Showing papers on "Pseudoscalar published in 1975"

The U(1) Problem

Abstract: A detailed analysis of the problems associated with the conserved U(1) axial-vector current in quark-gluon models is presented. It is shown that such models involve a light isoscalar pseudoscalar boson, with a mass less than $\sqrt{3}{m}_{\ensuremath{\pi}}$. The existence of this boson would produce a strong off-shell variation in the $\ensuremath{\eta}\ensuremath{\rightarrow}3\ensuremath{\pi}$ matrix element, thus invalidating the usual conclusions about the rate and energy dependence of this decay. Following Kogut and Susskind, it is proposed that the light Goldstone boson is actually a dipole, with positive- and negative-metric parts, which cancel in matrix elements of gluon-gauge-invariant operators but not in operators such as the U(1) current. It is shown that the masses of the observable pseudoscalar bosons and the $\ensuremath{\eta}$ decay rate are then just as they would be in a theory without the U(1) symmetry, and in fair agreement with experiment. The application of current algebra to theories with charmed quarks is briefly discussed.

Ψ-resonances, gluons and the Zweig rule

Abstract: On the basis of the quark-gluon field theory we discuss the dynamical manifestations of gluons in hadron physics. Especially we concentrate on the Zweig rule for meson decays and the decays of the Ψ-resonances. Depending on the various possibilities for the spectrum of the glue mesons, we describe both the glue annihilation and the mixing mechanism for the Zweig-rule-violating meson decays. Furthermore we discuss the break-down of PCAC for the pseudoscalar analogue of the Ψ-meson and the importance of the glue mixing term for the mass spectrum of the pseudoscalar mesons.

Renormalization constants for scalar, pseudoscalar, and tensor currents

Abstract: We calculate the renormalization constants describing nucleon and pion matrix elements of scalar, pseudoscalar, and tensor ($S, P, T$) current densities. For certain of the constants, expressions can be obtained using standard S${\mathrm{U}}_{3}$ and chiral S${\mathrm{U}}^{3}$\ensuremath{\bigotimes}S${\mathrm{U}}^{3}$ methods. To get the remaining constants, we employ the quark model with spherically symmetric quark wave functions to relate the $S$, $P$, $T$ renormalization constants to known parameters of the usual vector and axial-vector ($V,A$) currents. We also evaluate the renormalization constants using the MIT "bag" model quark wave functions. We summarize our results in tabular form, compare the results of the various calculational methods used, and attempt to estimate the accuracy of our predictions.

Why the pseudoscalar meson mixing angle is -10$sup 0$

Abstract: We propose a simple approach to the problem of mixing in nonets which leads to an understanding of the related nature of both the ''ideal'' mixing angle of 35 degrees found for the vector and tensor mesons and the ''nonideal'' mixing angle of - 10 degrees found for the pseudoscalar mesons. We argue that the pseudoscalar meson mixing angle is ''nonideal'' because of a near degeneracy in the masses of the strange and nonstrange pseudoscalar mesons. As by-products we predict that more massive nonets will be nearly ideal and that, if charmed quarks ''exist,'' the low-lying charm--anticharm mesons will be very narrow. (AIP)

Quantization of the localized solutions in two-dimensional field theories of massive fermions

Abstract: Using the semiclassical functional method developed by Dashen, Hasslacher, and Neveu, the classical localized solutions for the bound states of massive fermions in two-dimensional field theories are quantized. The mass spectra of the bound states are then obtained. For the massive Gross-Neveu model, the mass spectrum agrees with what has been found by Dashen et al. for the massless Gross-Neveu model where fermions acquire mass through dynamical symmetry breaking. For a theory of massive fermions with scalar as well as pseudoscalar Fermi interactions, the mass spectrum is found to be very similar to that for the doublet in the sine-Gordon equation. In fact, under certain conditions they become identical.

