Minimal subconstituent models of quarks and leptons (original) (raw)

The extended chiral quark model confronts QCD

Nuclear Physics B - Proceedings Supplements, 2000

We discuss the truncation of low energy effective action of QCD below the chiral symmetry breaking (CSB) scale, including all operators of dimensionality less or equal to 6 which can be built with quark and chiral fields. We perform its bosonization in the scalar, pseudoscalar, vector and axial-vector channels in the large-N c and leading-log approximation. Constraints on the coefficients of the effective lagrangian are derived from the requirement of Chiral Symmetry Restoration (CSR) at energies above the CSB scale in the scalar-pseudoscalar and vector-axial-vector channels, from matching to QCD at intermediate scales, and by fitting some hadronic observables. In this truncation two types of pseudoscalar states (massless pions and massive Π-mesons), as well as a scalar, vector and axial-vector one arise as a consequence of dynamical chiral symmetry breaking. Their masses and coupling constants as well as a number of chiral structural constants are derived. A reasonable fit of all parameters supports a relatively heavy scalar meson (quarkonium) with the mass ∼ 1 GeV and a small value of axial pion-quark coupling constant g A ≃ 0.55.

Composite quarks and leptons in higher space-time dimensions

Physical Review D, 2002

A new approach towards the composite structure of quarks and leptons in the context of the higher dimensional unified theories is proposed. Because of certain strong dynamics much like ordinary QCD, every possible vectorlike set of composites appears in higher dimensional bulk space-time. However, through a proper Sherk-Schwarz compactification only chiral multiplets of composite quarks and leptons survive as the massless states in four dimensions. In this scenario restrictions related to 't Hooft's anomaly matching condition turn out to be avoided and, as a result, the composite models look rather simple and economical. We demonstrate our approach by an explicit construction of a model of preons and their composites unified in the supersymmetric SU(5) GUT in five space-time dimensions. The model predicts precisely three families of composite quarks and leptons being the triplets of the chiral horizontal symmetry SU h which automatically appears in the composite spectrum when going to ordinary four dimensions.

A Model of Lepton and Quark Structure

Physica Scripta, 1980

We propose a model of particles with two very massive fundamental constituents, maxons. One of them is a fractionally charged color triplet and the other is neutral color singlet. Leptons, quarks and the weak bosons are quasiparticles in the system of interacting maxons. Some implications of the model are discussed. This is a typo corrected manuscript reconstruction (

Chiral symmetry breaking and the quark model

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.

Chiral symmetry: Pion-nucleon interactions in constituent quark models

Physical Review C, 1997

We study the interactions of an elementary pion with a nucleon made of constituent quarks and show that the enforcement of chiral symmetry requires the use of a two-body operator, whose form does not depend on the choice of the pion-quark coupling. The coordinate space NN effective potential in the pion exchange channel is given as a sum of terms involving two gradients, that operate on both the usual Yukawa function and the confining potential. We also consider an application to the case of quarks bound by a harmonic potential and show that corrections due to the symmetry are important.

A chiral model for qq and qqqq mesons

We point out that the spectrum of pseudoscalar and scalar mesons exhibits a cuasi-degenerate chiral nonet in the energy region around 1.4 GeV whose scalar component has a slightly inverted spectrum. Based on the empirical linear rising of the mass of a hadron with the number of constituent quarks which yields a mass around 1.4 GeV for tetraquarks, we conjecture that this cuasi-chiral nonet arises from the mixing of a chiral nonet composed of tetraquarks with conventional qq states. We explore this possibility in the framework of a chiral model assuming a tetraquark chiral nonet around 1.4 GeV with chiral symmetry realized directly. We stress that UA(1) transformations can distinguish qq from tetraquark states, although it cannot distinguish specific dynamics in the later case. We find that the measured spectrum is consistent with this picture. In general, pseudoscalar states arise as mainly qq states but scalar states turn out to be strong admixtures of qq and tetraquark states. We work out also the model predictions for the most relevant couplings and calculate explicitly the strong decays of the a0(1450) and K * 0 (1430) mesons. From the comparison of some of the predicted couplings with the experimental ones we conclude that observable for the isovector and isospinor sectors are consistently described within the model. The proper description of couplings in the isoscalar sectors would require the introduction of glueball fields which is an important missing piece in the present model.

Chiral model for q¯q and qq¯qq mesons

Physical Review D, 2004

The structure of weak interactions for composite quarks and leptons

Nuclear Physics B, 1984

We consider a model of quarks and leptons as quasi-Goldstone fermions which is based on an underlying supersymmetric SU(2)uc x SU(2)',, preon theory. The spontaneous breakdown of a global U(6) X U(6)' X U(1) symmetry to U(4) X U(4)' X SU(2),,, creates both quarks and leptons and at the same time allows for the possibility of having either residual or fundamental weak interactions. Effective lagrangians in the confining phase of the theory are compared to those emerging from a complementary picture and the problems connected with the nature of the weak interactions are discussed in this context also.

Composite-component duality and baryonic number in subcomponent models for quarks and leptons

Physics Letters B, 1981

Composite-component duality appears to be the characteristic feature to assure approximate proton stability within a vast class of subcomponent models for quarks and leptons. We discuss six models which allow for the observed quarklepton spectrum: two models have two color triplets and two singlets as subcomponents, bound by a subcolor SU(7) or SU( ); two models have a color triplet, an antitriplet and two singlets, and again subcolor SU(7) or SIJ(9); two models have two triplets, two antitriplets and four singlets, and subcolor O(15) or O(17).