Range of strong force as strength gets weaker.

[Spinnor]

Say we can set the strength of the strong force weaker, can the glouns then range further and further from a quark? Can we eventually get the strong force to look like the electromagnetic force as far as the range of the force is concerned?

Thanks for any help!

 

[Parlyne]

Sort of. And, no. For any non-zero QCD coupling, the strong force will be confining. But, as you turn down the coupling strength, the QCD bound states will tend to get physically larger. And, if you turn down the coupling strength far enough, fragmentation of QCD states becomes exponentially suppressed. With a sufficiently weak strong force you could, in principle, get macroscopic bound states. However, the range would never get to infinity.

 

[fermi]

...For any nonzero QCD coupling, the strong force will be confining...

Hmmm?? I think you express a general belief by a majority of the physicists, but I have never seen a proof of it. Can you refer me to an article where this is proven.

 

[Parlyne]

Hmmm?? I think you express a general belief by a majority of the physicists, but I have never seen a proof of it. Can you refer me to an article where this is proven.

So far as I know, there is no first-principles proof of this. However, my impression was that the presence of confinement can't be coupling-dependent. So, given that the strong force is seen phenomenologically to be confining, that should continue to apply to an identical theory no matter where you set its coupling.

 

[humanino]

If you forget about absolute mass scales from current quark masses, you still get dynamical chiral symmetry breaking and the generation of a scale from a growing of the perturbative coupling at long distances. Another way to say it, setting a lower coupling in QCD with massless quarks merely amounts to a change of scale : the coupling takes arbitrarily low values at high energies.

You can obtain confinement and dynamical chiral symmetry breaking with massless quarks for instance in instanton models of the vacuum.

At any rate, I think it is not controversial that QCD itself will still be confining whichever coupling you choose at a given scale. You just get a larger proton. But the issue is that if you make the coupling too weak, other interactions (electroweak) might become important.