[HN Gopher] Symmetry between up and down quarks is more broken t...
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Symmetry between up and down quarks is more broken than expected
Author : terminalbraid
Score : 66 points
Date : 2025-03-29 10:12 UTC (2 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| bananapub wrote:
| or you could just link to the actual press release from Actual
| CERN?
|
| https://home.web.cern.ch/news/news/physics/symmetry-between-...
| ptsneves wrote:
| What are the consequences for this breakage? The article says
| current models do not easily fit the asymmetry but does not state
| what parts of our understanding will break if those models are
| wrong.
| fpoling wrote:
| Strong interactions are notoriously difficult to calculate from
| the first principles. So typically it is not done, but rather
| theoreticians try to guess the result and use the experimental
| data to partially fill the calculation gaps.
|
| So I expect in this cases the guesses were wrong and the
| Standard Model will manage to explain that as well.
| staunton wrote:
| Working like that, it sounds like the standard model can
| explain literally anything...
| exe34 wrote:
| the standard model isn't one thing, it's the sum total of
| human knowledge of particle physics. it's an equation with
| a gazillion terms - this is an adjustment to one of those
| terms. and yes, you can add terms for any new physics you
| discover, so technically you're right, but it's not a
| gotcha.
| yummypaint wrote:
| This makes it sound more ad hoc than it is, it's not some
| polynomial where people just tack on terms.
|
| In its current agreed upon form it's just
| SU(3)xSU(2)xU(1). This gauge symmetry defines the
| lagrangian, which has 19 parameters to be determined by
| experiment.
|
| It's true that this isn't the whole story (dark matter
| etc), but these symmetries are physically motivated and
| their predictive power is pretty amazing (the QED part is
| CORRECT as far as any experiment has been able to check
| so far).
| exe34 wrote:
| thank you! one day I'll understand this stuff - I skipped
| the qft elective at uni, but I'm trying to learn more
| now.
| mystified5016 wrote:
| Well, it's intended to explain _everything_ so, y 'know.
| tines wrote:
| Compared to explaining anything, explaining everything
| explains almost nothing.
| fpoling wrote:
| So far nobody expected this effect so no attempts were made
| to derive at least the bounds on it from the first
| principles. With strong interactions it may require a lot
| (like many man-years) of efforts, but it will be eventually
| done if no plausible explanation can be given using semi-
| experimental models.
| jerf wrote:
| It's not as bad as that. AIUI, the essence is, if you've
| ever seen the concept of a Feynman diagram and summing over
| all possible interactions, that works well for
| electromagnetism and some other interactions because the
| alternative terms fall off very quickly. For the strong
| interaction, they fall off so slowly that it takes massive
| amounts of computing power to walk through all the
| alternatives, essentially infeasible amounts of it. So we
| have to use some heuristics. If it turns out one of our
| heuristics was wrong, well, that's actually happened a
| number of times before.
|
| So it's not quite as bad as "you just hit the model until
| it says what you want it to say". It's more "your shortcut
| broke so take less of a shortcut and you may discover that
| the standard model worked better all along than your
| shortcut". Which, again, has already happened multiple
| times.
|
| In fact it is quite frustrating to physicists that the
| standard model always wins these fights. They'd love for it
| to break in some concrete manner, which is why they're
| always going on about this break or that break. As it
| stands now, in some sense, every time the standard model is
| vindicated it's a worst-case scenario for particle physics.
| It's not like there's a cartel trying to defend it...
| _everyone_ would love to be the one who definitively broke
| it! It 's virtually a guaranteed Nobel prize.
| facile3232 wrote:
| > Strong interactions are notoriously difficult to calculate
| from the first principles.
|
| ??? Where does empiricism come in? Surely you need some kind
| of data to feed even raw assumptions. Maybe I'm just
| misinterpreting how "first principles" is employed here.
| nine_k wrote:
| In particular, it's interesting if that may have help explain
| the prevalence of matter over antimatter around us.
| tsimionescu wrote:
| If the models are really wrong in a fundamental way and this
| can't be fixed by some tweaks in the free parameters (and this
| is a BIG if), then it's hard to predict what the consequences
| might be: the model is wrong, in a way that hasn't been
| extensively studied. How different a correct model might be is
| hard to predict.
| ars wrote:
| BTW isospin is actually how many up vs down quarks they are. It's
| not a fundamental property like spin or charge.
|
| It's an old term that was created before they knew that up and
| down quarks existed.
|
| Personally I find the term outdated because there are 4 other
| quarks, and isospin only talks about two of them.
| floxy wrote:
| https://www.youtube.com/watch?v=esayi49OAk4
| westurner wrote:
| Isospin symmetry: https://en.wikipedia.org/wiki/Isospin
| #History :
|
| > _Isospin is also known as isobaric spin or isotopic spin._
|
| Supersymmetry: https://en.wikipedia.org/wiki/Supersymmetry
|
| Does the observed isospin asymmetry disprove supersymmetry, if
| isospin symmetry is an approximate symmetry?
| dudu24 wrote:
| This misses the point of isospin. Isospin is an approximate
| SU(2) symmetry due to the fact that the up and down quarks (the
| "light" quarks) have very similar masses compared to the rest
| of the quarks, so they can be approximated as two different
| eigenstates of the same particle. It's mathematically identical
| to the SU(2) symmetry of a spin-half particle. The reason it
| doesn't include the other quarks is because they are so much
| more massive.
| 1970-01-01 wrote:
| Just gluon the broken symmetry and nobody will notice :)
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