Electromagnetic mass splittings of mesons in the charmed-quark model

Abstract: Assuming that the electromagnetic mass splitting of pseudoscalar and vector mesons results from intrinsic quark mass differences plus Coulomb and magnetic interactions, we derive inequalities among the meson masses, including the masses of charmed mesons (AIP)

Vector-meson production at large transverse momentum

Abstract: This paper considers possible extensions of the Landshoff--Polkinghorne quark-fusion model, for the production of large-p/sub T/ pseudoscalar mesons, to include the vector-meson nonet. The relative multiplicities of pseudoscalars, taking vector-meson decay into account, are calculated in two models. The leptonic decays of the rho$sup 0$, $omega$, and phi give rise to a predicted e$sup +$/$pi$$sup +$ ratio of about 5 x 10$sup -5$ in both models. Qualitative features of the models are discussed in the light of existing data on the structure of large-transverse-momentum events. (AIP)

Hadronic production of the new resonances: are gluons important

Abstract: In analogy with the Drell-Yan model for quark-antiquark annihilation into massive virtual photons, we study the possibility that the (presently) hypothetical pseudoscalar partner (${\ensuremath{\eta}}_{c}$) of the new vector resonance (${\ensuremath{\phi}}_{c}$) observed at 3095 MeV is produced via gluon-gluon annihilation. This framework allows us to estimate cross sections for ${\ensuremath{\eta}}_{c}$ production in hadronic reactions and also suggests the interesting possibility of employing ${\ensuremath{\eta}}_{c}$ production as a probe of the distributions of gluons in hadrons. In addition estimates are made for the production of pairs of charmed hadrons.

General space-time structure of the neutral-current interactions

Abstract: We present a general analysis of the neutral-current inclusive cross section taking into account all the covariants (scalar, pseudoscalar, tensor, vector, and axial-vector) in the interaction. We derive the model-independent formula for the inclusive cross section and we also discuss the consequences of various models. We deduce bounds on the ratio R equivalent sigma (nu-barN)/sigma ($nu$N) in the case in which scaling is true, i.e., the inclusive cross section at high energies is proportional to the incident neutrino energy E. The scaling violations arising from spin not-equal 1/2 partons and the bounds of R in that case are also discussed.

Electromagnetic corrections to the induced pseudoscalar term in nuclear muon capture

Abstract: We study the electromagnetic corrections to the induced pseudoscalar term in nuclear muon capture. The effects of the static nuclear magnetic field are shown to be very small. We calculate the effects of the nuclear Coulomb field by constructing the Green’s function appropriate for pions moving in the Coulomb field of an extended nucleus and using realistic muon wave functions. Consideration of finite nuclear size is shown to be imperative in order to obtain accurate results. The Coulomb corrections are not large enough to play any significant role in understanding the discrepancy of the theory with the recent measurement of the photon spectrum following radiative muon capture in40Ca of the rate of the reaction16O(μ−,νμ)16N(0−). Two approximate methods of obtaining the results are also presented.

SU(4) sigma model

Abstract: The mass spectrum of pseudoscalar and scalar mesons is discussed in a general linear SU(4) sigma model. We study the way in which the spectrum is influenced by the symmetry of the vacuum and by terms which are the analogs of quark mass terms and quark interaction terms. It is found that a paracharmonium- like state can be naturally accommodated if the charmed ''quark mass'' is much larger than the others. Other possibilities are also investigated. (AIP)

Multiple Compton scattering in the forward direction

Abstract: We prove that, to lowest order in $alpha$, the amplitude for the reaction $gamma$ + e $Yields$ n$gamma$ + e, where n = 2,3,4,..., vanishes when all n final photons have momenta parallel to that of the incident photon. We generalize this result to scalar electrodynamics, to the scattering of massless pseudoscalar (scalar) mesons off massive fermions, and to the scattering of massless scalar mesons off massive scalar mesons. (AIP)

Induced Pseudoscalar Interaction in Nuclear Beta Decay and G-Parity Nonconservation

