# Tag Info

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The problem with "weak charges" is that electroweak symmetry is spontaneously broken. Before the symmetry breaking, electroweak symmetry is described by an $SU(2)_L \times U(1)_Y$ gauge group.This amounts to three charges: weak hypercharge $Y$ for $U(1)_Y$ and weak isospin (total isospin $T$ and third component $T_3$) for the $SU(2)_L$. Some examples of ...

7

You're mixing a few things up here. When you say "three" for the strong force, you're counting the number of colors of quarks, but when you guess "three" for the weak force, you're counting the number of force carriers. These are two different things. For example, if you counted the number of gluons (the force carriers for the strong force), you'd get ...

6

When e.g. a neutron decays, there is no "real" W-boson inside, in the sense that it could be detected at every point. Instead, the decay of the neutron involves a "virtual" W-boson, a W-boson that only exists for a very short time. Quantum mechanics allows the energy conservation law to be violated by $\Delta E$ for a very short time $\Delta t$ as long as $\... 5 To add to the other answer: Your intuition is right in a way. The fact that the$W$and$Z$bosons are so heavy is the reason for the weakness of the interaction. For example,$\pi^+$mesons can decay over the weak interaction, the process is described by the following Feynman diagram: According to the Feynman rules, the probability amplitude of such a ... 5 OK, since my name was taken in vain I suppose I am obliged to clarify my comment further. My invitation was to contrast charge oscillations to strangeness oscillations in the$K^0-\bar{K}^0$system, not to use the latter to argue for the former. The finally mutated question I am addressing is “Why are there no charge oscillations and superpositions of ... 4 I would say two, which is pleasantly consistent with the$SU(2)$structure of the weak force. One is the coupling strength with the$Z$boson, and one is the weak isospin which is raised and lowered by the$W^\pm$. 3 If a particle changes flavor, it's a charged-current weak decay. Example:$n\to pe\bar\nu$. If there's a neutrino in the final state, it's a weak interaction. Decay example:$\pi^+\to\mu^+\nu$. See also neutrino scattering. If parity isn't conserved, it's a weak interaction. Examples:$K^0 \to 2\pi$and$K^0 \to 3\pi$. Note that kaon decays and$K\...

3

If you take an electron and a proton there is a strong electromagnetic force between them because the electron has a charge of $-e$ and the proton has a charge of $+e$. However suppose you combine the electron and proton into a hydrogen atom. The hydrogen atom has a net charge of zero so there is no strong electromagnetic force between two hydrogen atoms. ...

3

Representation of $SU(2)$ is pseudo-real. Which means, if $\mathbf{[2]}$ and $\mathbf{[\bar{2}]}$ are the fundamental and anti-fundamental representation of $SU(2)$, then there exists an anti-symmetric matrix $\cal{C}$, which connect both of them, as $\cal{C}\mathbf{[2]}\cal{C}^{-1}=\mathbf{[\bar{2}]}$. Another way of saying this, both $\mathbf{[2]}$ and $\... 2 Because "spontaneous symmetry breaking" does not actually break any symmetries. This is a pretty important principle that is not always adequately taught. In spontaneous symmetry breaking the symmetry in question is always a full symmetry of the theory. The difference between a spontaneously broken symmetry and an unbroken symmetry is just in how the ... 2 There is the statement in the video, "particles vibrate", and vibrations lead to the concept of frequency. The confusion comes because in fist quantization, the solutions of the Schroedinger and Dirac equations, the wavefunctions have a sinusoidal dependence, which lead to a probability density distribution for the particles, and the de Broglie wavelength ... 2 It is not true that scale invariance requires strong interactions. After all, free scalar field theory is scale invariant (and so is classical electromagnetism). In high energy interactions approximate scale invariance emerges because asymptotic freedom implies that free field theory is indeed a useful starting point. QCD is subtle because we cannot study ... 1 The gauge symmetry group associated to the SM is$SU\left(3\right)_{c}\times SU\left(2\right)_{L}\times U_{Y}\left(1\right)$. Then we can not build the lagrangian of the SM with terms of the form$m\bar{\psi}\psi\$ because they are not gauge invariant. A term of this kind mix the right and left handed parts, which transforms differently. In order to give mass ...

1

Some care is needed when talking about quantum fields because they are a mathematical formalism for describing the properties of particles, and it is unclear to what extent a quantum field can be regarded as a physical object. Many of us are guilty of sloppy terminology such as the energy of a quantum field or transfer of energy betweebn quantum fields. ...

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The forces entering the standard model all are symmetric, with zero mass exchange particles at high energies before symmetry breaking. It is one of the beauties of the standard model. Any proposed model for further complexity , preons etc has to predict phenomena which are outside the standard model and at the same time, incorporate the phenomena which ...

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This is related to the so-called "colour charge" carried by particles involved in strong interaction. Although at first it was proposed to allow same quarks exist inside the baryons (despite Pauli exclusion principle), it is also used to describe the ability of hadrons to be free of confinement — only colourless particles (or white) can be free. This is not ...

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Who forbids me to think that the particles are not equipped with a primitive form of identity that arises intelligently to your measurements and you can not behave as a quality? "arises intelligently" is not in the physics domain. It is metaphysics, this assigning intelligence to particles, and there exist such metaphysical "theories" but their ...

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The CKM, PMNS matrices are mathematically absolutely analogous, except that the values and even hierarchies of all the parameters are entirely different in the two cases. (Also, we don't know whether right-handed neutrinos exist and whether the effective Majorana masses may be derived from Dirac masses or something else.) But both matrices may be reduced to ...

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@Michael Brown is right. The SM has 12 exactly conserved charges. All local invariances, a fortiori also imply global invariances, if you ignore (for the sake of argument) the spacetime variability of transformation parameters/angles. So SU(3) has 8, not 3 conserved charges, RG, BG, .... The group has 8 generators. Likewise, SU(2) has 3, not 2 conserved ...

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