All Questions
5
questions
9
votes
2
answers
796
views
How is the pion related to spontaneous symmetry breaking in QCD?
In chapter 19 of An Introduction to Quantum Field Theory by Peskin & Schroeder, they discuss spontaneous symmetry breaking (SSB) at low energies in massless (or nearly massless) QCD, given by
$$\...
- 101
3
votes
0
answers
360
views
Pion mass in theta vacuum
Does the mass of the charged pion depend on the QCD vacuum angle? I've seen it said---e.g., in these TASI lectures---that when the quark mass matrix is real and there is a nonzero QCD vacuum angle $\...
- 61
4
votes
1
answer
2k
views
Question about the linear sigma-model
Suppose the linear sigma-model lagrangian:
$$
L = \bar{N}(i\gamma_{\mu}\partial^{\mu}-g_A \phi)N + |\partial_{\mu}\phi|^{2} - V(|\phi|) - c\sigma ,
$$
where
$$
N = \begin{pmatrix} p \\ n\end{pmatrix}, ...
- 8,901
14
votes
1
answer
3k
views
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
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