Recent content by Yustas

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    Graduate Standard Model: Lagrangian vs. Hamiltonian

    Doesn't matter, they are related by a canonical transformation. Depending on the situation you use one or another: for canonical quantization one uses Hamiltonian formalism, for path integrals -- Lagrangian.
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    Graduate About hierarchy problem of higgs mass

    No, beacon is right -- there are no power divergencies in the dimensional regularization with mass-independent subtraction like MSbar. That's why it's used in effective field theory calculations (chrial PT, etc), as it does not spoil power counting by introducing unwanted mass scales. The...
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    Graduate Is there any evidence for a 4th family of particles?

    Sure. Well, it's stil going to be a bit handwaving. First, let's compute the rate for the eak decauy of top quark (t -> b W). The width would come out to be approximately 2 GeV: \Gamma_t \sim \frac{G_F}{\sqrt{2}} \frac{m_t^3}{8 \pi} \sim 2 ~GeV This implies that the lifetime is \tau \sim...
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    Graduate Is there any evidence for a 4th family of particles?

    Toponium (top-antitop meson) is not observable because top is too heavy to form a bound state. Simplistically speaking, top quark would decay faster via weak interaction than the time needed for "top-antitop system to make one revolution around each other" (note quotes), i.e. boundstate...
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    Graduate Is there any evidence for a 4th family of particles?

    In principle, one can avoid anomaly cancellation requirement if 4th generation quarks are not like the ones from the previous three generations (for example, with vector-type couplings, not chiral)... but it looks ugly to me, even though some people like it. Of course, 4th generation...
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    Graduate Is there any evidence for a 4th family of particles?

    Thanks Jeff!
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    Graduate How Do Neutrinos Differ from Anti-Neutrinos?

    Helicity is not a good quantum number for a massive particle (like a neutrino). Since it is roughly speaking defined as a projection of a particle's spin onto its momentum, one can always switch to a reference frame that is moving faster then the particle. In this frame you'll observe opposite...
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    Graduate Does a particle annihilate only with its corresponding antiparticle

    Photons do not annihilate because they do not interact directly -- there is no such term in the QED lagrangian. On the other hand, total aanihillation of neutron and anti-neutron is as likely as the annihilation of proton and anti-proton -- you have to arrange for interaction of three...
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    Undergrad Strong Nuclear Force and Electrostatic Force

    To answer the original question, nuclear force has a property of "saturation" related to the short-range nature of it mentioned earlier (classical analogy: if you have many marbles in a sack and ask a question how many marbles will any given marble touch at one time, the answer will always be...
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    Graduate Is a Goldstone boson identical to a Nambu-Goldstone boson?

    A majoron is a goldstone boson by construction since it comes from the spontaneous breaking of a symmmetry (as any goldstone boson).
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    Graduate Is there any evidence for a 4th family of particles?

    No, what I'm saying is that if 4th gen exists these couplings should be very small (such that V_t'b Vt'd m_t'^2 times usual hadronic stuff for t' contribution to B-Bbar mixing parameter \Delta m_B is smaller then current theoretical and experimental errors), not necessarily zero. So it would...
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    Graduate Is there any evidence for a 4th family of particles?

    4th generation quarks are searched for by studying the processes like B-Bbar (D-Dbar, K-Kbar) mixing and flavor-changing neutral current transitions, where 4th generation affects the mixing/decay parameters via loop diagrams. So far, everything is fine without the 4th generation (agrees with...