Search

We show that the low energy effective model derived from SU ( 5 ) with 45-plet Higgs can account for the recently reported enhanced diphoton decay rate of the Standard Model (SM)-like Higgs with mass about 125 GeV . This model extends the SM by an extra Higgs doublet and color-octet scalar doublet. We show that the charged octet scalars are not severely constrained by flavor changing neutral current and can be light. However, the K 0 – K ¯ 0 mixing implies that the neutral octet-scalar mass should be larger than 400 GeV for tan β ∼ O ( 1 ) . The role of charged octet scalar in the loop of Higgs decay into diphoton is investigated. We point out that the most significant impact of this model on the diphoton decay width comes from the suppression of top-quark coupling with SM-like Higgs or even flipping its sign that leads to important enhancement in Γ ( h → γ γ ) . We also study the implications of the neutral octet-scalar contributions to the gluon fusion Higgs production cross section in alleviating the apparent tension between enhancement of diphoton decay rate and suppression of σ ( g g → h ) .

The short-distance coefficients for the color-octet 3S1 term in the fragmentation function for a gluon to split into heavy quarkonium states is calculated to order alpha_s^2. The gauge-invariant definition of the fragmentation function by Collins and Soper is employed. Ultraviolet divergences are removed using the MS-bar renormalization procedure. The longitudinal term in the fragmentation function agrees with a previous calculation by Beneke and Rothstein. The next-to-leading order correction to the transverse term disagrees with a previous calculation.

The quark flavor and spin distributions in octet baryons are calculated both in the SU(6) quark spectator diquark model and in a perturbative QCD (pQCD) based model. It is shown that the $\Lambda$ has the most significant difference in flavor structure at large $x$ between the two models, though the flavor and spin structure of other baryons can also provide tests of different models. The Drell-Yan process for $\Sigma^{\pm}$ beams on isoscalar targets can be used to test different predictions concerning the valence quark flavor structure of the $\Sigma^{\pm}$., Comment: 24 pages, 11 figures, version published in Nucl.Phys.B 574 (2000) 331

We show that the chiral $SU(n)\otimes SU(n)$ flavor symmetry on the null-plane severely restricts the sea quarks in the baryon octet. It predicts large asymmetry for the light sea quarks $(u,d,s)$, and universality and abundance for the heavy sea quarks. Further it is shown that existence of the heavy sea quarks constrained by the same symmetry reduces the theoretical value of the Ellis-Jaffe sum rule substantially., 5 pages,Talk given at ICHEP98(Vancouver)July 23--29,1998, submitted to the The ICHEP'98 conference proceedings, need ltwol2e.sty(included)

We present the results of our analysis on charmonia ($J/\psi$ and $\psi'$) hadroproduction taking into account higher-order QCD effects induced by initial-state radiation in a Monte Carlo framework, with the colour-octet mechanism implemented in the event generation. We find that those colour-octet matrix elements extracted so far from Fermilab Tevatron data for both $J/\psi$ and $\psi'$ production have to be lowered significantly. We finally make predictions for charmonia production at the LHC, presenting a code for a fast simulation with PYTHIA based on the colour-octet model., Comment: 17 pages, LaTex, 5 Figures included in the text

We discuss the chiral lagrangian for J P = 1 2 + octet and J P = 3 2 + decuplet baryons in the language of the heavy particle effective theory. We show that the effective theory qualitatively reproduces the Pauli amplitudes for the nonleptonic hyperon decays, calculated recently by Trofimenkoff. We discuss the relation of our results to nonrelativistic SU(6). We argue that we can consistently classify the meson-baryon interaction terms in lowest order in the momentum expansion according to their transformation properties under nonrelativistic SU(6). Nevertheless, the theory as a whole remains explicitly Lorentz invariant. We explain why this does not run afoul of the theorems concerning interacting relativistic SU(6) theories. We use this SU(6) classification to discuss the relation between the nonleptonic Ω − decays and the nonleptonic decays of the octet baryons. We find that the Ω − decays cannot be explained by any interaction term transforming simply under SU(6) because the nonleptonic Ω − decays do not display the pronounced ΔI = 1 2 enhancement seen in the octet hyperon decays. Any explanation of the Ω − decays requires a fine tuning of the parameters in the effective theory. We speculate that this problem may point to a flow in the basic assumption that ΔI = 1 2 four-quark operators, universally enhanced by QCD, are the dominant mechanism behind the ΔS = 1 nonleptonic decays.