Abstract: The pseudoscalar in weak interactions is induced by the lepton-pair decay of the pion emitted from the nucleon. In· muon capture reactions, the strength of this interaction is given by m"fp~8fA, theoretically as well as experimentallyY A possible effect of this interaction in nuclear beta decays m,ay be very small, since its effective strength is reduced by a factor 206 compared with that of the muon capture reactions. Recently, a detailed investigation of this problem was required, since the induced pseudoscalar interaction may affect the beta-ray angular distribution in polarized nuclei, and the pseudoscalar may bring an ambiguity for determining the strength of the second-class induced tensor interaction, which violates the G-parity conservation in the axial vector current.2>,s> We show here that there is no such ambiguity remammg, by calculating the particle parameters in the theory of beta decay explicitly. There are extensive investigations for the particle p~rameters by taking into account the induced effects,3> Coulomb1>, 4>7> and radiative8> corrections, and higher order nuclear matrix elements which come from the p and d waves of the leptons,1>, 4>-7> except for the induced pseudoscalar interaction. Here we give· the explicit forms for the particle parameters, which should be added to those given in the published formulasY• 4> -7> We adopt, therefore, the same notation as in the previous publications, and also the units h=me=c=l. We discuss the allowed transition only. We assume the interaction Hamiltonian density,

Spontaneous breaking of chiral symmetry in a vector-gluon model

Abstract: Solutions of the self-consistent equation for fermion propagator in a vector-gluon model are fully examined. The equation is characterized by a set of parameters, i.e., the coupling constant g, the bare mass of the fermion mo and the cutoff A. It is proved that with a suitable gauge chosen, the equation without ~utoff has solutions ·only in the case mo=O, It is then shown that, if g'/4n Bn, the "normal-state" solution for the equation without cutoff, even if it existed, should necessarily have an unphysical singularity. This fact implies that the "normal-state" solution becomes unstable for a su.fficiently large value of g'. § l. Introduction The. reason for success of low energy theorems obtained by current algebra and PCAC-treatment may be well understood in terms of chiral symmetry in which the pseudoscalar mesons play a special role among hadtons as the Nambu­ Goldstone (NG) bosons1l transforming nonlinearly under chiral transformation. On the other hand, in the composite hadron models based on SU(3) or SU(6), it is clear that there is no vital distinction between pseudoscalar mesons and others such as vector- and tensor-mesons. It is therefore worth expecting that the pseudoscalar NG bosons can also be interpreted as the bound states in con­ formity with the viewpoint of the composite model. . This homogeneity and· heterogeneity ot the pseudoscalar mesons to other mesons should rather be in­ vestigated by comparing their internal structure with composite particles· . . In this respect it would be meaningful to study a model in which spontaneous breaking of chiral symmetry is realized by a composite NG boson: The Nambu­ Jona-Lasinio model2l is known as such an example. However, the use of chain approximation and the momentum cutoff inevitable for the local four-fermion

A Dual Picture for Meson Resonances in Terms of Two Limiting Symmetries

Abstract: On the basis of lightlike chiral algebra, axial charge couplings of meson resonances are studied in terrhs of the two limiting symmetries, SU(6) 8 ®0(3)L and chiral SU(3)®SU(3). By the help of sum rules it is argued that the coexistence of SU(6) and chiral couplings attributes the breaking of one symmetry to the leakage through couplings of the other. Experimental check of this dual picture is made, though it is not conclusive due to the lack of crucial information. The concept of constituent quarks is also discussed in the lightlike formulation. § I. Introduction In previous two articles 1> we investigated a lightlike formulation of the quark model for hadrons. We studied the general structure of axial charge couplings on the non-exoticity assumption, and derived ·SUm rules of Adler-Weisberger type for lightlike chiral contents of hadron resonances. All the arguments were made without recourse to any symmetry higher than SU(3). The aim of this article is to discuss how our approach can be concerned with the symmetry pattern of hadrons. This is an important problem for the lightlike formulation, because lightlike chiral algebra•> is characterized by its commutativity with the stability group Y(r), which does not contain p-. It is our basic standpoine> that the non-symmetry nature of SU(3) 1Q!;;SU(3) 1 essentially arises from the spontaneous breakdown of chiral symmetry. 4> The ap­ proximate realization of chiral symmetry through the Goldstone-Nambu mechanism provides us with a ·theoretical basis for the partially conserved axial-current hypoth­ esis.5> By this hypothesis we can relate axial charge couplings to pseudoscalar octet meson (P8) vertices in terms of the relation 8>

