Recent content by ccnu

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    Graduate Can we sum out the vacuum state ##|0\rangle\langle 0|## ?

    For example, when we write down the operator definition of quark fragmentation matrix element: ##\Phi_{ij} = \sum_X \int d^4 x e^{ikx}\langle 0|\psi_i(x)|P,X\rangle\langle P,X|\bar{\psi}_j(0)|0\rangle##. Can we rewrite is as: ##\Phi_{ij} = \sum_X \int d^4 x e^{ikx}\langle...
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    Graduate How to Derive the Equality Involving u^s(p) and Spin 4-Vector?

    I think you can find the answer in Bjorken&Drell's famous book "Relativistic Quantum Mechanics", I remenber it's in the first few chapters.
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    Graduate How to describe the spin state of a massless particle?

    Is that to say, we can only use chirality to describe the spin state? No spin vector be involved?
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    Graduate How to describe the spin state of a massless particle?

    For a massive particle, say, an electron, we can use a spin vector ##\vec{S}## to denote its spin state, and the corresponding covariant four vector ##S^\mu##. And we have ##P \cdot S = 0## in the particle rest frame, so it holds in any frame for it is an Lorentz scalor. But, what if the...
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    Graduate Is there any groups working on FF's like CTEQ on PDF's?

    ff = fragmentation functions
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    Graduate Is there any groups working on FF's like CTEQ on PDF's?

    Oh, thanks! I searched "Matteo Cacciari" in inspire, and found "FastJet user manual". I know other softwares like Pythia, Herwig..., but they are event simulation tools. Are there any parameterization forms or any code packages about FF's like CTEQ does in PDF's case?
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    Graduate Is there any groups working on FF's like CTEQ on PDF's?

    I know some groups on PDF's like CTEQ, MSTW, NNPDF... Is there any groups working on the parameterization of fragmentation functions, and publish any codes that can be called?
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    Graduate Experiments and groups about the parameterization of PDFs & FFs

    Ok, I found some experiment on f(x) and D(x), but how about the transvers momentum dependent ones? That is ##f(x,k_\perp)## and ##D(x,k_\perp)##. Is there any experiment about it?
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    Graduate Experiments and groups about the parameterization of PDFs & FFs

    I want to do a survey about the parameterization of PDFs & FFs, and make a summary (say, in tables and figure) about the experiments and groups working on it, and their results. Where can I found these materials? Regards!
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    Graduate Why ##n^\mu T_{\mu\nu}## is called the pressure?

    Oh~~ yes, I forgot to say that ##n^0 = 0##, and ##n^\mu## is pure spatial. Thanks a lot!:smile:
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    Graduate Why ##n^\mu T_{\mu\nu}## is called the pressure?

    I read in the textbook which says that, according to the usual definition the absolute value of ##n^\mu T_{\mu\nu}## is just the pressure. ##T_{\mu\nu}## is the energy-momentum tensor and ##n^\mu## is a four dimensional normal vector.
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    Graduate About the gluon feild and propagator

    I am confused about the very step from Eq.(14) to Eq.(15) in the paper http://arxiv.org/pdf/hep-ph/0308157.pdf There is one ##ig## in (14), while ##(ig)^2## in (15), where does it come from? Regards!