Chiral corrections to baryon mass relations are computed using a chiral lagrangian which includes the spin - 3 2 baryon decuplet. The observed accuracies of the Gell-Mann-Okubo formula for baryon octet masses and of Gell-Mann's equal spacing rule for decuplet masses are consistent with chira; perturbation theory up to order m s 2 .

A calculation of the two-loop anomalous dimensions of the octet baryonic currents is presented. The anomalous dimension of the proton current is small enough and its influence on the analysis of the QCD sum rules for the proton turns out to be numerically insignificant.

Unitarity and dispersion theory are used to calculate the contribution of the π N intermediate state to the weak radiative decays of Σ and Λ hyperons. The contribution from the octet baryon poles is also calculated. The current × current form is assumed for the weak Hamiltonian so that the weak parity-violating two-body vertex vanishes in the limit of SU (3) symmetry and the parity-violating octet baryon pole terms are zero. Consequently the parity-violating weak radiative decay amplitude comes entirely from the π N intermediate state. Our main results are: (i) the contribution of the π N intermediate state is comparable to the contribution of the octet baryon pole terms and (ii) the correct sign and order of magnitude for the asymmetry parameter α and a branching ratio in moderate agreement with the recent experiment of Gershwin et al. are obtained for the decay Σ + → P γ .

Sum rules on pseudoscalar meson — meson scattering amplitudes in the physical region are studied. Our main conclusions are: (i) The too narrow width of the f meson obtained in dual models is related to the absence of a pomeron in these models and, vice versa, a pomeron may not be added to a crossing - symmetric amplitude without changing the f width. (ii) Numerically, a width of about 200 MeV, as found in a recent high-statistics ππ phase shift analysis, is preferred. (iii) The singlet/octet ratio for the tensor meson couplings is larger than predicted e.g. by the U(3) quark model.

't Hooft constructed a finite mass unit monopole by (a) embedding the electromagnetic U(1) gauge theory in an SU(2) theory via a Higgs triplet mechanism, (b) seeking solutions invariant under simultaneous rotations in ordinary and SU(2) space. We consider an SU(3) gauge theory broken down to U(2) by an octet Higgs vector and find two finite-mass stable solutions corresponding to the two ways of embedding SU(2) in SU(3). One solution is the pure unit monopole but the other, which promises to be lighter, has 1 2 unit of magnetic charge (thus violating Dirac's condition, naively applied) as well as being a source of isomagnetic flux (associated with the unbroken SU(2)).

The application of the 1/Nc expansion to the estimate of weak non-leptonic amplitudes is studied. The formulation is renormalization-group invariant and consistent with chiral symmetry. The problem of matching the short- and long-distance descriptions is properly displayed and evidence is shown for the need of more information beyond that known in these regimes. The matching problem first appears at O(1/Nc), but is important because in the 1/Nc approach the relevant octet enhancement (Δ1 = 1 2 rule ) requires large contributions from these O(1/Nc) terms.

We discuss a class of five theorems relating weak and electromagnetic form factors of the baryon octet, valid with an error of second order in the symmetry breaking for a large range of momentum transfers. The theorems are derived using simple V-spin and charge conjugation considerations. By an elementary argument we obtain a consistency condition that must be satisfied by the first-order theorems of interest, and show that this is indeed the case for our expressions. The possible application of these relations to the analysis of the semileptonic decays of the baryon octet is discussed. It is anticipated that the application of these theorems will become more useful as the information on the magnetic moments of the hyperons becomes more precise.

We show that color octet partners of leptons and weak gauge bosons can explain the exotic CERN pp collider events containing missing energy. Such exotic color partners are expected in some composite models. Our scheme predicts that e+e−-jet(s) events and e-jet(s) events will be found in future collider runs.

Within the context of basic left-right symmetry and the hypothesis of unification of weak, electromagnetic and strong forces at a mass level ≈104−106 GeV, relatively light “mass” axial gluons, confined or liberated, must be postulated. We remark that the existence of such “light” axial gluons supplementing the familiar vector octet preserves the successes of QCD, both for deep inelastic processes and charmonium physics. Through the characteristic spin-spin force, generated by their exchange, they may even help resolve some of the discrepancies between vector QCD predictions and charmonium physics. The main remark of this note is that if colour is liberated, not only vector but also axial vector gluons are produced in high-energy e−e+ experiments, e.g., at PETRA and PEP, with fairly large cross section. Distinctive decay modes of such liberated axial gluons are noted.

