like at least a mildly significant coincidence that 3 electrons and 4 up quarks have the same charge as a down quark, and dividing them in the manner described gives the same composite charges as the free neutron decay products as well...

[notFritzArgelander]

Suppose it consisted of 3 electrons and 4 up quarks, this would have the same charge as a down quark. Also in the case of a free neutron decay, if the 3 electrons and 4 up quarks split up into the up quark (which remains to form the proton), the electron (beta particle), and another composite of 2 electron and 3 up quarks, this would have 0 charge. Could a 5 particle composite of 2 electrons and 3 up quarks be the neutrino and dark matter?

Is there any way this could be tested? It seems like at least a mildly significant coincidence that 3 electrons and 4 up quarks have the same charge as a down quark, and dividing them in the manner described gives the same composite charges as the free neutron decay products as well...

Is there any chance that one could get funding for such a test? No. It already fails consistency tests with known physics. For the reasons given above it's physical nonsense. Physics tests require physics ideas not numerological coincidences.

Your idea is DOA, dead on arrival, since it is incompatible with experiments already done.

[metastable]

Well I know that under ordinary circumstances color confinement forbids it, but not necessarily in quark gluon plasma--

"Since the energy scale of inflation and the Planck scale are relatively close, some of the quantum fluctuations that have made up the structure in our universe were smaller than the Planck length before inflation. Therefore, there ought to be corrections from Planck-scale physics, in particular the unknown quantum theory of gravity."

https://en.wikipedia.org/wiki/Inflation_(cosmology)

You had said that there is no answer if they are closer than the planck length... but I thought during inflation the whole universe was smaller than the planck length and at temperatures necessary for quark gluon plasma. The prediction would be that neutrinos are heavier than thought unless the binding energy negates some of that mass discrepency.

[notFritzArgelander]

Well I know that under ordinary circumstances color confinement forbids it, but not necessarily in quark gluon plasma--

FALSE! Contradicted by deep inelastic scattering results since the 1960s-1970s AND experiments on quark gluon plasmas done at SPS and LHC at CERN, and at RHIC. All these use point quarks. A composite quark would give different results.

A person competent to think about the idea of the down quark being composite would have the ability to self criticize and discard the idea as already incoherent with what is known.

"Since the energy scale of inflation and the Planck scale are relatively close, some of the quantum fluctuations that have made up the structure in our universe were smaller than the Planck length before inflation. Therefore, there ought to be corrections from Planck-scale physics, in particular the unknown quantum theory of gravity."

https://en.wikipedia.org/wiki/Inflation_(cosmology)

You had said that there is no answer if they are closer than the planck length... but I thought during inflation the whole universe was smaller than the planck length and at temperatures necessary for quark gluon plasma.

FALSE! The whole universe is infinite and flat always even while the observable universe gets close to being Planck length small.

The prediction would be that neutrinos are heavier than thought unless the binding energy negates some of that mass discrepency.

What prediction? You have no prediction. You only have an appeal to quantum gravity as though it were Harry Potter's magic wand.

[metastable]

I'm willing to dismiss the idea while noting the QGPs done at the SPS, LHC and RHIC didn't reach the same temperatures and densities as inflation QGP.

[notFritzArgelander]

I'm willing to dismiss the idea while noting the QGPs done at the SPS, LHC and RHIC didn't reach the same temperatures and densities as inflation QGP.

More magical thinking. Why do you think that the composite nature of the down quark would reveal itself at higher energies? What binds your proposal so tightly that it looks point like at all available energies? You need a new magical force field. What's your proposal?

Is it another Yang-Mills field? What is its gauge symmetry?

So far it looks more like Hogwarts Academy than the Institute for Advanced Study.

[metastable]

I previously said gravity

If they’re initially close enough could gravity become significant?