The effects of configuration mixing on excited charmonium decays

Configuration mixing betwenn ψ, ψ′ and ψ″ is considered in two models. In one model the confining potential consists of a scalar and a vector part; in the other model the vector confining potential interacts with a colour anomalous magnetic moment. It is shown that strong configuration mixing affects theEl transition rate and electronic decay widths of the vector mesons considerably.     

Scalar mesons in a chiral quark model with glueball

Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3)×U(3) chiral quark model of the Nambu-Jona-Lasinio (NJL) type with 't Hooft interaction. The latter interaction produces singlet-octet mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and the glueball and their main modes of strong decay are described. Received: 14 July 2000 / Accepted: 31 July 2000     

Spectroscopy of atomlike mesonsQ \bar q in the dirac equation with scalar confining potential

Spectroscopy of atomlike mesons composed of one heavy quarkQ and one light quark \(\bar q\) is studied in the Dirac equation with (i) scalar power law potential, (ii) scalar logarithmic potential and (iii) Coulomb plus scalar linear potential. It is found that the potentialr ^0.1 gives an excellent fit toD, F andB mesons together with Ψ and Υ families treated in the nonrelativistic theory, and that the light quark masses in atomlike mesons are very close to the current quark masses.     

Spin-dependence and glueball mixing with θ(1640) in ordinary meson spectroscopy

It is shown from a fairly general point of view that meson spectroscopy implies that the spin-spin and tensor forces are due to very short-ranged interactions. The (Q₁, Q₂) ? (Q_A, Q_B) mixing of axial vector $\text{I =}\text{1}\text{2}$ mesons implies the presence of a substantial repulsive Thomas term as well as an attractive short-ranged spin-orbit force of comparable magnitude. This analysis makes no reference to detailed potentials or wave functions. Inverted multiplets are predicted as a consequence of the large repulsive Thomas term. The spin-dependent potentials can be interpreted as effective exchanges dominated by short-ranged vector exchange and a confining potential transforming as a Lorentz scalar, although small amounts of other exchanges are also possible. A model-dependent analysis of the gluon annihilation contribution to the mass matrix and two-body decays of the I = 0 2⁺⁺ mesons indicates significant gluon mixing in these states. The presence of a $\text{non-q}\text{q}$ state (glueball?) which mixes with f'(1514) and another I = 0 2⁺⁺ state is required by the mixing model. The possibility that this additional state is θ(1640) is considered. The mass of such a state satisfies f'(1514)<M(G₀)<θ(1640). The model predicts $\text{0.01 < Λ(θ → ηη)/Λ(θ →}\text{K}\text{K}\text{)<0.18}$, with the actual widths sensitive to the details of singlet-octet mixing in the η wave function.     

Masses of colored vector mesons

Mass formulas for colored vector mesons are derived under the assumption of one common mixing angle forSU(3)′, independent of the color quantum numbers, and correspondingly one common mixing angle (?″) forSU(3)″. This a priori plausible assumption turns out to have strong implications and thus might be too restrictive. We allow for a non-trivial spatial overlap integralρ between color-singlet and color-octet states. Various cases are treated and physical possibilities are identified. The best agreement is obtained for ?″ = 0. There are two models of this type with and without a part of the symmetry breaking Hamiltonian density transforming as (Y, Y) underSU(3)′?SU(3)″. Models with ?″ ≠ 0 are also possible. They cannot have a (Y, Y) and predict 3.34 GeV as the mass of theψ′ (3.7). This error of 10% may however be used to reject this possibility. Masses of colored vector mesons are predicted in the various models. If a (Y, Y) is present, ideal mixing inSU (3)′ is implied by the general formalism of the model.     

CP-Violation parameters in the two Higgs doublets model

The perturbative unitarity constraints on the CP-violation parameters in the neutral scalar mesons sector are examined for the standard model extension involving two scalar Higgs doublets. The top- and bottom-quark condensates approach is employed, but we also use the alternative renormalization group approach based on the assumption that the coupling constants of the hard Yukawa and self-coupling scalar mesons interactions reach approximate infrared fixed points at the electroweak scale. The perturbative unification scale,F _X , the charged Higgs bosons mass, the complex CP-violation phase and eventually the ratio of vacuum expectation values of the neutral scalar fields constitute the sole free parameters. We evaluate numerically the CP-violation parameters, Imz _i , representing the mixing of scalar and pseudoscalar mesons as a function of these parameters. The allowed ranges for Imz _i are found to lie far below the unitarity bounds obtained by Weinberg.     