We generalize the bag model of hadrons to include massive quarks and investigate in particular the properties of the l = 0 octet and decimet baryons with mp = mn = 0, mλ = 270 MeV (obtained by fitting the decimet). The magnetic moments and weak axial vector/vector transition moments are calculated and compared with experimental data for cases in which data exists. We also speculate on the mechanism by which the remaining degeneracies in the baryons are lifted and on modifications which are necessary to construct a bag model of mesons.

We compute theK−π andK−π−π matrix elements of left-right four-fermion operators with Δ I = 3 2 in quenched lattice QCD andβ = 6.0, with Wilson fermions. This enables us to compute the electropenguin contributions toe′/e. We estimate:(e′/e) EMP = (0.74 ± 0.27) × 10 −3 sin φ , with φ theCP violating C-K-M phase, assuming standard values for the other C-K-M angles. Alternatively, we quoteΩ EMP ≊ 0.40 for the ratio of(ImA 2 /A 2 ) EMP to(−ImA 0 /A 0 ), the latter quantity being estimated from vacuum saturation in the continuum theory. By comparing K −π and K −π−π matrix elements, we check, within 50% errors, the soft-pion relations derived from the chiral structure of the operators. We observe a large enhancement of the matrix element 〈 π − K ¯ 0 | O | π − 〉 , which we interpret as the effect of a scalar octet pole in the π − K ¯ 0 channel. This observation has interesting implications for the related calculation of Δ I = 1 2 , K → ππweak matrix elements.

The Skyrme chiral solution is generalized to the case of u, d and s flavors of quarks and applied to the baryon octet and decuplet representations of SU(3) flavor. Numerical results are obtained for the mass spectrum and static observables.

We suggest that non-leptonic decays of charmed particles are enhanced over semi-leptonic decays by a sizeable factor, in analogy with the situation encountered in strange particle decays. This conjecture is verified in a model octet enhancement based on asymptotically-free gauge theories of strong interactions. Arguments are given to support a specific SU(3) behavior of the enhanced part of the non-leptonic Hamiltonian for charmed particle decays. Consequent selection and intensity rules are discussed.

In a high statistics CERN 2 m bubble chamber experiment the differential cross sections and polarizations of the Λ for the reactions K−p → Λπ0, Λη, Λη′ at 4.2 GeV/c have been measured. The reaction K−p → Λη exhibits a pronounced dip around −t ∼0.5 (GeV/c)2 and all three reactions show a significant backward peaking (−u < 1.0 (GeV/c)2). The Λ polarization in the reaction K−p → Λπ0 is measured to be significantly different from zero throughout most of the available t-range. Forward cross sections enable a determination of RT, the ratio of singlet/octet coupling η1KK∗∗η8KK∗∗. Backward cross sections are utilized to estimate the effective η-nucleon coupling constant gηNN2 over the −u range 0–1.5 (GeV/c)2.

A consistent treatment of color singlet and octet contributions in the spectator constituent gluon model for pseudoscalar meson decays is attempted. The result comes out one order of magnitude too small to explain the observed life-time difference of D0 and D+. Furthermore, it is found that ‘penguin’ interactions in the annihilation channel may give contributions to the asymmetry of the (D0 → K+K−)/(D0 → π+π−) ratio of the order of the phase-space difference or larger. Finally, it is argued that annihilation cannot explain the ΔI = 1 2 rule for kaon decays; dynamical effects including the penguin interactions seem still to be needed.

The successful model of Barbour and Moorhouse for pion photoproduction is extended to electroproduction and combined with recent ideas on configuration mixing or SU(6) breaking in deep inelastic electroproduction as ω → 1. We find that two consequences obtain in the current fragmentation region as ω → 1: (a) the missing mass spectrum in ep → e π − X and en → e π + X will be featureless (phase space); (b) in ep → eM +,0 X and en → eM 0,− X for any non-strange meson M the missing hadron system will contain only octets. Hence, in particular, ep → e πΔ will vanish relative to ep → e π + n as ω → 1. For K production only Λ and no Σ final states will be produced.

