Physicists make most precise measurement ever of the proton's magnetic moment

Re:Physicists make most precise measurement ever of the prot... by ahh on Sunday November 26, 2017 @03:01PM (#15782678)

(Disclaimer: not a QCD expert, but I did read a paper or two back in grad school from the perspective of someone who liked numerical linear algebra. Don't rely on this advice.)

I believe the core difference here between QCD and QED (the classical perturbative QFT) is that QED has a very small coupling constant (it's the fine structure constant, so ~1/137) whereas QCD has a large one (comparable to or greater than one.) It turns out that a perturbative expansion is effectively in powers of the coupling constant, so QED expansions converge rapidly...and QCD expansions converge not at all.

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Re:Physicists make most precise measurement ever of the prot... by ISL on Sunday November 26, 2017 @03:34PM (#15782825)

This explanation ought to be correct at low energy, just where most LQCD work occurs (attempting to predict even lower-energy observables, like the proton mass, etc.).

At high (collider) energies, it is okay to work perturbatively.

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