Restoring universality

In models of weak and electromagnetic interactions with six or more quarks, universality and, in some cases, the V-A structure of leptonic and semi-leptonic interactions have to be put in by hand. We show how both properties remerge naturally if replacing the usual SU(2) weak isospin group by a large SU(4) group, which also lends itself quite naturally to grand unifications (including strong interactions). The model needs eight quarks and two charged heavy leptons, and features, nesides universality and V-A, non-equality of neutral current scattering of ν's on leptons and on hadrons, and very reasonable relations for (bare) fermion masses.     

Leptons with high weak isospin and compositeness

Heavy leptons with high weak isospin, predicted in a subcomponent model of quarks and leptons with SU(2)_L × U(1) symmetry, are examined phenomenologically in connection with recently reported anomalous events and super high energy physics. In constructing the effective lagrangian based on the subcomponent structure, I_W = 1 heavy leptons play a special role in the effective interaction.     

Bounds on radii and anomalous magnetic dipole moments of quarks and leptons from LEP,SLC and HERA

Leptons, quarks and gauge bosons are assumed to be pointlike particles in the Standard Model. Stringent bounds on the radii of quarks and leptons and their weak anomalous magnetic moments can be derived from the high-precision measurements at LEP and SLC. We find a model-independent bound ofR?10^?17 cm for quark and lepton radii. HERA will provide complementary information on the electromagnetic static properties of the quarks and the parameters of the charged quark currents.     

Consequences of flavor as a dynamical quantum number

Phenomenological consequences of composite leptons and quarks are studied in the class of models in which the fermions of the first generation (i.e. e, ν_e, u and d) are the ground states of (unspecified) composite systems and each new generation is a radial excitation level. We find that the standard QED results remain practically unaffected in such a scheme. The excited quarks/leptons having mass larger than 5 GeV could be produced in e⁺e^- experiments and would increase the value of R by several per cent as compared with the case of the pointlike quarks and leptons. An argument is given for the smallness of the anomalous magnetic moments of composite leptons.     

Selection rules in a unified gauge model of leptons and hadrons

Decay modes and lifetimes of quarks, vector mesons and protons are determined for the unified model of leptons and hadrons recently proposed by Pati and Salam. It is found that while both the quarks and gauge mesons decay too rapidly to be observed, protons will be comfortably stable against decay into leptons, consistent with earlier estimates and existing experimental evidence. It is of special interest that while quarks may not be directly observable, their presence may be verified owing to the uniqueness of their preferred decay into quite a large number of pions. We also discuss an anomalous lepton-hadron scattering process whose occurrence would imply the presence of exotic SU(4) gluons carrying both baryon and lepton number.     

Anomalous moments of heavy charged leptons

If leptons and quarks are composite particles we expect them to have anomalous moments: an anomalous magnetic moment and an analogue of this with respect to the weak neutral current. If these moments are suppressed by chiral symmetry they will have sizeable values only for heavy fermions, e.g. for fermions of the fourth generation. The forward-backward asymmetry of e⁺e⁻ → f̄f on the Z⁰ resonance is particularly suited for detecting the anomalous “weak magnetic” moment of f if f is the charged lepton of the fourth generation. Under favourable circumstances this moment may lead to a 10% effect.     

THE COMPOSITE MODEL OF LEPTON AND QUARK WITH ONLY ONE CONSTITUENT SCALAR

We propose a composite model of leptons and quarks containing two constituent fermions of spin 1/2 and a constituent scalar. The constituent fermions are massless and color singlets. Leptons, quarks and weak vector bosons are composites confined by SU(3)_H local gauge interaction, where leptons are made of three constituent fermions and quarks are two-body composites of a scalar and a fermion. The number of the constituent particles is less in our model. There are less exotic leptons and quarks. Quark-lepton parallelism holds. Weak interactions appear only at the composite level as residual short-range interactions among hypercolor singlets. The violation of parity occurs by the mechanism of dynamical symmetry breaking.     

Generations of massless composite quarks and leptons

We present a QCD-like composite model in which quarks, leptons and technifermions are three-body systems made out of three kinds of massless elementary fermions t, c and w, each carrying technicolor, color and weak gauge interactions, respectively. Discrete symmetries, remnants of the U(1)_A of the original lagrangian, are responsible for the masslessness of all the quarks and leptons and give the precise meaning of the generations. The model exhibits three generations for both quarks and leptons. Small but non-zero masses of the quarks and leptons are produced by the technicolor condensate of the composite technifermions, which thereby leads to the non-trivial Cabibbo mixing. Proton decays are all forbidden at the mass scale of the QCD-like theory.     