In a previous paper, we have shown how to systematically determine the low-energy structure of the Green functions in QCD. The present article extends this framework to expansions in the mass of the strange quark. We construct the generating functional of U(3)×U(3) which allows us to calculate the Green functions up to and including terms of order p4 (at fixed radio m quark p 2 ) in terms of a few coupling constants which chiral symmetry leaves undetermined. We calculate the first non-leading term in the quark mass expansion of the order parameters 〈0| u u|0〉, 〈0| d d|0〉, 〈0| s s|0〉 , and of the masses and decay constants in the pseudoscalar octet. The three coupling constants which are not fixed by experimental low-energy information are estimated by invoking large-Nc arguments.

The non-leptonic hyperon decays are investigated in the framework of the colored quartet model with GIM current. We take two octet components of the weak Hamiltonian which belong to 15 and 20″ representations of SU(4) symmetry. The 15 Hamiltonian arising from the symmetry breaking is assumed to have the universal spurion coupling. We obtain remarkable fits to s- and p-wave amplitudes both in the current algebra approach and the dispersion theory. It is shown that the standard arguments for s-wave decays based on the K ∗ pole dominance, on the duality arguments and on the current algebra lead to different physical consequences with one another.

We develop a formalism for describing hadronic weak annihilation decays in analogy to the treatment of deep inelastic lepton-nucleon scattering: we write down evolution equations for colour singlet and octet (Qq) systems inside mesons of increasing mass. Using D decays as input we can predict weak annihilation decay rates of heavier mesons in a semiquantitative fashion despite our ignorance on bound-state dynamics.

The currents associated with the chiral-invariant pseudoscalar meson Lagrangian, constructed from a certain metric tensor on a G-manifold, are investigated. The relation between these currents, the Sugawara model and the linearized version of chiral theories in which a set of free fields is constrained, is demonstrated. The techniques are then extended to include octets of vector and axial-vector mesons.

Current-algebra technique is used to express the S-wave hyperon decay amplitudes and the 2 π-decay amplitudes of the K S o by one-particle matrix elements of the non-leptonic parity-conserving weak interaction Hamiltonian. The experimental data show octet dominance. The matrix elements thus obtained enable us to test a hypothesis according to which the dominant parts of the parity-conserving weak, the electromagnetic and the strong interactions should to a good approximation be components of the same octet. Predictions for the ratios of one-particle matrix elements in the three different interactions turn out to be fulfilled in sign and magnitude. The results support the idea of a common dynamical mechanism for octet dominance in all three interactions.

The non-leptonic hyperon decay amplitudes are investigated under the assumption that the weak hadronic current in the CP-invariant current × current non-leptonic Hamiltonian belongs to an octet representing a mixture of a “regular” and an “irregular” octet with respect to charge-conjugation and that the irregular octet, like the regular one, belongs to the (8, 1) representation of SU(3) × SU(3). The results obtained suggest that the vanishing of the s-wave amplitude A(Σ++), for the Σ+ → n + π+ decay may be connected with the presence of irregular currents and independent of the assumption that the ΔT = 1 2 transitions predominate. The relation between reduced matrix elements leading to A(Σ++) = 0 simultaneously ensures the validity of the ΔT = 1 2 rule in Λ and Σ decays and predicts a violation of this rule for Ξ-decay.

We reproduce the cross sections σnc for nc charged particle production in high energy pp scattering, and thus obtain quasi-scaling for the KNO function 〈nc〉σnc/σinel over the energy range 50–300 GeV/c. This result is obtained in a model in which the multiperipheral secondaries originate from a chain of uncorrelated fireballs, decaying into pairs of octet vector mesons in an SU(3) singlet state, and the secondaries of diffractive type follow a Poisson distribution. At each energy, the average number 〈nc〉 of charged secondaries is taken from experiment. Then all cross sections are obtained using only one free parameter.

Inelastic meson-baryon scattering of type 0 − + 1 2 + → 0 − + 1 2 + is studied on the basis of Regge poles and exact SU3 symmetry. The exchanged trajectories considered are ϱ, A2, K∗ (890) and K∗∗ (1411). Good agreement is obtained for the differential cross section in the forward direction for different reactions. The f/d rato is found to be −11 for the 1− octet and 0.25 for the 2+ octet.

