Showing papers on "Pseudoscalar published in 1990"
TL;DR: In this paper, the authors present an extension of their earlier observations on symmetries in operation in the weak decays of heavy mesons containing a single heavy quark, which allow them to obtain absolutely normalized model-independent predictions in the heavy quarks limit of all of the form factors for the Q1 → Q2 induced weak pseudoscalar and pseudoscalar to vector transitions in terms of a single universal function ξ(t) with ξ (0) = 1.
883 citations
TL;DR: The formalism, the potentials, and the results of this paper may also serve as a basis and a realistic starting point for systematic relativistic nuclear structure studies as well as for the investigation of further relativism many-body corrections and of contributions of higher order.
Abstract: The formalism for the Dirac-Brueckner approach to the nuclear many-body problem is described including its basis in relativistic two-nucleon scattering. A family of relativistic meson-exchange potentials is constructed which (apart from the usual coupling terms for heavy mesons) apply the pseudovector (gradient) coupling for the interaction of pseudoscalar mesons (\ensuremath{\pi},\ensuremath{\eta}) with nucleons. These potentials describe low-energy two-nucleon scattering and the deuteron data accurately. Using these potentials, the properties of nuclear matter are calculated in the Dirac-Brueckner-Hartree-Fock approximation, in which the empirical nuclear matter saturation is explained quantitatively. The effective two-body interaction in the nuclear matter medium (G matrix) is calculated directly in the nuclear matter rest frame. Thus, cumbersome transformations between the two-nucleon center-of-mass frame and the nuclear matter rest frame are avoided. Size and nature of relativistic effects included in the present approach are examined in detail. The formalism, the potentials, and the results of this paper may also serve as a basis and a realistic starting point for systematic relativistic nuclear structure studies as well as for the investigation of further relativistic many-body corrections and of contributions of higher order.
444 citations
TL;DR: In this article, the mesonic (quark-antiquark) modes in a generalized Nambu-Jona-Lasinio model with three quark flavors were analyzed.
247 citations
TL;DR: In this article, the O( α s ) QCD correction to the hadronic decay of a scalar Higgs boson was calculated, for which contradicting results have been reported.
183 citations
01 Jan 1990
TL;DR: In this paper, the decay of the neutral pion into two photons is re-examined using the non-operator field theory techniques of Source Theory, and the equivalence of pseudoscalar and pseudovector couplings is confirmed, not only for the primitive interaction, but to the next order in a.
Abstract: The historically important decay of the neutral pion into two photons is re-examined using the non-operator field theory techniques of Source Theory. The equivalence of pseudoscalar and pseudovector couplings, or alternatively, the partial conservation of the axial current, is confirmed, not only for the primitive interaction, but to the next order in a. In contrast, current algebra, which initially failed to account for the pion decay, uncovered, in the analysis of non-convergent integrals, an anomaly of the axial current divergence. This saved the day at the primitive interaction level, but does not yield the a correction. The question, of vital importance for non-Abelian gauge theories, is thereby raised but not answered: Do anomalies have physical significance, or are they mathematical artifacts of a maladroit formulation?
144 citations
TL;DR: In this paper, the amplitude for the exclusive non-leptonic decay of a heavy meson into two light pseudoscalar mesons is analyzed using the factorization formalism of perturbative QCD for exclusive reactions at large momentum transfer.
118 citations
TL;DR: In this article, a new realization of chiral SU(3) × SU (3) symmetry is discussed, which encompasses both the Wigner-Weyl mode and the Nambu-Goldstone mode.
106 citations
TL;DR: In this article, the chiral expansion of the pseudoscalar masses is re-examined, and it is shown that the observed spectrum determines the quark mass ratios mu : md : ms quite accurately.
91 citations
TL;DR: A comprehensive study of the effects related to a heavy-quark threshold in the production and decay of a scalar or pseudoscalar Higgs particle and the mixing of a Higgs boson with quarkonium states, both below and above the open-flavor threshold.
Abstract: We perform a comprehensive study of the effects related to a heavy-quark threshold in the production and decay of a scalar or pseudoscalar Higgs particle. We study the QCD corrections to the decay mode into a quark-antiquark pair and also the mixing of a Higgs boson with quarkonium states, both below and above the open-flavor threshold, which can change the properties of the Higgs boson drastically. Numerical results for a Higgs boson of mass around 10 GeV, where the mixing with {ital b{ital b}} states has a great influence on the decay widths and branching ratios, are worked out in detail for the cases of the standard model and minimal supersymmetry. The production cross section of a Higgs particle can also be enhanced by mixing with a quarkonium. A possibility to search for a Higgs boson in the 10-GeV mass range via {tau}{sup +}{tau}{sup {minus}} decays in fixed-target {ital pp} experiments at the Fermilab Tevatron or Serpukhov UNK is suggested, and ways to enhance the signal-to-background ratio are discussed.
