The extended chiral quark model confronts QCD

2012

In this thesis, we focus on some aspects concerning hadronic phenomena at low energy, below 1 GeV, under which the spontaneous breaking of chiral symmetry takes place. Under this scale, the spectrum of Quantum Chromodynamics reduces to an octet of light pseudo-scalar mesons (π, K and η). But because of the confinement property, QCD under 1 GeV is highly non-perturbative, it is thus not possible to describe at low energy the dynamics of these mesons in terms of gluons and quarks (in that case the three light quarks u,d, and s). Two main alternatives exist to circumvent this major obstacle: Lattice QCD and Effective Field Theories. Lattice QCD is concerned with the numerical computations of various hadronic observables, while Effective Field Theories correspond to analytical frameworks adapted to a particular energy scale. In the case of QCD at low energy, this role is devoted to Chiral Perturbation Theory (ChiPT). This theory can be built either from two quark flavours (u and d), or ...

Nuclear Physics B, 1977

We review the subject of chiral sytmnetry breaking and its connection with the quark model. When the light plane SU(3) charges and quark field density matrix elements are transformed back to the usual static basis it becomes clear that expectation values of chiral breaking operators, such as qXiq, do not necessarily have simple SU(3) transformation properties. Starting with the standard current quark chiral Hamiltonian H' = rnuKU + mddd + ruffs, we then use current quark light-cone distribution function concepts in combination with constraints from (i) Compton amplitude fixed poles, (ii) baryon octet and decuplet mass differences, (iii) ~rN and KN a terms, (iv) GA/GV, (v) lowenergy ~r photoproduction multipoles, (vi) Goldberger-Treiman discrepancies, (vii) meson mass ratios in PCAC and, (viii) meson mass differences to determine in = ½(m u + rod) and m s in more than four independent ways. Our results are all mutually consistent and yield the values ~z ~ mrr and ms/~Z ~ 5. In particular the independent baryon and meson sectors of the theory are completely compatible.

Arxiv preprint hep-ph/0601196, 2006

2011

A low energy effective field theory model for QCD with a scalar color octet field is discussed. The model relates the gluon mass, the constituent quark masses and the quark condensate. The gluon mass comes about √ N c Λ QCD with the quark condensate being proportional to the gluon mass squared. The model suggests that the restoration of chiral symmetry and the deconfinement transition occur at the same temperature and that, near the transition, the critical exponent for the condensate is twice the gluon mass one. The model also favors the decoupling like solution for the gluon propagator.

Physics Letters B, 1976

Baryon chiral symmetry quark model parameters are linked together in a consistent manner leading to mp~ mn~ 140 MeV, mh ~ 670 MeV and c = eS/eo ~ -0.8. This includes consideration of baryon octet and decuplet mass splittings, the proton Compton scattering fixed pole, baryon a terms, and nucleon photoproduction of pions along with a sume rule for gA.

International Journal of Modern Physics A, 1997

We derive the dimensional nonperturbative part of the QCD effective action for scalar and pseudoscalar meson fields by means of chiral and conformal bosonization. The related structural coupling constants L5 and L8 of the chiral Lagrangian are estimated using general relations which are valid in a variety of chiral bosonization models without explicit reference to model parameters. The asymptotics for large scalar fields in QCD is elaborated, and model-independent constraints on dimensional coupling constants of the effective meson Lagrangian are evaluated. We determine also the interaction between scalar quarkonium and the gluon density and obtain the scalar glueball-quarkonium potential.

Physical Review D, 1996

Journal of Mathematical Sciences, 2000

We compare two QCD-inspired quark models with four-fermion interaction, without and with the remnant coupling to low-energy gluons, in the regime of dynamical chiral symmetry breaking (DCSB). The first one, the Nambu-Jona-Lasinio (NJL) model ensures the factorization of scalar and pseudoscalar meson poles in correlators, the well-known Nambu relation between the scalar meson mass and the dynamical quark mass, m σ = 2m dyn , and the residual chiral symmetry in coupling constants characteristic for the linear σ-model. The second one, the Gauged NJL model, happens to be qualitatively different from the NJL model, namely, the Nambu relation is not valid and the factorization of light meson poles does not entail the residual chiral symmetry, i.e. it does not result in a linear σ-model. The more complicated DCSB pattern in the GNJL model is fully explained in terms of excited meson states with the same quantum numbers. The asymptotic restrictions on parameters of scalar and pseudoscalar meson states are derived from the requirement of chiral symmetry restoration at high energies.

Nuclear Physics A, 2001

We establish a relationship between the scalar-meson spectrum and the U A (1) symmetry-breaking 't Hooft interaction on one hand and the constituent-quark flavor singlet axial coupling constant g (0) A,Q on the other, using an effective chiral quark field theory. This analysis leads to the new sum rule g

Physical Review D, 2013

Exploiting the recent lattice results for the infrared gluon propagator with light dynamical quarks, we solve the gap equation for the quark propagator. We thus model the chiral symmetry breaking mechanism with increasing number of flavours and study confinement (intimately tied with the analytic properties of QCD Schwinger functions) order parameters. We obtain, with this approach, clear signals of chiral symmetry restoration and deconfinement when the number of light quark flavors exceeds a critical value of N c f ≈ 8 ± 1, in agreement with the state-of-the-art direct lattice analysis of chiral symmetry restoration in QCD.