Questions tagged [quantum-chromodynamics]
Quantum-ChromoDynamics (QCD) is the quantum field theory believed to describe the strong nuclear force.
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Feynman rules with helicity states.
Whenever Feynman rules are stated they are always without any mention of the helicities - this I find to be very confusing. How does one introduce and account for that?
Is there an intuitive/simple ...
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Similar masses and lifetimes of the $\Delta$ baryons
Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
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Colour decomposition of $n-$gluon tree amplitude
I have here a $SU(N_c)$ Yang-Mill's theory and let the index $i$, label the $n$-gluons, and $\{k_i, \lambda_i, a_i\}$ be its momenta, helicity and colour index and $\cal{A}_n^{tree/1-loop}(\{k_i, \...
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Derivation of the effective potential between a quark and an anti-quark
Typically in particle physics books (not in QFT books!) I have often seen this statement that the potential between a heavy quark and its anti-quark can be "empirically" represented as $V(r) = -\frac{...
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buiding circuits from color superconductors
caveat: the sort of exotic matter engineering in here is currently beyond the reach of our technology, but, that having been said:
Has their been any research on building models of these sorts of ...
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Is the axial gauge with a $\xi$ term useful in Yang-Mills theory?
i) Do people use axial gauge with a $\xi$ term? When $\xi\neq 0$, ghosts do not decouple, but maybe it's still useful?
ii) Is it proved that the term $\frac 1 {2\xi}(n.A)^2$ in the Lagrangian does ...
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How to integrate over rapidity for Parton Luminosities in LHC?
I want to make a comparison of parton luminosities between Tevatron and LHC. According to Factorization theorem the cross section in hadron colliders, as long as the partonic cross section has $\hat \...
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Cusp anomalous dimension in QCD
What is the "cusp anomalous dimension", starting from the basics? I came across this term while reading some QCD papers.
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What is new with quark-Gluon Plasma and the bubble formed at RHIC?
RHIC experiment results of forming Quark-Gluon Plasma and a possible bubble was news few months ago. I cannot find any follow up news after that. Does anybody know anything new in this front? I am ...
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Phase diagram of simplified QCD
Consider QCD with a single generation of massless quarks (u, d). This is probably the simplest variant of QCD which bears some relation to the real world. The theory has the following exact global ...
Squark
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What does Gribov's last paper tell about coloured states?
In the first days of July 1997, after a long driving effort, crossing all of Europe to come to a meeting in Peñiscola, Vladimir Gribov fell fatally sick and he passed away one month later. His paper "...
user135
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Why isn't there heterotic holographic QCD?
I think the question speaks for itself... Top-down holographic QCD, like Sakai-Sugimoto, always involves the Type II string. There are one or two papers on hQCD using the Type 0 string. But I can't ...
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Can quark-gluon plasma ever be close to an ideal gas of asymptotically free quarks?
The question inspired by an upcoming colloquim at UCB.
A naive interpretation of quark asymptotic freedom seems to imply that at high enough energies they should be weakly interacting. On the other ...
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What's jet multiplicity?
That's a basic thing, but, surprisingly, it is very difficult to find concise explanation of:
What is the definition of jet multiplicity?
Why is it interesting?
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Why are the even and odd Regge trajectories degenerate?
This is an old classic which I don't think ever got a clear answer. The Gribov-Froissart projection that gives the relativistic version of Regge trajectories treats even angular momentum differently ...
