Symmetry between up and down quarks is more broken than expected

Working like that, it sounds like the standard model can explain literally anything...

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.

Well, it's intended to explain everything so, y'know.

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).

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.

Compared to explaining anything, explaining everything explains almost nothing.

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.

thank you! one day I'll understand this stuff - I skipped the qft elective at uni, but I'm trying to learn more now.

'The standard model' also doesn't include gravity. And we do have pretty good theories about gravity.

So it's definitely not the 'sum total of human knowledge'.

Can’t you just run the heuristic over many many runs to build up a probability model? i.e given we simulated a trillion times while varying inputs and we got marginal error, we’re 99.99999% certain that this function follows what we observe 100% of the time etc?

Does particle physics include gravity now?

Sorry, I missed that.

But yes in a sense: we do know that particles are subject to gravity. So that is part of 'the sum total of human knowledge of particle physics.'