SU(3) violation for baryons is discussed on the basis of a simplified quark model with mainly scalar binding. The Λ-Σ splitting of the baryon octet and the SU(6) mass formula for the 56 representation are obtained without two-body SU(3)-breaking interactions. Mass relations are also found for resonances of higher spin, in agreement with available data for the 5 2 + octet and the 7 2 + decuplet.

The well-known soft-pion theorems for pion-baryon scattering are combined with finite-energy sum rules to (a) test the usefulness of given models of the absorptive amplitude, A + νB ; and (b) to gainn new information about the Regge exchanges. Assuming Regge terms only at intermediate and high energies ( W > 2100 MeV), and resonances at low energies, the π N sum rules predict combinations of Regge parameters in agreement with those from high-energy fits. In πΣ , πΛ scattering, the following results are obtained independently of the unknown gΣΣπ , gΣΛπ couplings: that I t = 2 exchange Regge terms must be very small; that the rho trajectory couples approximately universally to Σ; and that if P is an SU(3) singlet, then the P′ must couple to ( 1 2 + ) baryons as a mixture of both singlet and octet. We also note the difficulty of saturating the πΣ Adler-Weisberger relation, unless the sum of couplings g ΣΛπ 2 + g ΣΣπ 2 is appreciably greater then the values expected from SU(3).

This paper describes the application to parity-violating non-leptonic decays of a model of weak interactions, based on the algebra of fields definition of the hadron currents that participate in weak interactions. Symmetry breaking effects are included, octet dominance is built in explicitly and a careful treatment is given of the diagonalization procedure needed to identify the physical 0− and 1± fields. Agreement with experiment comparable to that of K∗ pole and current algebra models is achieved.

Under the assumption that axial charges couple the baryon octet only to one-particle states belonging to 1, 8, 10 SU(3) representations, sum rules for the mixing angles of the baryon wave function are derived. The results obtained from their saturation are in good agreement with the known electromagnetic properties of nucleons.

The SU(3) transformation behaviour of single-particle matrix elements 〈B′|Hw(0)|B〉 and 〈M′|Hw(0)|M〉 is investigated under the assumption that the transitions are induced by a weak current-current type quark Hamiltonian. The baryons B and mesons M are taken to be members of the 56 and 35 multiplets, respectively. For Fermi quarks the baryon matrix elements vanish identically and the meson matrix elements transform as octets. For para quarks and in the three-triplet model the baryon matrix elements transform as octets, whereas the meson matrix elements have a strong 27 component. A slightly modified Hamiltonian is introduced which induces octet transitions for both mesons and baryons.

We obtain the most general solutions to the c-number bootstrap equations a i = cd IJK (a j a k +b j b k ),b i =ed ejk a j b k where the amplitudes ai, bi represent matrix elements of unitary octet vector and axial-vector charges, respectively and c and e are arbitrary constants. For e = 2c, the equations have solutions which are consistent both with a one- and two-angle Cabibbo theory. The solutions with all physical requirements imposed still depend on three free parameters in addition to the scaling factor c. If e ≠ 2c, then the equations have no CP conserving solutions which satisfy all the requirements of Cabibbo theory.

By using an asymptotic symmetry for the SU(3) raising and lowering operator and a chiral SU(3) ⊗ SU(3) algebra, we investigate the effects of SU(3) symmetry breaking for the decay of the resonances J P = 3 + 2 , 3 + 2 , 5 + 2 , 5 − 2 into respectively baryons J P = 1 + 2 , 1 − 2 , 3 + 2 , 3 + 2 and a pion. Sum rules involving the physical masses of the particles of the 5 ± 2 octet and the 3 ± 2 decuplet and their decay coupling constants are derived. The correction to the decay amplitudes due to the breaking of SU(3) symmetry is found to be of the order of only a few percent if there is no particle mixing. Comparison with experiments (when available) is carried out. For the 3 + 2 → 1 + 2 + 0 − decays the correction is in the right direction to improve the discrepancy between the present experimental data and the prediction of exact SU(3) symmetry. However it is not enough to remove the entire discrepancy which seems to indicate the necessity of introducing some mixing effect. The sum rule for the decay 5 2 → 3 2 + 0 − shows that the F-wave decay is negligible compared to the P-wave decay. The Gursey-Radicati type intermultiplet mass formulas for the 5 2 octet and 3 2 decuplet are deduced from current algebra and the ( 5 + 2 )Ξ particle is predicted to have a mass around 2.030 MeV. This value is consistent with the value obtained from the Gell-Mann/Okubo formula and agrees well with the mass of recently found Ξ(2030).

