All Questions
Tagged with quantum-chromodynamics symmetry-breaking
43
questions
1
vote
0
answers
410
views
How to find the explicit value of the fermion vacuum expectation value?
In the derivation for Goldstone modes, a pdf I found online (scipp.ucsc.edu/~dine/ph222/goldstone_lecture.pdf) says it's believed the above-mentioned expectation value $\langle \bar{ \psi} \psi \...
- 737
3
votes
1
answer
483
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Relevance of the condensate $\langle 0 | \bar q q | 0 \rangle$ to SSB of chiral QCD symmetry
The QCD lagrangian with two massless flavours of quarks takes the form $$\mathcal L = \sum_{i=u,d} i \bar q_i \gamma_{\mu} D^{\mu} q_i.$$ Defining operators to project out the left and right handed ...
- 3,569
14
votes
1
answer
3k
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Physical meaning of the chiral condensate in QCD
Considering the QCD Lagrangian in the chiral limit, where all the quarks masses are set to zero. Then the Lagrangian has the following chiral symmetry:
$$
SU(L)_{V} \times SU(L)_{A} \times U(1)_{V} \...
- 141
2
votes
1
answer
239
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Chiral current VEV below the QCD scale
Let's have pure QCD. I know that after spontaneous symmetry breaking quark bilinear form are replaced by their averaged values:
$$
\bar{q}_{i}q_{j} \to \langle \bar{q}_{i}q_{j}\rangle \approx \Lambda_{...
- 8,901
9
votes
1
answer
807
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Spontaneous symmetry breaking of anomalous global abelian symmetries and $U(1)$ of QCD
Let me restate the $U(1)$ problem of QCD:
Let us forget about the $s$ quark, and consider the $u$ and $d$ massless. This is
a good approximation since $m_{u,d} \ll \Lambda_{QCD}$. Then $\mathscr{...
- 498
7
votes
1
answer
479
views
Massive Gauge Bosons without Higgs fields
In a possible theory like our Standard model but without a Higgs i.e.:
$$ \mathcal{L}=i\bar{\Psi}_f\gamma_\mu D^\mu\Psi_f-\text{Tr}[G^b_{\mu\nu}G^{b\,\mu\nu}] $$
where $b,f$ run over the typical ...
- 823
1
vote
1
answer
149
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Interpretation of vector mesons in QCD
It is well-known that scalar mesons are interpreted as pseudogoldstone bosons which is connected with spontaneous broken $SU(3) \times SU(3)$ symmetry to $SU(3) \times SU(3) / SU(3)_{chiral}$.
Is ...
- 6,564
11
votes
1
answer
528
views
From which dimensionful constants does proton mass arise?
It is well known that the most of the proton (or any other hadron with light quarks) mass is not made up from quark masses, but it is dynamically generated by QCD mess inside. I've also heard that, ...
- 305
5
votes
2
answers
1k
views
Origin of quark masses
Does all the mass of the quarks in the standard model come from the Higgs sector or is there also a contribution to quark masses due to QCD chiral symmetry breaking?
- 26.8k
3
votes
1
answer
1k
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Dilaton field and Scale symmetry breaking
I have read at some places that a dilaton field is associated with the spontaneous breaking of scale symmetry in a theory. (While others would be difficult to trace right now, the most easily ...
- 405
8
votes
1
answer
361
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Intuitive explanation of how hadron mass emerges from the strong force
I'm not familiar with QCD, but I'm looking for intuitive explanation of this phenomenon (it could be that easy explanation does not exist).
What I've read is that large part of hadron masses arises ...
- 421
11
votes
1
answer
470
views
What's the heuristic reasoning for Chiral Symmetry breaking
In Peskin and Schroeder (page 669), and other references, the heuristic reasoning for why one would expect chiral symmetry breaking at low energies is that quark masses are small and hence it's not ...
- 3,492
2
votes
3
answers
886
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The status of $SU(3)_C$ symmetry in the Standard Model
In the Standard Model of Particle physics the $SU(2)_{EW}$ symmetry and the $SU(2)$ isospin symmetry are broken. What about $SU(3)_C$? Is it broken too?
if YES, what breaks the symmetry?
If NO, what ...
- 2,335