All Questions
Tagged with standard-model symmetry-breaking
105
questions
3
votes
0
answers
70
views
Parity violation via symmetry breaking?
(Apologies in advance for a poorly formulated question.) In Physics, if something can be equally well found in state A or state B, but for whatever reason is in state A, we sometimes observe the ...
- 2,921
0
votes
1
answer
103
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Custodial symmetry of the standard model symmetry group $SU(2)_L \times SU(2)_R$
I am studying the standard model including the Higgs sector and electroweak interactions. Here, all of my terms have their usual meanings. Therefore my symmetry group is $SU(2)_L \times SU(2)_R \times ...
- 51
0
votes
1
answer
56
views
Why don't we include diagrams with fermion and gauge boson external lines while calculating the effective potential of Standard model?
While calculating the effective potential of Higgs boson, we aim at $V_{eff}(h)$ instead of $V_{eff}(h, W^{+}, W^{-}, Z, quarks, leptons)$. I think the true vacuum should be the minimum of this ...
- 619
1
vote
2
answers
163
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Before spontaneous symmetry breaking, what is the difference between the fermion generations?
Before spontaneous symmetry breaking (SSB), all fermions have the same mass (0). Across the 3 different fermion generations, all the (left) quarks doublets have the same weak isospin, and all the up ...
- 454
0
votes
1
answer
58
views
Is the weak quark mixing a consequence of electroweak symmetry breaking?
Because of the CKM matrix, the quark doublets that are changed by $W^{+}$ and $W^{-}$ include a linear combination of quark flavours, instead of the pure quark flavours. I was wondering if, before ...
- 454
0
votes
0
answers
72
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Are all of the characteristics of elementary particles essentially symmetry differences?
I am trying to get a better conceptual grasp on the "splitting" of the fundamental forces at the beginning of the universe.
The first force to separate was the gravitational force. Am I ...
- 325
-2
votes
1
answer
107
views
Why do the members of $SU(2)$ doublets gain different masses after spontaneous symmetry breaking?
Before spontaneous symmetry breaking (SSB) elementary particles belonging to the same $SU(2)$ doublets are indistinguishable, which clearly is not the case after SSB.
I am comfortable with the idea of ...
- 454
3
votes
2
answers
161
views
How do we known that $\langle \bar{\psi}_i \psi_j\rangle=(250 MeV)^3\delta_{ij}$?
I have started to read the phenomenology of QCD in low energy regime. I understand that, from the QCD renormalization group equation, the QCD becomes nonperturbative theory when energy scale is below $...
- 31
0
votes
1
answer
96
views
$C$-violation in SM Lagrangian?
It's usually said that SM Lagrangian violates charge conjugation, and should be obvious from the fact that "only left handed fermions are charged under $SU(2)_{L}$ but left and right handed ...
- 475
1
vote
1
answer
133
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QFT symmetry breaking and CP violation
Since the weak interaction violates CP symmetry but electromagnetism doesnt,does it mean that the electroweak fields also violates CP symmetry?Can a field which violates some symmetry be the product ...
2
votes
0
answers
62
views
Predicting a nonzero mass for the photon
This is a concern I had after I had read the reply for a previous question I had: On the masslessness of the photon
So, I have been told that there are cases in which the gauge symmetry that preserves ...
- 3,992
2
votes
0
answers
129
views
What is the current theoretical and experimental understanding of the mass of the photon? [duplicate]
To what extend are we allowed to claim that the photon has some sort of mass, below some threshold. We certainly have no experimental evidence that the photon is completely massless, but, due to the ...
- 3,992
4
votes
1
answer
176
views
Why is gluon massless from GUT point of view?
For not violating the gauge invarinace, of course, the gluon is massless. In respect of Spontaneous Symmetry breaking(SSB), however, I wonder why the gluon is massless, compared the $W^+$, $W^-$, $Z$ ...
- 108
1
vote
1
answer
70
views
Explicit computation in finding the minima of a gauge symmetry invariant potential
I'm reading some notes about the symmetry breaking and the standard model. From what I understand, typically one has a symmetry group of transformations (the gauge group) acting on vectors of fields, ...
- 23
4
votes
1
answer
302
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Global symmetries QCD goldstone bosons
Beside the local $SU(3)$-Color-symmetrie The QCD Lagrangian also has global symmetries:
$$L_{QCD}=\sum_{f,c}\bar{q_{fc}}(i\gamma^\mu D_\mu - m ) q_{fc} - \frac{1}{4}F^a_{\mu \nu} F^{a \mu \nu} $$
$SU(...
- 63