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17 votes
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How many kinds of "weak charges" exist?

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 ...
Bosoneando's user avatar
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16 votes
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Are electroweak particles stable?

It's isn't terribly meaningful to say that Photons made of the electromagnetic force or that the W and Z bosons made of the weak force, though it's certainly true that these particles are the gauge ...
John Rennie's user avatar
12 votes

How many kinds of "weak charges" exist?

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 ...
knzhou's user avatar
  • 102k
12 votes
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Why is the electron massless before interaction with the Higgs field?

I have several answers on this site detailing the issue, but it is too hard for me to collect them all. Your source might be this mini-crib-sheet. In a nutshell, as any half-decent QFT course should ...
Cosmas Zachos's user avatar
11 votes
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Why $U(1)_Y$ hypercharge rather than $U(1)_\text{em}$ electromagnetism?

Short answer: to accurately model reality. Long answer: The weak interaction has several peculiar properties: The $W$ bosons are vector bosons (so the weak theory is likely a gauge theory) The $W$ ...
Luke Pritchett's user avatar
11 votes
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Is the right-handed electron really an $SU(2)$ singlet?

Many of the above misconceptions would not have been enunciated and built up to an impossible crescendo if only a good summary of the SM were consulted before taking off on their avalanche. The ...
Cosmas Zachos's user avatar
11 votes

Antimuon-electron interaction

This diagram can do it, satisfying lepton number conservation at each vertex:
Martino's user avatar
  • 977
10 votes

What is (meant by) a non-compact $U(1)$ Lie group?

Generally speaking, we have$^1$ $$\text{Compact } U(1)~\cong~(e^{i\mathbb{R}}, \cdot)~\cong~S^1,$$ and $$ \text{Non-compact } U(1)~\cong~(\mathbb{R},+).$$ E.g. the covering group of the compact $U(1)$ ...
Qmechanic's user avatar
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10 votes
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Should 4 fundamental forces really be 3 because of electroweak unification?

Well, the so called "electroweak unification" is really more of an "electroweak mixing". I want to show you how the mixing is done, so that you yourself can decide whether you prefer to call it ...
Giorgio Comitini's user avatar
10 votes
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Is the discovery of the Higgs boson tantamount to discovering the Higgs mechanism?

No, the discovery of the Higgs boson has little to do with validating the Higgs mechanism, or the breathtaking role of the Higgs field Yukawa couplings giving masses to fermions. There are several &...
Cosmas Zachos's user avatar
9 votes

How to calculate the charges of W and Z bosons?

The only thing You need is the explicit form of the electric charge generator $Q$, the only one "unbroken" by the Higgs VEV: $$ Q = t_{3} + \frac{Y}{2}, $$ where $t_{3}$ is the weak isospin and $Y$ is ...
Name YYY's user avatar
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8 votes
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Why do we require gauge symmetries to commute?

Pretty much by definition. Electroweak theory is built around $SU(2) \times U(1)$, which is a Cartesian product of two groups, so it has them as commuting parts by definition. $U(1)_{\text em}$ and $U(...
Prof. Legolasov's user avatar
8 votes
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Can the weak interaction be studied without bothering the electromagnetic one?

There is no gauge theory describing the weak interaction after electroweak breaking. The meaning of symmetry breaking, after all, is that the resulting effective theory no longer has all the ...
ACuriousMind's user avatar
  • 125k
7 votes
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How were Electromagnetism and Weak interaction unified and proven?

I'm going to assume that you're nontechnical, and sketch a generalized story of why people would think that the weak interaction would have something to do with electromagnetism. This is going to be ...
Zo the Relativist's user avatar
7 votes

How many kinds of "weak charges" exist?

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 ...
rob's user avatar
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7 votes
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How it is possible to mediate a weak interactions by very heavy particle such as Boson?

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 ...
Luboš Motl's user avatar
7 votes

$SU(2)$ to $U(1)$ symmetry breaking

It is technically possible to have a theory where and $SU(2)$ symmetry spontaneously breaks to a $U(1)$ symmetry. The simplest example is when you have a field that transforms in the adjoint (spin-1) ...
Luke Pritchett's user avatar
7 votes

Why did Peter Higgs, et al. suspect that the $W$ boson(s) had mass? All the way back in 1963, '64?