Weinberg's spectral function sum rules have been studied in a free quark model with SU(3) breaking a la Gell-Mann, that is, the free quark Lagrangian is split into a SU(3) symmetric kinetic part, a SU(3) singlet leading to non-conservation of axial vector current and a SU(3) octet transforming like the eight-component leading to SU(3) breaking. The second sum rule modifies in this model. Though this particular model has been used as a guide to the structure of the sum rules the rules themselves are hopefully of much greater generality. The parameters representing the effect of symmetry breaking have been calculated and some applications of these sum rules have been investigated.

In this paper we discuss, within the framework of formal field theory, a more general approach to the problem of the extrapolation of the S -matrix off-mass-shell than is provided by normal PCAC. If the conventional PCAC hypothesis is used, in conjunction with the Gell-Mann, Oakes and Renner symmetry breaking model, within the pseudoscalar meson octet it predicts the relation f π = f K = f η which is badly violated experimentally. Our approach eliminates this discrepancy and provides our prime equation for the determination of the K ± p and πN scattering lengths which are the best to date. The value of the parameter m o we predict, which is the contribution to the average mass of the baryon octet due to SU (3) ⊗ SU (3) symmetry breaking, is very different from that which von Hippel and Kim find, and is of great importance in exploring the scaling properties of the hadronic Hamiltonian.

Ke4 decay data are analysed under various assumptions about the behaviour of the s-wave π-π phase shift, and the s-wave scattering length and the axial vector form factors are evaluated. An interesting feature of the analysis is the possible existence of a large vector current term. The form factor is determined and SU(3) (with vector octet dominance) used to relate this to η and η' decay. If taken literally, the results obtained are not compatible with the experimental evidence on these decays. However, the errors on the vector form factor are so large that the discrepancy is, at worst, not much more than two standard deviations. There are also several theoretical loop-holes which are discussed. The ϱ-dominance model is used to calculate the vector form factor, and the theoretical value is found to be of the order of two standard deviations below the experimental result.

The technique of asymptotic SU(3) symmetry is extended to the non-vanishing equal-time commutators between vector charges and the time-derivatives of other vector charges. Relations are obtained between the mass splittings in the 1 2 + baryon octet and the s-wave amplitudes for non-leptonic hyperon decays. Numerical results agree reasonably well with experimental data.

This is an investigation in a simple model of dynamically produced deviations from unitary symmetry. A potential analogue of a bootstrap model of vector mesons is used: the vector meson octet is treated as bound state of two pseudoscalar meson octets, the latter being bound by a vector-meson octet exchange. An approximate bootstrap solution is first obtained for the mass of degenerate vector mesons and their SU(3)-invariant coupling to degenerate pseudoscalar mesons. The mass splitting within the pseudoscalar meson octet is then considered as an input. The effects of mass splitting within the exchanged vector-meson octet and the deviations from their SU(3)-symmetric values of the coupling constants of the exchanged vector mesons to the pseudoscalar mesons are studied. It is found that the direct effect of the splitting of the exchanged mass of the bound-state mass is small; however its sign cannot be determined by naive considerations and is model dependent. It is found also that the effects of the deviations in the coupling constants cannot be ignored. A comparison is made with the work of ref. [10].

The graphical method previously used of CG coefficients of SU3 [1] is now applied to describe crossing matrices in the octet model. Useful relations about the crossing matrices previously derived mathematically by de Swart [2] are now easily shown. Besides helping visualize the physical phenomena, this method gives an easy proof of a yet unproved equality which was noticed by de Swaryt [2].

