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    SU(3)xU(1) breaking exercise?

    Hello, don't you have similar example from dynamical breaking of chiral QCD ?
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    Higgs excluded at 170 GeV (press release 4 August)

    Hello, if you look at the bottom figure from this web page : http://tevnphwg.fnal.gov/results/SM_Higgs_Winter_08hepex/ you will see a plot drawing 95% exclusion limit/SM. As long as this number is > 1, you cannot exclude the point. To summarize this plot, the higher is this number, the...
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    Detecting Quarks

    When you shoot two protons against each other, if protons were elementary particles, you would observed two scattered protons after the collisions (I'm simplifying). Instead of that, we observe what we call two "jets" back to back + some remnants. Jet is a collimated flux of hadrons particles...
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    Dark Matter and supersymmetry

    Be careful dark matter and dark energy are different. If I remember well, dark matter is roughtly ~ 22% of universe mass, and dark energy ~ 73%. Supersymmetry provide indeed a candidate for "cold" dark matter (heavy matter with low speed). usually, because there are plenty of supersymmetry...
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    Higgs excluded at 170 GeV (press release 4 August)

    Hello, it is much easier to exclude an Higgs at 170 GeV than at 120 GeV for both Tevatron and LHC. Just because around that energy H -> WW* which is much easier to check than low energy signatures. High energy higgs (> 170 GeV) are also quite easy to discover/exclude due to H -> ZZ -> llll...
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    Energy reconstruction in calorimeter

    Hello Kenith, you might be interested by this (rather old) paper about jets building at Tevatron : http://arxiv.org/PS_cache/hep-ex/pdf/0005/0005012v2.pdf In particular, in section 2, they explains with drawings collinear and infrared instabilities on jets.
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    Soft particle

    Hello, depends on the context. But it can be "soft Pt particle" ! Gamma can be the width of the resonance of an unstable particle (like a Z boson). Within the scheme c=h=1, you can choose arbritraly to express lengths, times, energies with a single unit (like GeV).
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    What quanta mediates the nuclear forces?

    Ok thanks... Looking back to my old courses, indeed I found something like \frac{\delta^{ab}}{k^{2} - i\epsilon}(g_{\mu\nu} - (1-\varsigma)(\frac{k^{\mu}k^{\nu}}{k^{2}}))
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    What quanta mediates the nuclear forces?

    Hello Jon, thanks for the link. Looking a bit at the article, I have a naive question : what does the assumption \lambda^{a}D^{ab}\lambda^{b} \rightarrow \lambda^{a}G(x-y)\lambda^{a} come from ? Is it this line which means that we have colorless objects as a first assumption ?
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    What quanta mediates the nuclear forces?

    Can we really go through this analogy between nuclear forces and Van der Waals as we often hear ? I mean I understand there is a charge cancellation in both cases and so we are only sensitive to higher order effects. But, as QCD is highly non-perturbative in this energy domain contrary to QED...
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    What is charge? Why do fundamental particles possess it?

    Yes why ? The yukawa coupling between higgs and fermions do not look really quantized. Why electric charge is ? And why is it such that it cancels prefectly eg anomalies ? Can it be explained in GUT theories ?
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    Left spinors in GUT theories

    I do not know much about GUT theories, but it might be related to the fact we often have majorana particles and it is easier the formulate the them with left spinor, anti-particles and conjugate than with left and right spinors ? In any case, if you learn about the answer, I am interested...
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    Gauge invariance and it's relation to gauge bosons

    fermion mass terms in the lagrangian m\bar{\psi}\psi are scalar. Maybe you should try to rewrite this term as a function of \psi_L and \psi_R ?
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    Quark vs. Hardron mass

    Thanks ! That model looks interesting. Hope some day nuclear physicists can run a big simulation with Lattice QCD to check 2 nucleous hypothesis.
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    Quark vs. Hardron mass

    Spin or isospin, the question remains : where this short repulsive force is coming from ?
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    Quark vs. Hardron mass