Already in 1957, Julian Schwinger, Annals of Physics 2 (5) November 1957, pp 407-434, "A theory of the fundamental interactions", had inferred from the chiral structure and puny strength ...
Cosmas Zachos's user avatar
6 votes

If neutrons aren't affected by electromagnetic force, what causes it to bounce off matter?

Actually, neutrons are affected by electromagnetic forces. Specifically, by the "magnetic" part- they are electrically neutral, but have a significant magnetic dipole moment. So they are scattered by ...
6 votes
Accepted

Interpreting the Cross Section Ratio $R$

[The figure shown in the OP question above ...] is experimental data for the ratio $R = $ [...] as a function of the centre of mass energy $\sqrt{s}$ The so called cross section ratio $$R[~\sqrt{s}~] ...
user12262's user avatar
  • 4,258
6 votes

How do the right-handed fermions acquire mass?

It is not possible to fairly explain the origin of masses – and most other things – without "any mathematics" at all. Charged fermions get masses through their cubic "Yukawa" interactions with the ...
Luboš Motl's user avatar
6 votes
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What happens to the Weak Interaction after Electroweak Symmetry Breaking?

I believe you're mistakenly thinking that we have a theory (electroweak theory) that works above a 'certain scale' and then below that scale that theory goes out the window, leaving us having to ...
Rudyard's user avatar
  • 770
6 votes

What is Weak isospin in Laymans terms?

Actually, in order to understand the Isospin, the history of this notion helps. The isospin was first considered for the strong interaction, the interaction that governs the nucleus. In 1932 ...
Frederic Thomas's user avatar
6 votes

Are electroweak particles stable?

The electroweak particles are bosons of weak isospin and weak hypercharge. They can exist when the Higgs field vacuum expectation value is zero. They are massless and are stable. Our well known ...
mpv's user avatar
  • 5,220
6 votes
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Why the four gauge bosons that correspond to the $SU(2)\times U(1)$ electroweak force before symmetry breaking are not listed in the Standard Model?

They're listed under $W^+$, $W^-$, $Z$, and $\gamma$ (the photon). Those observed particles are constructed from linear combinations of $W^1$, $W^2$, $W^3$, and $B$ in the dynamical symmetry breaking ...
Sean E. Lake's user avatar
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6 votes
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Changing the hypercharge of the Higgs field

I gather you are using the (sensible!) "minority usage convention" for the Weak Hypercharge, $Q=T_3+Y$, so, then, half of what appears on this WP article table. This is the simplest and most tasteful ...
Cosmas Zachos's user avatar
6 votes

Why does the Higgs boson have electroweak charges $~T_3~$ and $~Y_w~$ but does not have an antiparticle with opposite charges?

It might be best to stare at your SM book. The Higgs field weak isospin doublet is $$ H = \begin{pmatrix} \phi^+ \\ \phi^0 \end{pmatrix}\equiv \frac{1}{\sqrt 2} \begin{pmatrix} \varphi_1-i\varphi_2 \\...
Cosmas Zachos's user avatar
6 votes
Accepted

Why are electric monopoles not interpreted as topological defects but magnetic monopoles are?

Recall that electric-magnetic duality involves an $S$-transformation, namely the coupling constant undergoes $e\leftrightarrow 1/e$. This constant is very different from $1$ (in particular, $e\ll1$), ...
AccidentalFourierTransform's user avatar
6 votes
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A Doubt on Covariant Derivatives and Particle Physics

This is part of the Higgs mechanism. The EM photon field $A_{\mu}$ is identified as a linear combination of the $W^3_{\mu}$ and $B_{\mu}$ fields that remains massless after the electroweak symmetry ...
Qmechanic's user avatar
  • 203k
6 votes

Why does beta decay of a free neutron not violate conservation of energy?

The W-boson is virtual, in the sense that it pops out of the vacuum as needed on borrowed funds, makes its brief cameo appearance to fulfill its weak-interaction job description, and then pays back ...
niels nielsen's user avatar

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