Weak interaction of quarks

A theory of weak interaction of quarks is developed in the framework of SU (2) symmetry. Expressions are obtained for the probability of decay of quarks into leptoquarks, quarks into leptons, and leptoquarks into leptons. A model is also constructed of the interaction of quarks with matter in which strong and electromagnetic interactions of quarks with matter are forbidden. In this model, the weak interaction of quarks is the main form of interaction between quarks and matter. In this connection, it is suggested that quarks should be looked for in nature in the products of their weak decay in accordance with the theory developed here.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 30–36, July, 1974.     

Azimuthal angular dependence of decay lepton in e^+ e^- \to t \bar{t}

We discuss top quark production and its subsequent decay as used for searching new physics at lepton colliders. The angular dependence of the decay leptons is calculated including both QCD corrections and anomalous couplings. The off-diagonal spin basis for the top and anti-top quarks is shown to be useful to probe the anomalous couplings. Received: 11 August 2000 / Published online: 27 November 2000     

Parity violating neutral currents in a left-right symmetric gauge model

We consider parity violating effects in the neutral sector of a left-right symmetric SU(2)_L × SU(2)_R × U(1) gauge model of weak and electromagnetic interaction. With four quarks and four leptons, the parity violating optical rotation in atoms is estimated to be about an order of magnitude smaller (and of opposite sign) compared to the Salam-Weinberg (SW) model prediction. However, with new quarks and leptons this effect can be arranged to be even smaller. Weak-electromagnetic interference effects are quantitatively different from those found in the SW model. A unified gauge theory which embeds the left-right symmetric gauge model is briefly discussed.     

Quark imprisonment as the origin of strong interactions

We propose a formal scheme in which the only dynamical ingredients are weak and electro-magnetic interactions with quarks and leptons treated on the same footing. Strong interactions are generated by the requirement that quarks do not appear physically.     

Relations between the masses of the superpartners of leptons and quarks,the goldstino coupling and the neutral currents

The mass² splittings between leptons and quarks and their spin-0 partners under supersymmetry are related to the goldstino couplings. The bosonic partner of the goldstino cannot be the photon itself. But it should be, in part, a linear combination of the various neutral gauge bosons. As a result, mass relations constrain the neutral current structure of the theory. They require the existence of at least two neutral gauge bosons in addition to the photon and suggest the possibility of a universal mass² splitting between leptons and quarks and their spin-0 partners.     

SU(4) weak currents

We suggest SU_L(4) ? U(1) as the gauge symmetry of weak and electromagnetic interactions for quartets of quarks and leptons. We analyze how the (additional) SU_L(4) weak currents (besides the SU_L(2) subgroup) could affect the weak interactions of ordinary particles, the atomic parity violation, the neutral-current neutrino reactions and the decays of the τ heavy lepton and the charmed mesons. The suppression of neutral-current parity violation in atomic experiments can be naturally incorporated in this model while at the same time the success of the Weinberg-Salam model with respect to the inclusive neutral current data is kept. The model has limited freedom and therefore many definite predictions.     

Lepton number conserving and non-conserving weak interactions

A gauge theory of weak and electromagnetic interactions based on a group containing the SU(4) group of unitary unimodular transformations on the lepton and quark quartets, is shown to be possible only if lepton and/or baryon number are not exactly conserved, or if there exist particles that cannot be built of quarks and leptons. The spontaneous breakdown of lepton number conservation in terms of tadpole-producing spinless leptons is considered.     

Vectorlike weak currents and new elementary fermions

Recent experimental discoveries encourage speculation that there may be more than four “flavors” of tricolored quarks and/or new flavors of leptons. A vectorlike gauge theory of the weak, electromagnetic, and associated neutral current interactions is then an attractive possibility. We present as an illustrative example a minimal theory based on six quark flavors and six lepton flavors and on the group SU₂ × U₁ (presumably a subgroup of a larger gauge group).     

A DISCUSSION OF ANOMALOUS MAGNETIC MOMENT OF QUARKS AND LEPTONS IN A SUBSTRUCTURE MODEL

In this paper we present a discussion on anomalous magnetic moment of a massive fermion and leptons in a substructure model, in which quarks and leptons are composed of a massive fermion and a massive scalar boson. we have obtained some limitations on their masses and charges.     

Weak interactions as manifestations of the substructure of leptons and quarks

A new model for the substructure of leptons, quarks and weak bosons is investigated. The weak interactions are residual effects due to the substructure. No spontaneous symmetry breaking is needed to generate masses. The structure of the weak interactions at high energies is expected to deviate substantially from the one predicted by the standard SU(2) × U(1) theory.