It is shown that isospin invariance for hadron states and the usual SU(2) transformation properties of electromagnetic and weak currents (CVC hypothesis) impose strong restrictions on the weak structure functions in terms of the electromagnetic ones. Among others, the inequalities Fvp+FvpFλp+Fλn ⩽ 4, − ∞ ⩽ 12(Fvp−Fvp)−3Fλp⩽32Fλn , are obtained. Furthermore, a quite restrictive scheme is obtained if one adds the following assumptions: 1. (i) Electromagnetic and weak currents are members of a SU(3) octet in the usual sense. 2. (ii) Absence of t-channel exotics. 3. (iii) Currents transform as nonets under U(3). We show that this scheme gives results which are very close to the SU(2) quark-parton light-cone models. In particular, we obtain 14⩽FλpFλn⩽4, Fvp+FvpFλp+Fλn⩽185, −6.11 Fλn ≈ (− 12+97 21)Fλn⩽12(Fvp−Fvp)−3Fvp⩽32Fλn The consequences of adding the SU(3) symmetry of hadron states are also investigated. All the statements which involve weak structure functions require as an additional assumption equality of vector and axial-vector contributions to the scattering amplitudes.

In the charge-exchange reactions π − p →π 0 n , π − p →η 0 n and K − p → K 0 n , we make the hypothesis that the amplitude is a sum of Regge poles only. Then, besides the ϱ′ pole in the first reaction, we introduce an A′ 2 pole accompanying the A 2 pole in the two other reactions. We obtain solutions where the trajectory α A2 ( t ) is linear with t and passes through J =2 at t = m A2 2 . The trajectory α A2′ ( t ) could be associated with the I =1 member of a 0 + octet, located at t ≈1 GeV 2 .

Total and differential cross sections are presented for the reactions K − p → K − p and K − p → K o n at 13 points in the c.m. energy range 1915–2168 MeV. An energy-dependent partial-wave analysis is carried out on these data together with the polarisation measurements of Daum et al. [1] and the total cross section measurements [2] within this energy range. The well known Σ(1915), Σ(2030) and Λ(2100) are observed and their resonance parameters measured. Structure is also found in the D 05 and F 07 waves. An SU(3) analysis of the 5 2 + octet, 7 2 + decuplet and 7 2 − singlet gives generally good agreement between theory and experiment except that the elasticity of the Σ(1915) is experimentally rather larger than predicted.

A one-boson-exchange (OBE) model of baryon-baryon interaction is developed. The forces are assumed to be generated by the exchange of 0−, 1− octets and a tentatively assumed 0+ octet simulating two-boson-exchange effects. To obtain the relevant coupling constants and masses of 0+ particles the Hamada-Johnston N-N potential is fitted by OBE potential. This, together with SU(3) symmetry assumed for the couplings, determines completely the Λ-N potential. The resulting potential has appeared too strong but slight adjustment of the coupling constant of the 0+ I=0 particle gave a very good agreement with the experimental data on Λ-N scattering. We find rather strong tensor force operating in the Λ-N system and this may explain the existing discrepancy between the hypernuclear and fitted estimates of the strength of the Λ-N forces.

A simple chiral model is studied for including the effects of σ-commutator terms in single-meson matrix elements of the conventional second-order electromagnetic Hamiltonian and it is conclude that they cannot be quantitatively identified with tadpole electromagnetic effects. In justifying the model, a new procedure is discussed for doing PCAC calculations with a pure octet η meson. The results of tadpole electromagnetic effects in K → 2 π decays are illustrated in the appendix.

The possible transformation properties of the energy operator under the chiral SU 3 × SU 3 algebra are investigated, assuming that it transforms as a singlet and the eighth component of an octet under SU 3 and has certain simple transformation properties under the non-strange chiral SU 2 × SU 2 . It is shown that the SU 2 × SU 2 invariant part of the energy operator can only belong to the representations (1,8) + (8,1) and (3,3 ∗ ) + (3 ∗ ,3) of SU 3 × SU 3 , as suggested by Gell-Mann, Oakes and one of the authors. Making the further assumption that the remaining part of the energy operator belongs to a four-dimensional multiplet under the non-strange chiral SU 2 × SU 2 (i.e. the pion σ-terms are isoscalar), we find its possible SU 3 × SU 3 transformation properties.

We point out a simple and (in principle) exact field-theoretic mechanism which restricts the representations in which baryons may appear in the quark model. We discuss spinless quarks in detail and show that only singlet, octet and decuplet baryons can appear. The quark dynamics arise from a field-theory bootstrap.