# Tag Info

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The hypercharge of a doublet cannot be "deduced". When one builds a gauge theory, the first step is to define the particle content of your theory and to postulate the representation of all particle multiplets. In particular, if the gauge group is abelian, then we have to assign numbers usually called charges. So, I reformulate your question: Why do we ...

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Virtual particles are not real It's in the name. You may draw Feynman diagrams where there are internal lines, and we call these internal lines virtual particles. They are not real. You will never detect a virtual particle. They are not really exchanged between the real charged particles. Virtual particles are a just-so stories designed to explain Feynman ...

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There are 5 standard model (SM) multiplets per generation of fermions. The SM gauge group is $\mathcal{G}_\text{SM} = SU(3)_C \times SU(2)_L \times U(1)_Y$. Various multiplets can then be written as $\mathcal{G}_\text{SM} \ni x = (C,T)_{(Y)}$, where $C$ denotes colour multiplet, $T$ weak isospin multiplet and $Y$ hypercharge value. Multiplets (1st ...

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You have noticed already that $$\mathcal{L}_{mass}\propto \left[g^2(W^1_\mu W_\mu^{1}+W^2_\mu W_\mu^{2})+(gW_\mu^3-g^\prime B_\mu)^2\right]$$ with the kinetic terms for $W^{i}_\mu$ and $B_{\mu}$ canonically normalized. Therefore the neutral linear combination of $W^3_\mu$ and $B_\mu$ that gets mass is proportional to $(gW_\mu^3-g^\prime B_\mu)$ and the ...

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One argument could be the Yukawa coupling, which is responsible for the coupling to the fermions. In the Yukawa coupling term in the Lagrangian, $\mathcal{L}_{\text{Yukawa}}$ , there are no terms that contain a $\gamma^5$ matrix, defined as $$\gamma^5 := i\gamma^0 \gamma^1 \gamma^2 \gamma^3$$ This publication states how terms in the Lagrangian transform ...

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The history of high energy physics is in the words "high energy" . There are two ways to get it, building higher and higher energy accelerators or studying cosmic rays, which last has answers in another question. Accelerators are of two types, those creating beams of particles that fall on fixed targets, and colliders, having two beams collide. All ...

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As pfnuessel said in his comment: The first thing to look at was the Higgs - there were hints from LEP and Tevatron, but no evidence, so the LHC was designed that the (SM-)Higgs has to be seen, if it exists. And for everything beyond the Higgs - we don't know! There are various theories, e.g. the different flavors of super-symmetry and others, but they all ...

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No, only some baryons form a decuplet under SU(3) flavor symmetry, specifically those 10 spin 3/2 baryons formed from up, down,and strange quarks,depicted in the following diagram (figure credit Wikipedia baryon article , figure listed as public domain): On the diagram $Q$ is electric charge, $I_3$ is isospin, and $S$ is the strangeness quantum number. ...

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It is not an assumption; both $0^+$ and $0^-$ were considered as possible Higgs states. The angular distribution of decay products (like in $h\to ZZ$, $h\to f\bar{f}$, $h\to \gamma\gamma$ or in Higgstrahlung) is dependent on the parity of the Higgs particle. Alternatively, you can measure the helicities of the outgoing photons (in the $h\to\gamma\gamma$ ...

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It doesn't matter whether the $b$-quark is highly energetic, it can never decay to a top quark and a $W$-boson if it is on mass shell, by which I mean, $p^2=E^2 - \vec p^2 =m_b^2$. To see this, consider energy-momentum conservation, $$b^\mu = W^\mu + t^\mu \Rightarrow m_b^2 = M_W^2 + m_t^2 + 2W\cdot t = M_W^2 + m_t^2 + 2 E_t M_W$$ However, since the energy ...

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The answer to the question is yes. The framework of quantum field theory allows one to describe all interactions except for gravity. Different realizations of QFT take account for different fields of physics: For example, phenomena of electromagnetism are described accurately by quantum electrodynamics, while the strong interaction that describes how nuclei ...

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A quick clarification: quantum field theory is a classification of theories, that is there can be many different quantum field theories. The Standard Model is an example of a quantum field theory, and it does indeed describe all the phenomena we know about except for gravity. You might be interested to read this summary of the current (well, current as of 18 ...

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