81 citations
TL;DR: In this article, the authors simulate non-compact QED with light dynamical Kogut-Susskind fermions and confirm the existence of a second-order chiral phase transition at strong coupling.
76 citations
TL;DR: In this paper, the authors calculated the next to leading corrections to the processes γπ− → π0π− and η→ π+π−γ in chiral perturbation theory.
TL;DR: In this article, the properties of scalar, pseudoscalar, vector and axial-vector mesons and the quark condensates were studied using an extended three-flavor Nambu-Jona-Lasinio model that includes instanton-induced interactions.
TL;DR: The light scalar Higgs boson h and the pseudoscalar h and A of the minimal supersymmetric standard model have been searched for in the processes e+e−→hff and e+ e−→ hA using data collected by ALEPH at the LEP e−e− collider, with center of mass energies at and near the Z peak as mentioned in this paper.
TL;DR: In this article, the intensity of scalar and pseudoscalar particles in the reflected beam of a Bragg reflection was estimated using synchrotron radiation and a double crystal spectrometer.
TL;DR: In this paper, two-loop corrections to the coefficient functions of the dim ≤ 4 contributions to the vacuum correlator of two flavour-diagonal vector, scalar, and pseudoscalar currents are presented.
TL;DR: In this paper, the hard scattering processes γγ → PP, VV and PV (P and V denoting any member of respectively the pseudoscalar and vector nonets) are calculated in view of investigating in detail the consequences of SU(3) symmetry breaking effects.
TL;DR: In this paper, the mixing angle θP was derived from a rather exhaustive set of data including strong and radiative decays, and SU(3)-br eaking effects in terms of the constituent quark mass ratio m s / m ≅ 1.4-1.5 were taken into account whenever necessary.
TL;DR: In this paper, the pair production of the lightest scalar Higgs boson, h, and a pseudoscalar h, A, was searched for in a data sample containing 10 000 hadronic Z0 decays.
TL;DR: Using proper-time regularization, the Nambu-Jona-Lasinio model in the chiral invariant SU (2)-sector with scalar and pseudoscalar couplings is solved in the zero-boson-loop approximation for baryon number B = 1.
TL;DR: In this paper, the off-shell variations in the electromagnetic form factors of an offshell nucleon are calculated by considering the one-pion loop corrections to the vector meson dominance model.
Abstract: The off-shell variations in the electromagnetic form factors of an off-shell nucleon are calculated by considering the one-pion loop corrections to the vector meson dominance model. For the pion-nucleon interaction the pseudoscalar as well as the pseudovector coupling are considered. Meson-nucleon vertices with strong form factors are assumed and current operators are used, which satisfy Ward-Takahashi identities. Typical variations of only a few percent are found for the em form factors of the proton. Off-shell sensitivities in the kinematic situations of elastic and inelastic scattering on nuclei are considered.
TL;DR: It turns out that reasonable chiral models including only pseudoscalar fields give a zero matrix element, and taking short-distance'' effects consistently into account via the inclusion of vector mesons or explicit quarks does give a small nonzero result.
Abstract: As a preliminary we consider the phenomenology of the European Muon Collaboration experimental result without assuming SU(3) invariance. The most reliable conclusion is that the singlet axial-vector current matrix element is rather small. We calculate this matrix element in a variety of chiral-soliton models in which the axial anomaly equation is satisfied. There are a number of subtleties which we explore. It turns out that reasonable chiral models including only pseudoscalar fields give a zero matrix element. Taking "short-distance" effects consistently into account via the inclusion of vector mesons or explicit quarks does give a small nonzero result. The situation is closely analogous to the prediction of a nonzero result for the nonelectromagnetic part of the neutron-proton mass difference in these chiral models.
TL;DR: In this paper, the flip-flop model is employed to study two-baryon systems including hyperons such as Λ, Σ and Ξ and obtain a strongly bound state di-hyperon which is about 60-120 MeV lower than the ΛΛ threshold.
TL;DR: In this paper, various transition form factors in semi-leptonic decays of D-,Ds-, B- andBs-mesons using the pole dominance assumption were evaluated. But the experimental data on the transition form factor of B-means were not consistent with the quark model predictions.
