Quark-lepton Research Articles

Neutral-current constraints on SU(2) ⊗ U(1) gauge theories

In this paper we formulate a set of empirical rules for constructing SU(2) \ensuremath{\bigotimes} U(1) gauge models by considering the constraints imposed by the present neutral-current data. To do this we allow, apart from the constraints imposed by universality and quark-lepton symmetry, arbitrary left- and right-handed fermion multiplet structures as well as an arbitrary Higgs sector. Before doing the general analysis we consider two examples where there are additional simplifying results. Some simple models satisfying the empirical rules are also discussed.

Gauge models of theVV+AAtype and their effective neutrino interactions

We display, and compare with neutrino data, all possible gauge models with exactly two diagonal Z bosons, such that the neutral-current interaction of the usual quarks and leptons is of the form VV + AA, thereby conserving parity in atomic physics. Only three solutions are found to be consistent with data. One is the ''left-right'' or ''ambidexterous'' SU(2)/sub L/ x SU(2)/sub R/ x U(1) model which reduces to the standard SU(2) x U(1) model; the other two are based on SU(3) x U(1) and one of them reduces to an SU(2) x U(1) model with a (u,b)/sub R/ doublet. These latter solutions are only obtainable by abandoning the usual quark-lepton symmetry that was assumed by one of us in an earlier paper.

Gauge theories of weak interactions with left-right symmetry and the structure of neutral currents

Failure to detect parity-violating effects in atomic transitions by Oxford and Washington groups would appear to rule out the Weinberg-Salam $\mathrm{SU}(2)\ensuremath{\bigotimes}\mathrm{U}(1)$ model as well as any variation of it that respects natural conservation laws for charm and strangeness to order $\ensuremath{\alpha}$ ${G}_{F}$ (called "natural") and obeys quark-lepton symmetry. In this paper, a simple left-right-symmetric model based on the ${\mathrm{SU}(2)}_{L}\ensuremath{\bigotimes}{\mathrm{SU}(2)}_{R}\ensuremath{\bigotimes}\mathrm{U}(1)$ group with four and six quark flavors is analyzed and found to accomodate the results of the atomic experiments as well as the other features of neutral-current phenomena.

Implications for Gauge Theories if Search for Parity Nonconservation in Atomic Physics Fails

Failure to detect parity-nonconserving effects in atomic transitions coupled with the available neutrino neutral-current data would appear to rule out all SU(2) \ensuremath{\bigotimes} U(1) gauge theories which respect "natural" conservation laws for charm and strangeness and quark-lepton symmetry. We analyze a left-right symmetric "natural" (in the above sense) and quark-lepton symmetric $\mathrm{SU}{(2)}_{L}\ensuremath{\bigotimes}\mathrm{SU}{(2)}_{R}\ensuremath{\bigotimes}\mathrm{U}(1)$ gauge theory and find that it accommodates all the features of neutral-current phenomena.

Testing quark-lepton symmetry in e+e- annihilation

Testing quark-lepton symmetry in e+e- annihilation

Nonconservation of muon number and CP noninvariance

Based upon a possible quark-lepton symmetry, we suggest that the conservation of muon number may be violated by a matrix element of the order of the Fermi constant times the CP-violating parameter times the squared electric charge. We urge a renewed experimental search for the decay μ ± → e ±e +e − with a branching ratio of about 4 × 10 −9.

Symmetries of Neutral Weak Currents

The U2 × U2 and D symmetries of the leptonic weak interaction are extended, within the framework of the quartet–quark model, so as to include the hadronic weak interaction. The total weak current satisfies a lepton–quark symmetry. Application of these symmetries to the neutral current weak interaction restricts the current to be composed only of vector and axial vector pieces, and also restricts the symmetry properties of its (V−A) part. Experimental implications of these symmetries in various neutrino reactions are investigated. There are some ambiguities as regards the (V+A) part of the neutral current, which may, however, be resolved soon if more experimental data become available.

Sea level search for leptonic quarks in cosmic rays

A search has been made for relativistic leptonic quarks (chargese/3 and 2e/3) in the cosmic radiation near sea level using a narrow-angle scintillation counter telescope. The apparatus was oriented at large zenith angles (>75°) and thus used the atmosphere as an extended filter for hadronic quarks. A null result was obtained, leading to upper limits on such quark intensities of ∼1.7·10−8 cm−2 sr−1 s−1 at the 90% confidence level.

An underground search for leptonic quarks in the cosmic radiation

The flux of relativistic leptonic particles with charges ±e/3, ±2e/3, ±4e/3 in cosmic rays underground at 63 m w.e. was measured using a six-scintillation-counter telescope. The following upper limits were established: φ(±e/3)≤1.8·10−10 cm−2sr−1s−1, (90% confidence) φ(±2e/3)≤1.8·10−10 cm−2sr−1s−1, (90% confidence) φ(±4e/3)≤(1.1±1.8)·10−8 cm−2 sr−1 s−1, at threshold energies of (2.1±0.1) GeV, (8.5±0.6) GeV, (22±1) GeV respectively.

Search for leptonic quarks in the mass range 100 to 900 MeV

A search has been performed for photoproduced leptonic particles with fractional charges (leptonic quarks). With a 99% statistical significance, none have been found with charges 1 3 and 2 3 and masses below 850 and 900 MeV.

A search for leptonic quarks

A search for leptonic quarks (non-strongly interacting fractionally charged particles) was performed at the Cambridge electron accelerator. No fractionally charged particles were detected. The following limits on the quark mass were calculated assuming that the Bethe-Heitler pair production cross section describes the production process. Charge (z Q ) = 1 3 : M Q ⩾ 780 MeV or M Q ⩾ 0.5 MeV. 2 3 : M Q ⩾ 840 MeV or M Q ⩾ 2.0 MeV .