Contact electromagnetic terms in inclusive photo- and electroproduction

It is shown that contact electromagnetic terms in the photo- and electroproduction exclusive channels can account for a substantial amount of the inclusive real and virtual γp total cross sections. In particular, one gets σ(γp)_exp?σVMD (?, ω, φ) + σ(contact) for Q²=0 and hence no infinite vector mesons (GVMD) seem to be required. The same result is valid for Q²<0. A parallelism with the parton approach is noted.     

QCD with Chiral Chemical Vector: Models Versus Lattices

A formation of Local Parity Breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. LPB in the fireball can be produced by a difference between the number densities of right- and left-handed chiral fermions (Chiral Imbalance) which is implemented by a chiral (axial) chemical potential. Based on the effective meson Lagrangian motivated by QCD in the chiral medium the properties of light scalar and pseudoscalar mesons (π, a₀) are analyzed. It is found that exotic decays of scalar mesons arise as a result of mixing of π and a₀ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We believe that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.     

The mixing and decays of isoscalar mesons

The predictions of a linear mass mixing model for pseudoscalar and vector mesons, which incorporates the effects of radial excitations, are examined. Several analyses are made fitting in each case to a different experimental value of $\text{Γ(ψ →η'γ)}\text{Γ(ψ→ηγ)}$ upon which the η-η′ mixing pattern is very sensitive. Predictions for radiative transitions among the mesons and for the ratio of production amplitudes $\text{σ}\text{(π}{}^{\mathrm{?}}\text{p→η′n)}\text{σ}\text{(π}{}^{\mathrm{?}}\text{p→ηn)}$ are compared with experiments. Results indicate a preferred value of 3.1 for $\text{Γ(ψ→η′γ)}\text{Γ(ψ→ηγ)}$.     

Mass shift of σ-meson in nuclear matter

The propagation of σ-meson in nuclear matter is studied in the Walecka model, by assuming that the sigma couples to a pair of nucleon–antinucleon states and to particle–hole states. The in-medium effect of σ–ω mixing is also studied. For completeness, the coupling of sigma to two virtual pions was also considered. It is found that the σ-meson mass decreases with respect to its value in vacuum and that the contribution of the σ–ω mixing effect on the mass shift is relatively small.     

Finite temperature effect in infrared-improved AdS/QCD model with back reaction of bulk vacuum

Based on an IR-improved soft-wall AdS/QCD model for mesons,which provides a consistent prediction for the mass spectra of resonance scalar,pseudoscalar,vector and axial-vector mesons,we investigate its finite temperature effect.By analyzing the spectral function of mesons and fitting it with a Breit-Wigner form,we perform an analysis for the critical temperature of mesons.The back-reaction effects of bulk vacuum are considered and the thermal mass spectral function of resonance mesons is calculated based on the back-reaction improved action.A reasonable melting temperature is found to be T_c≈150 ± 7 MeV.which is consistent with the recent results from lattice QCD simulations.     

Low-Energy Scattering of Heavy-Light Mesons from Nucleons

We study the low-energy scattering of charmed (D) and strange (K) mesons by nucleons. The short-distance part of the interaction is due to quark-gluon interchanges derived from a model that realizes dynamical chiral symmetry breaking and confines color. The quark-gluon interaction incorporates a confining Coulomb-like potential extracted from lattice QCD simulations in Coulomb gauge and a transverse hyperfine interaction consistent with a finite gluon propagator in the infrared. The long-distance part of the interaction is due to single vector (??, ??) and scalar (??) meson exchanges. We show results for scattering cross-sections for isospin I?=?0 and I?=?1.     

Photon propagation function and charged vector mesons

The one-loop contribution to the photon propagation function due to the exchange of a pair of vector mesons is presented in the context of source theory. An arbitrary magnetic moment κ is considered and the derived spectral form has the expected ultraviolet divergence (logarithmic when κ = 0, and linear when κ ≠ 0). This difficulty can be circumvented in the case κ = 0, when making use of a non-causal method based on the euclidean postulate, as stated in source theory, and Schwinger's modified propagation function for spin-1 particles, as derived by the author elsewhere.     