Abstract: We study various transition form factors in semi-leptonic decays ofD-,Ds-,B- andBs-mesons using the pole dominance assumption. The vector current form factor is found to have only a negligible contribution to the decay rates involving pseudoscalar to vector transitions. In view of this fact we evaluate the form factors from present experimental data on the exclusive semi-leptonic decay rateΓ and the ratioΓl/ΓT of the longitudinal and transverse partial decay rates. Some non-leptonic two-body decay rates are also investigated using the factorization ansatz. Consistency with the semi-leptonic decays is found. The transition form factors of theD- andDs-mesons are found to contradict the predictions of quark model. In contrast, the experimental data on the transition form factors ofB-mesons are found to be consistent with the quark model predictions. The KM matrix element |Vcb| is determined to be |Vcb|=0.040±0.010, a value somewhat smaller than is usually chosen.
TL;DR: In this paper, a hyperbolic interaction structure was uncovered in the Dirac wave equation, which was used to generalize these equations to include pseudoscalar, pseudovector, and tensor interactions.
Abstract: In previous work, Dirac’s constraint mechanics and supersymmetry were used to construct two‐body Dirac equations for particles interacting through world scalar and vector potentials. The resulting compatible 16‐component wave equations, S1ψ=γ51(γ1⋅(p1−A1) +m1+S1)ψ=0, S2ψ=γ52(γ2⋅(p2−A2) +m2+S2)ψ=0, yield Schrodinger‐like equations in the center‐of‐momentum system with simpler structure than that possessed by the Bethe–Salpeter equation or any of its standard three‐dimensional truncations. For strong interactions, these equations have yielded a relativistic quark model for meson spectroscopy, while for electromagnetic interactions they have yielded a family of exact singlet positronium solutions. This paper uncovers a hyperbolic interaction structure in these equations. This structure is used to generalize these equations to include pseudoscalar, pseudovector, and tensor interactions.
TL;DR: In this article, the pseudoscalar nonet mass spectrum and vacuum decay constants are discussed using generalized Nambu-Jona-Lasinio models, and it is shown that in the large N c limit the bulk parameters of the pseudo-calars follow from chiral symmetry alone and do not depend on the detailed choice of the various interaction terms.
TL;DR: A lower bound of 5.4×10 −16 is shown to follow on the gravitino-photino mass ratio from the observed lack of occurrence of the processes e + e − →γS, γP, where S and P are the nearly massless chiral scalar and pseudoscalar, respectively.
Abstract: A lower bound of 5.4×10 −16 is shown to follow on the gravitino-photino mass ratio from the observed lack of occurrence of the processes e + e − →γS, γP, where S and P are the nearly massless chiral scalar and pseudoscalar, respectively. For a large class of theories with unified gaugino masses, this is convertible into a lower limit of 6.5×10 −15 GeV on the gravitino mass.
TL;DR: In this paper, the semileptonic decay rates of the τ lepton into final states containing up to three pseudoscalar mesons were calculated using a general low energy effective Lagrangian for vector mesons with chiral symmetry.
Abstract: The semileptonic decay rates of the τ lepton into final states containing up to three pseudoscalar mesons are calculated using a general low energy effective Lagrangian for pseudoscalar and vector mesons with U(3)×U(3) chiral symmetry. Symmetry breaking is taken into account in the meson masses and mixing angles. All of the coupling constants in the Lagrangian are determined empirically from vector meson decay data without additional ad hoc hypotheses such as vector meson dominance. The results compare well with the measured decay rates where data are available. No unexpectedly large branching fractions are found that might account for the “missing” decay modes of the τ.
TL;DR: In this paper, the structure of axial currents in the framework of an effective lagrangian for constituent quarks and pseudoscalar mesons is investigated, and a vanishing matrix element of the axial singlet current is seen to be related to a restricted local U(1) symmetry.
TL;DR: In this paper, the authors investigated the chiral log corrections to the electromagnetic self-energies of the pseudoscalar meson octet and demonstrated that, for the charged pions and kaons, such corrections, at scales μ ~ 1 GeV, are large.
Abstract: We investigate the chiral log corrections to the electromagnetic self-energies of the pseudoscalar meson octet and demonstrate that, for the charged pions and kaons, such corrections, at scales μ ~ 1 GeV, are large. We argue that this indicates that leading order chiral results may be misleading in the electromagnetic sector and discuss information on η → 3π and isospin breaking in Kl3 which support this interpretation.
TL;DR: In this article, the renormalization of the axial current of a nucleon bound in nuclear matter is investigated by using a chiral invariant relativistic field theory, and the role of PCAC in the medium is discussed generally and explored in detailed model calculations.