Coulomb Singularity

[mariamskhan]

Hi all,
I am just new to work on NLO in QCD. I need to know how a Coulomb singularity in QCD is defined? What is the form/expression of this singularity term? Can anyone explain with an example of any Feynman diagram? I am interested in the case of a quarkonium with two gluons in final state. I'll be really grateful for the help.

[tom.stoer]

Can you explain what you mean by Coulomb singularity in QED?

[mariamskhan]

Coulomb singularity appears whenever a virtual gluon is exchanged between quark pair of a meson. The limit that relative velocity of these two quarks tends to zero (to make a bound state for meson) in an expression ~ 1/v (v being realative velocity here) generates this singularity. This is what I know so far. I'm not sure where does this expression ~1/v come from? :cry: And with this information, I think we have Coulomb singularities only in QCD, but not in QED. :confused:
Can anybody please help or refer me to some good derivation of this??? PLZZZZZZZZ

[tom.stoer]

I do not know about which model you are talking. QCD, low-energy effective XYZ, non-relativistic quark model, .... I have never seen 1/v in full QCD.

[mariamskhan]

Ooops, I really forgot to mention this. I'm talking about NRQCD.

[tom.stoer]

Ooops, I really forgot to mention this. I'm talking about NRQCD.
any references? on arxiv?

[mariamskhan]

here is one of the references:

http://pos.sissa.it/archive/conferences/032/098/LAT2006_098.pdf