Universality of spontaneous chiral symmetry breaking in gauge theories (original) (raw)
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A mechanism for instanton induced chiral symmetry breaking in an extended QCD model (QCD with fundamental scalars) is proposed to describe quarks and gluons inside a baryon. The model Lagrangian that we use has the same symmetry properties as QCD. The scalar fields are shown to develop vacuum expectation values in the instanton background and generate masses for the three generation of quarks. The minimization condition is also used to break the flavour symmetry to make the s-quark heavier that the u and d quarks.
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Nuclear and Particle Physics Proceedings, 2016
The phenomenon of dynamical quark mass generation is studied in QCD within the framework of a gauge invariant formalism. An exact relationship is established between the equation satisfied by the scalar part of the two-point gauge invariant quark Green's function and the quark-antiquark bound state equation in the chiral limit. A possible nontrivial solution of the former yields a massless pseudoscalar solution of the bound state equation with vanishing total momentum. The result is also corroborated by the corresponding Ward-Takahashi identity. The problem is explicitly solved in two-dimensional QCD in the large-N c limit.
Chiral polarization scale of QCD vacuum and spontaneous chiral symmetry breaking
Journal of Physics: Conference Series, 2013
It has recently been found that dynamics of pure glue QCD supports the low energy band of Dirac modes with local chiral properties qualitatively different from that of a bulk: while bulk modes suppress chirality relative to statistical independence between left and right, the band modes enhance it. The width of such chirally polarized zonechiral polarization scale Λ ch-has been shown to be finite in the continuum limit at fixed physical volume. Here we present evidence that Λ ch remains non-zero also in the infinite volume, and is therefore a dynamical scale in the theory. Our experiments in N f =2+1 QCD support the proposition that the same holds in the massless limit, connecting Λ ch to spontaneous chiral symmetry breaking. In addition, our results suggest that thermal agitation in quenched QCD destroys both chiral polarization and condensation of Dirac modes at the same temperature T ch > Tc.
U a (1) Symmetry Breaking and the Scalar Sector of QCD
International Journal of Modern Physics A, 2001
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Annals of Physics, 2012
We study chiral symmetry breaking in QCD-like gauge theories introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamical gauge boson mass generation. The effective confining propagator has the form 1/(k 2 + m 2) 2 and we study the bifurcation equation finding limits on the parameter m below which a satisfactory fermion mass solution is generated. Considering the evidences that the coupling constant and the gauge boson propagator are damped in the infrared, due to the presence of dynamically massive gauge bosons, the major part of the chiral breaking is mostly due to the confining propagator. We study the asymptotic behavior of the gap equation containing confinement and massive gauge boson exchange, and find that the symmetry breaking can be approximated at some extent by an effective four-fermion interaction generated by the confining propagator. We compute some QCD chiral parameters as a function of m, finding values compatible with the experimental data. Within this approach we expect that lattice simulations should not see large differences between the confinement and chiral symmetry breaking scales independent of the fermionic representation and we find a simple approximate relation between the fermion condensate and dynamical mass for a given representation as a function of the parameters appearing in the effective confining propagator.