Strong Nuclear force (Yukawa's interaction Vs QCD)

[ghery]

Hello:

I've heard that Yukawa's interaction could explain the nuclear force, but I also heard that the strong nuclear force is explained by QCD, Could you please explain me more about it ?

Thanks a Lot

 

[malawi_glenn]

The underlying theory of quark-interaction is QCD, that was before Yukawas theory of meson exchange interaction. Yukawas theory could explain some features of the nucleon-nucleon interaction, but not satisfactory.

However, there are many problems how to go from QCD to Forces between hadrons.

i) Coupling constant of QCD becomes so large in the energies you have in hadron physics so you can't do a perturbative expansion in terms of the coupling constant of QCD (just as you would do in QED and in high energy QCD).

ii) The force between quarks are due to their colour charges, but hadrons are colourless..

However, effective field theories have been developed the last 20years or so, the most famous is Chiral Perturbation Theory.

Just because we know the theory of electrons and atoms, doesn't mean that we understand the behavior and properties of solids. The same analogy holds here too.

This is the best link I can give you to Forces between hadrons as explained by Chiral Perturbation theory: http://arxiv.org/PS_cache/hep-ph/pdf/0210/0210398v1.pdf ( I study that document myself, are doing my master thesis in hadron physics)

But you might want to start to read this short guy first: http://en.wikipedia.org/wiki/Chiral_perturbation_theory :-)

 

[Orion1]

The Yukawa interaction is an interaction between a scalar field and a Dirac field.

The Yukawa interaction can be used to describe the strong nuclear force between fermionic nucleons mediated by pseudoscalar mesonic pions.

It is the interaction of the 'residual' strong nuclear force which binds a nucleus.

The Yukawa interaction is also used in the Standard Model to describe the coupling between the Higgs field and massless quark and electron fields.

Reference:
http://en.wikipedia.org/wiki/Yukawa_interaction"

 

[malawi_glenn]

That is correct Orion1, but only the long range-part of the Yukawa interaction can be done in that way. Then you must include more meson fields, like phi-mesons, omega-mesons & 2pion exchange etc. But that don't solve the problem either, so a effective field theory approach is more friutful ("residual interaction").


Also, the Yukawa interaction is between point-particles (elementary particles), but hadrons are not point particles... one more source of error :-)

 

[jtbell]

Here's my understanding of the relationship between the Yukawa force and QCD, which is probably oversimplified.

Yukawa's theory explains the interaction between nucleons (neutrons and protons) in the nucleus as being caused by the exchange of virtual particles that we now call pions.

As we now know, nucleons are made up of quarks. QCD explains the interaction between quarks as being caused by the exchange of virtual gluons.

The nucleon-nucleon Yukawa interaction can be explained as a "residual" interaction from the quark-quark interactions of QCD, similarly to the way that the atom-atom van der Waals interaction can be explained as a "residual" interaction from the electron-nucleus interaction. At least I think this can be done in principle. I don't know how well people have actually been able to work it out.

 

[Lester]

Indeed, Yukawa model is the low-energy limit of QCD reducible yet to a Nambu-Jona-Lasinio model. Quanta are not pions or other mesons but possibly glue excitations. See

http://arxiv.org/abs/1002.4600