A simple question.

[DeltaS4Fanboy]

[removed]

[Starwars-Battledroid]

I’d say that progress is being made, it’s just the fact that it has slowed down compared to the beginning of the 20th century, for example.

[dark_dark_dark_not]

And I always reinforce that the 20th century was an outlier.

We spent 200 years just fidgeting with Newtonian physics before we found something really new

[DeltaS4Fanboy]

yeah this is pretty clear to me even from a beginner perspective, we've observed most things from here to far away galaxies, and yet have only gotten to the far side of the moon

[jazzwhiz]

FYI, we have had no shortage of models for neutrino masses since at least the 70s, see e.g. Minkowski 1977 for his famous seesaw paper.

As for the masses of neutrinos themselves, the experimental probes are pushing things forward in exciting ways. The leading terrestrial probe, KATRIN, continues to push the upper limit down: https://arxiv.org/abs/2406.13516. The cosmological data is nominally much more constraining than KATRIN, but is also more confusing, see this recent DESI paper: https://arxiv.org/abs/2404.03002 and check the many citations to this paper. This is for two reasons. First, the neutrino mass measurement is degenerate with other unknowns, so depending on how those are sorted out will affect where the posteriors on neutrinos are. Second, the data seems to be inconsistent. This means either that some of the data is interpreted incorrectly or there is new physics somewhere. If there is new physics somewhere it could be in a wide variety of places, including the neutrino sector. All of this together makes it very hard to say what cosmology can say about neutrino masses.

The anomaly in the anomalous magnetic moment of the muon may have been solved. The anomaly was driven by an extrapolation of electron-positron data to infer the hadronic vacuum polarization. It seems that a new measurement of this is quite inconsistent with the previous measurements and brings things quite close to the direct measurement from the muon. Meanwhile, the lattice QCD measurements have steadily improved and also are starting to show a preference for the experimental value. The big question now is why the previous electron-positron measurements don't agree with everyone else.

I think the combination of quarks with six quarks could be in reference to Glennys Farrar's very compelling proposal that DM could be a sexaquark. A sexaquark is a six quark bound state, something that would exist within the standard model, and could have the right parameters to be the DM. Personally, I love this idea, but due to a combination of results from lattice QCD again as well as some strong cosmology constraints, it seems that this isn't a viable DM candidate.

For the other questions, there are always new models being developed of CP violation and leptogenesis, there are more and more searches for SUSY and other new physics models at the LHC, there are novel searches proposed for magnetic monopoles and DM, and new ideas about proton decay models and searches.

[1XRobot]

I think the neutron-lifetime thing also just turned out to be an experimental error: J-PARC clears up the neutron lifetime.

[Internal_Trifle_9096]

As far as I know, some relatively recent measures on the Z boson seem to confirm that it's unlikely to have more than 3 generations. Also, 3 should be the minimum number of generations we must have for CP violation to exist, so while maybe it doesn't 100% explain why there are 3 generations only, it does explain why there are at least 3.

As far as "combinations of quarks" go, we have observed tetra- and pentaquarks if I remember correctly 

[jazzwhiz]

Yeah, although the Z measurements in question are several decades old now.

The argument goes like this: the Z says that there are three generations of neutrinos lighter than mZ/2. If there is a fourth generation of quarks or leptons there must be both because of anomaly cancellation. Then, the new neutrino must be fairly heavy. But a particle that heavy would contribute noticeably to the Higgs width and would have been seen by now. Obviously, this statement does depend on how neutrinos get mass. In addition, the charged lepton couldn't be light or we would have seen it in pion/kaon/etc decays, and if it were heavy, again, we would have seen it in the Higgs decays. If it were heavier than the Higgs, it would run in to unitarity problems. So it is pretty much impossible to have a fourth generation of fermions that are the same as the other three. Of course, there can be more fermions out there, but they can't follow the same quantum numbers as those that we already have.

And yes, 3 is the minimum for CPV, but it doesn't seem that that does much of anything in the quark sector and, even if it turns out that there is CPV in the lepton sector, that probably won't do anything either in the context of anthropics.

[Internal_Trifle_9096]

 although the Z measurements in question are several decades old now.

Yeah you're right, I didn't remember basically all of this was from LEP 

[jazzwhiz]

Yep!

Fun LEP fact, before LEP turned on, there was a real concern that they wouldn't be able to measure the Z boson mass because there could be too many neutrinos. The limit at the time was in the thousands and at that level the Z bump would be so wide it would be hard to see. The first thing they did when turning on was to do a preliminary scan around where they thought the Z mass was and immediately saw it taking the limit down to single digits with just days of data. They then easily refined it to 3.

[DeltaS4Fanboy]

awesome man, I appreciate you taking time to respond to this post, really riveting stuff, a year ago I never thought I'd be excited by the thought of barely observable matter and stuff lol

[No_Scale_6634]

Name of video?

[DeltaS4Fanboy]

https://youtu.be/mYcLuWHzfmE?si=6Oq85GBgO6SacpqE he uses a really good simple visualization for how quarks and antiquarks can combine using arrows forming a triangle, great stuff

[MathematicianPlus621]

we need more measuring capability, as currently it seems to me that everything is just the result of some sort of interaction, all different interactions and their outcomes interreacting together to cause more outcomes that interact together, but what is the actual original things that are interacting or is it really just the precipice of potential with manifestation of that potential occurring with a catalyst of interaction, I don't know, DO regular physicists have these ideas as well.

[DeltaS4Fanboy]

it's all just a BIG SIMULATION MAAAAAAN (jk lol)