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1

I know this is a year old question, but I am going to attempt an answer. As far as I can tell, this is not really a caveat. The reason for this is that I can always set the overall phase of the quark mass determinant to be zero with a chiral U(1) transformation. For a discussion of this see for example the chapter on theta vacua in Weinberg's QFT book. The ...


3

You state your age as 13, and it is not clear how much you know about elementary particles and interactions. This is the table of elementary particles in the standard model of physics And these are the forces with which the elementary particles interact and finally create matter as we see it everyday. The quarks within the proton and neutron interact ...


0

The second one is a "quark diagram" or "quark model diagram". These are not 'true' Feynman diagrams, as they only represent the quark fields. The gluon field is implied, and it's an exercise for the reader to fill in the gaps. The only pedagogical source I can find is this: http://ned.ipac.caltech.edu/level5/Cottingham/Cott1_5.html (See the caption of ...


1

In your second diagram, there is implicitly a gauge boson source of your $q\bar{q}$ pair production. It could be a gluon, a photon or a $Z^0$. This gauge boson has to be attached to something, reasonably your single quark leg as in the first diagram.


1

If your theory is anything like scalar-QCD then the gauge field couples to the scalar current through a "derivative" interaction $$A^\mu J_\mu \supset A^\mu \; \left( \phi^\ast \partial_\mu \phi - \phi \partial_\mu \phi^\ast \right)$$ This would mean that each of the gauge-boson scalar vertices will have a factor of the scalar momentum, in the numerator. ...


0

Well, quark anti-quark pair can be created by a photon in a process like $$ \mu^- + \mu^+ \to \gamma \to q + \bar{q} \,,$$ which is just the time reversal of a typical Drell-Yan process, with the intermediate photon shown explicitly. Not sure if this really answers your question since you seem to be assuming a single quark initial state.


1

Boy, that term gets thrown around in a number of ways. In a MC generator context it sometimes means "everything but radiative corrections", but I don't know if that is the way the authors of Pythia mean it. On that assumption a "second hard process" would be a final state interaction that is modeled separately of the corrections; re-scattering in a ...


0

You can compute the feynman rule for the $\phi$-$\phi$-$\chi$ vertex by taking $$e^{-i \int \mathrm d^4x L_\mathrm{full} }\frac{\delta}{\delta \phi^a} \frac{\delta}{\delta \phi^b} \frac{\delta}{\delta \chi^c} e^{i\int \mathrm d^4x L_\mathrm{full}}$$ where $L_\mathrm{full}$ is the sum of the free and interaction Lagrangeans and afterwards remove any ...



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