Gluon exchange in meson spectroscopy

We discuss the spin structure ofN=L=0 andN=L=1 mesons in terms of the one-gluon exchange model with scalar confinement of quarks. SU(3)_flavour is broken by taking different masses for the quarks and the SU (3) breaking of the nonperturbed hamiltonian is shown to be very important in understanding the hyperfine splittings in the ground state mesons, including the charmed states. A fit to the experimental mass spectrum is performed for theN=L=0 andN=L=1 levels simultaneously. The spin-orbit splittings of the spectrum cannot be explained by the convential terms from gluon exchange and scalar confinement. We argue that additional terms, which break the ideal mixing pattern, have to be present. The inclusion of such a term gives a dramatic improvement in χ² and leads to an almost perfect fit to the data for masses and mixing angles.     

Instanton-induced flavour mixing in mesons

The U_L(N_f)×U_R(N_f) chiral symmetric version of the Nambu-Jona-Lasinio model is extended by the 't Hooft determinant and bosonized for an arbitrary number of flavours N_f. The resulting effective meson lagrangian is explicitly calculated to leading order in the derivatives for three flavours. The 't Hooft determinant induces flavour mixing of the mesons with diagonal flavour content (π⁰, η, η′, and their scalar chiral partners δ⁰, S, ϵ) and pushes up the physical η′-mass. The η-η′ mixing angle is found to be −31°.     

Inverted charmed meson multiplets as a test for scalar confinement

It is shown that an effective quark-antiquark confining force, transformation as a Lorenzt scalar, leads to inverted P-wave multiplets of charmed and bottom mesons. This prediction is a qualitative feature due to a kinematical enhancement of a long-range effective scalar exchange relative to the short-range vector exchange, and is not overly sensitive to quantitative details. The discovery of such inverted meson multiplets would provide dramatic confirmation of scalar quark confinement.     

Decays τ → (η, η')<Emphasis Type="Italic">K</Emphasis>–ν<Subscript>τ</Subscript> in the extended Nambu–Jona-Lasinio model

The decays τ → (η, η')K–ν_τ are described in the framework of the extended Nambu–Jona-Lasinio model. Both full and differential widths of these decays are calculated. The vector and scalar channels are considered. In the vector channel, the subprocesses with the intermediate K*(892) and K*(1410) mesons play the main role. In the scalar channel, the subprocesses with the intermediate and K₀^*(800) and K₀^*(1430) mesons are taken into account. The scalar channel gives an insignificant contribution to the full width of the decay τ → ηK–ν_τ. The obtained results are in satisfactory agreement with the experimental data. The prediction for the width of the process τ → η′K–ν_τ is made.     

Lineare Polarisation der Bremsstrahlung von 2 MeV-Elektronen

In a preceding work a system of nucleon-antinucleon with the quantum numbers of various existing scalar and pseudoscalar particles was studied with a Bethe Salpeter equation in the ladder approximation. That analysis is now extended to vector particles, that is to bound states with the quantum numbers of theω, ρ, φ. The interaction is produced as in the preceding work byπ mesons, plus a phenomenological vector interaction. The conclusions for scalar and pseudoscalar particles are confirmed also for the vector states: that is to obtain the experimental value for the coupling constant \(g_{N\bar N\pi } \) the used model requires for a cut off values between 1 to 4 nucleonic masses; the effect of the vector interaction is always attractive.     

Meson loops in the f0(980) and a0(980) radiative decays into ρ , ω

We calculate the radiative decay widths of the a ₀(980) and f ₀(980) scalar mesons into ργ and ωγ considering the dynamically generated nature of these scalar resonances within the realm of the chiral unitary approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two-meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.     

Electromagnetic interactions in a chiral effective lagrangian for nuclei

Electromagnetic (EM) interactions are incorporated in a recently proposed effective field theory of the nuclear many-body problem. Earlier work with this effective theory exhibited EM couplings that are correct only to lowest order in both the pion fields and the electric charge. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields. The theory exhibits a nonlinear realization of SU(2)_L × SU(2)_R chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. It has been verified that for normal nuclear systems, the effective lagrangian can be expanded systematically in powers of the meson fields (and their derivatives) and can be truncated reliably after the first few orders. The complete EM lagrangian arising from minimal substitution is derived and shown to possess the residual chiral symmetry of massless, two-flavor QCD with EM interactions. The uniqueness of the minimal EM current is proved, and the properties of the isovector vector and axial-vector currents are discussed, generalizing earlier work. The residual chiral symmetry is maintained in additional (non-minimal) EM couplings expressed as a derivative expansion and in implementing vector meson dominance. The role of chiral anomalies in the EM lagrangian is briefly discussed.