    Thanks, I found some interesting information on wikipedia : http://en.wikipedia.org/wiki/Internucleon_interaction but they do not explain shot distance repealing. Pauli principle should not exclude having two nucleons with opposite spins at the same position. They were not talking about...
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    First Evidence of New Physics in b <-> s Transitions

    There is a new ph paper on this Bs excess related to SUSY : http://arxiv.org/PS_cache/arxiv/pdf/0803/0803.1898v1.pdf [Broken] In this paper, they introduce R-parity violation to explain both Bs and Ds->lnu excess. The only problem now I guess is that SUSY has no more any dark matter candidate ...
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    Quark vs. Hardron mass

    Hi, do we explain why nucleon-nucleon potential becomes repulsive at very short distances ? Or is it only phenomenologic ?
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    Radiotracer Decay - What's Left?

    Hello Chyral, I would say that the recoiling of the nucleus is negligible (specially for F) wrt the energy of positron-neutrino pair. In some way, that's why you can do imaging.
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    Top coupling = 1 + corrections

    Hello arivero, I'm not theorist so I have only basic comments/questions. Why so "hugely" different ? m_top/m_charm is same order as m_charm/m_up. So if you wonder why m_top/m_charm is large, you should wonder the same about m_charm/m_up. I would rather turn the sentence the other way...
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    Higgs field

    Hello humanino, I have a question about this topic. If quarks were massless (gedanken experiment), then wouldn't pions be massless (goldstone bosons) ? Thas would mean in that case we would have a composite massless particle which is not so common in our present knowledge of the world ?
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    Top coupling = 1 + corrections

    Thanks, so m_top ~ vev/sqrt(2) ... But why this normalization is advocated ? Naturalness argument ?
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    Top coupling = 1 + corrections

    Hello, I knew top-higgs yukawa coupling was ~ m_top/vev with Vev ~ 246 GeV. So how do you come to this 0.9914 value ? Thanks.
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    First Evidence of New Physics in b <-> s Transitions

    Hello, but what you describe, isn't it Minimal Flavor Violation which seems disfavored by this measurement ?
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    First Evidence of New Physics in b <-> s Transitions

    First Evidence of New Physics in b <--> s Transitions Hi, please look at the following arXiv : http://arxiv.org/abs/0803.0659 First Evidence of New Physics in b <--> s Transitions Authors: UTfit Collaboration: M. Bona, M. Ciuchini, E. Franco, V. Lubicz, G. Martinelli, F. Parodi, M...
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    Can a neutral pion decay to a neutrino and an anti-neutrino?

    Hello, Your argument looks sensible (why no weak charge ? I would say only T_3 = 0) but I'm not sure to understand it completly. Looking at http://doc.cern.ch//archive/electronic/hep-ph/0501/0501117.pdf , it seems that pi0 -> Z -> nu nubar vanish only for massless neutrinos.
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    Higgs field

    I would rather say the opposite. During EW symmetry breaking, 3 components of the Higgs doublet (the goldstone bosons) are eaten by W and B fields resulting in massive W and Z. Yes, the vacuum expectation value (vev) through yukawa terms added by hand gives mass to fermions. So on one side...
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    Can a neutral pion decay to a neutrino and an anti-neutrino?

    Hello Vanadium, GIM mechanism start to be old for me last time I studied it. I understand that for K0 we have FCNC, but why can't we have : u ubar + ... -> Z0 -> nu nubar ? This diagram is suppressed by mnu/MZ, but why do we need CKM and stuff like that ? Can you explain a bit more ?
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    Can a neutral pion decay to a neutrino and an anti-neutrino?

    Hello, what do you mean by GIM suppressed ? From PGD, existing limits are : Br(pi0 -> nunu) < 2.7e-7 Br(pi0 -> nunugamma) < 6e-4 I have no idea, how much we should expect from SM theory, do you know ?
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    Antimatter/matter Question

    Generally speaking, many physicists do not answer questions starting by "Why"...
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