η and η′ Meson Mixing in U(6) Symmetry

Abstract: 1meson are also discussed. The composite inodel in which the baryon and the meson are composed of urbaryons as (uuu) and (uu) respectively ·has brought us systematic understand­ ing of the hadron spectrum and their interactions. At high energies, several sum rules among differential cross sections of various hadronic reactions have been derived 1l from counting the urbaryon rearrangement amplitudes with the Okubo-Iizuka rule2l which forbids the disconnected urbaryon diagram. The sum rules well agree with experiments. Recently it has been argued 8l' 4l that the sum rules among the differential cross sections concerning r; or r;' meson derived from the simple counting rule do not agree with experiments, i.e., the singlet octet ratio S =(I r;1) /(I r;s) is introduced as a free parameter and its value is found to be much smaller than .J2 obtained from the simple counting rule when high energy hadronic reactions and strong decays are concerned. From the standpoint of the urbayon model, a correction to the simple count­ ing rule is naturally interpreted as an effect of the overlapping integral between the hadrons and it is related to the mass formula of pseudoscalar mesons. In the U(6) symmetry theory, one of the pseudo scalar mesons with I= Y = 0 belongs to 1 of U(6) multiplets and the other eight pseudoscalar mesons and nine vector mesons belong to 35. It can be considered that, in the first ap­ proximation, the spatial wave functions of the 35 states are equal to each other and different from that of the 1 state and the U(3) invariant mass terms split into 1 and 35. The U(3) symmetry breaking terms T 8 8 well reproduce the

Production of large-transverse-momentum mesons and lepton pairs in proton-antiproton collisions

Abstract: The production of large-pT pseudoscalar mesons and leptons in\(p\bar p\) collisions is studied in the quark-parton model of Landshoff and Polkinghorne. Explicit model calculations of the quark fusion process show that, due to valence-quark exchange from both colliding hadrons,\(p\bar p\) single-particle inclusive cross-sections will be significantly larger than the corresponding pp cross-sections. The direct quark-hadron scattering process is also discussed.

Quantization of torsion in a space of zero Riemannian curvature

Abstract: Starting from the general form of the Lagrangian (quadratic with respect to the curvature tensor), the free torsion field and its interaction with spinor matter is considered for the particular case of a zero Riemann—Christoffel tensor. It is shown that the torsion field is equivalent to the superposition of the wave functions of massive axial-vector, massless and massive pseudoscalar particles (torsions). In addition to this, an axial-vector torsion is generated by the divergenceless part of the spin pseudovector of matter, and pseudoscalar torsions by the divergence of this pseudovector.

Leptonic decays of heavy pseudoscalar mesons

Abstract: The authors identify the new particles psi (3100) and psi ' (3700) as the /b I/=0 members of a heavy-meson nonet and the wide bump at 4100 MeV, denoted by psi " as the neutral /b I/=1 member of the corresponding octet. They propose that these hadronic states are built from an SU/sub 3/ triplet (p', n', lambda ') of heavy quarks which includes an isodoublet (p', n') and an isosinglet lambda ', just like ordinary hadrons are supposed to be made from the (p, n, lambda ) quarks. The electric charges of p' and n' are taken to be either /sup 2 ///sub 3/ and -/sup 1///sub 3/ or 1 and 0, respectively. Other quantum numbers are left unspecified in the present analysis.

Dynamical symmetry breaking, renormalizability and phenomenological Lagrangians

Abstract: The dynamical symmetry breaking of a chiralU1×U1 invariant model is considered. Assuming the existence of a massless pseudoscalar bound state, which decouples, and a massive scalar bound state, we deduce sufficient conditions of renormalizability of the symmetry-broken theory using phenomenological Lagrangians. We comment on the feasibility of dealing with these conditions.