Semileptonic B decays into even parity charmed mesons

By using a constituent quark model we compute the form factors relevant to semileptonic transitions of the B mesons into low-lying p-wave charmed mesons. We evaluate the q² dependence of these form factors and compare them with other model calculations. The Isgur–Wise functions τ_1/2 and τ_3/2 are also obtained in the heavy quark limit of our results. PACS 13.25.Hw; 12.39.Hg; 12.39.Jh     

Can η mesons have a magnetic moment?

The response of pseudoscalar and vector mesons to strong magnetic fields is studied within a simple constituent quark model using analogy with bound states of Positronium. Magnetic moments of charged vector mesons K*, D*, B* are predicted and it is found that η mesons have magnetic polarizability. In extremely strong magnetic fields, behaviour of J/Ψ mesons is discussed. We speculate on the existence of an induced magnetic moment of η meson.     

Production of a charmed-meson pair in photon-photon interaction

The cross section for the exclusive production of a pair of charmed mesons in photon-photon interaction is calculated on the basis of the constituent model. The resulting predictions are compared with the predictions of heavy-quark effective theory. It is shown that the light valence quark of the D meson plays a significant role not only in hadronization but also in the process leading to the production of a heavy c quark. Moreover, it is shown that, because of the strong interaction of a primary photon field with the charge of a light quark, a similar situation persists even in the limit m _Q → ∞, whence it follows that the application of heavy-quark effective theory to the case of photon-photon interaction is incorrect, since one of the dominant mechanisms of the production of heavy mesons is disregarded in this case.     

Bound states in gauge theories as the Poincaré group representations

The bound-state generating functional is constructed in gauge theories. This construction is based on the Dirac Hamiltonian approach to gauge theories, the Poincaré group classification of fields and their nonlocal bound states, and the Markov-Yukawa constraint of irreducibility. The generating functional contains additional anomalous creations of pseudoscalar bound states: para-positronium in QED and mesons inQCDin the two-gamma processes of the type of γ + γ → π ₀ +para-positronium. The functional allows us to establish physically clear and transparent relations between the perturbativeQCD to its nonperturbative low-energy model by means of normal ordering and the quark and gluon condensates. In the limit of small current quark masses, the Gell-Mann-Oakes-Renner relation is derived from the Schwinger-Dyson and Bethe-Salpeter equations. The constituent quark masses can be calculated from a self-consistent nonlinear equation.     

Non-leptonic weak decay rate of explicitly flavored heavy mesons

It is argued quantitatively that a large difference between the D⁰ and D⁺ lifetimes is mainly due to non-perturbative long-distance effects. The total non-leptonic weak decay rates are related to the soft limit of short-distance processes. Scaling laws for the decay rates of heavy mesons with respect to mass are inferred from the QCD analysis of the soft limit of fragmentation. It is found that the decay rates are not determined by the disconnected spectator diagrams alone even in the limit of the heavy quark mass M going to infinity (< M_W), since the leading term after the QCD correction scales like M⁵ exp √clog M. Some numerical discussion is made for the decay of B mesons and T mesons.     

A study of meson-baryon couplings in the constituent quark model

Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (³P₀-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the³P₀ vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the³P₀-model, only.     

Spectroscopy with high spin selective compound reactions induced by heavy ions

The constituent symmetry group U(6) is incorporated in the null plane quark model of mesons. We obtain the value m_u=5.4 MeV, and the estimate m_s=125?160 MeV for the masses of the non-strange and the strange quarks respectively. Some checks of the model in terms of meson mass formulas are given.     

Hypothesis of Quark Binding by Condensation of Gluons in Hadrons

Hypothesis of quark binding through condensation of gluons inside hadrons is formulated in the context of a renormalization group procedure for effective particles (RGPEP) in the light-front (LF) Hamiltonian approach to QCD. At the momentum scales of relative motion of hadronic constituents that are comparable with Λ _QCD , the hypothetical boost-invariant constituent dynamics is identified using gauge symmetry. The resulting picture of mesons and baryons closely resembles constituent quark models with harmonic oscillator potentials, shares some features of AdS/QCD, and can be systematically studied using RGPEP in QCD.     

Diquark confinement in an extended NJL model

In a Nambu-Jona-Lasinio model supplemented with an infrared cutoff in addition to the ultraviolet cutoff we study the issue whether diquarks are confined when the model is extended beyond the rainbow-ladder approximation. The gap equation, obtained in a truncation scheme motivated via a non-trivial quark-gluon vertex function, is solved to determine the constituent quark mass if chiral symmetry is spontaneously broken. In a second step, the Bethe-Salpeter equations for mesons and diquarks beyond the ladder approximation are derived, taking care to preserve Goldstone's theorem in the pion channel. While the obtained masses of pseudo-scalar and vector mesons are only moderately shifted compared to the values in the ladder approximation, we observe that scalar diquarks disappear from the physical spectrum and therefore are confined. For axial-vector diquarks we observe indications that the same mechanism may also work, but the NJL model allows no conclusive answer in this channel.     

Particle trajectories and quarkonium potentials

We examine the compatibility of potential models for quarkonium with conventional Regge trajectories, exploring in particular questions of linearity and the existence of daughter trajectories. Using, for practical calculations, an effective power behaved potential, it is found that linearity of Regge trajectories is not a universal characteristic. It occurs only in a specific range of the effective quark mass, namely in the ordinary mesons. The Regge slope is in fact a decreasing function of the effective quark mass. Linearity of the ? trajectory requires the ?′ to have a mass 1.62 GeV. Altogether our results bring support to the use of quarkonium potentials in the whole range of constituent quark masses. It is argued that relativistic and non-perturbative vacuum effects give an overall shift to the masses of light mesons but do not affect much mass splittings.     

Semileptonic and Nonleptonic Decays of B s Mesons

We investigate the semileptonic and nonleptonic decays of B _s mesons. We work within the context of nonrelativistic constituent quark models. We calculate the different form factors that parameterize the hadron matrix elements.     

ηc-VV Problem in Constituent Quark Model

The problem about η_c decay into two vector mesons, such as η_c→ρρ, K* K*,φφ. are discussed in the Bethe-Salpeter framework. Both constituent quark mass and intrinsic quark transverse inchon inside the final state mesons are taken into account and their implications are discussed. The result shows that η_c→V_LV_T is stricly forbidden. Quark transverse momenta has apparent effect of enhancing the decay rate.Though both factors are included, the theoretical value is still smaller than the experimental data.     

From current to constituent quarks and the spin of the proton

We show in the context of an effective Lagrangian for baryons and pseudoscalar mesons how derivative couplings to Goldstone bosons modify the axial charges. Applying these considerations to constituent quarks we relate a modification of their axialU(1) charges to their internal structure which is represented here in term of a flavour singletφ ⁰ field attached to quarks. We end up with aSU (6)-type constituent quark model which describes the experimental results very well.     

Mass breaking in a relativistic quark model for mesons

We study symmetry breaking via quark mass differences in a relativistic quark model where mesons are built from heavy (m > 3 GeV) spin $\text{1}\text{2}$) quarks and antiquarks. The meson (squared-)mass differences are linearly related to the number of strange, charmed, etc. quarks in the mesons. We show that the previously assumed SU_n symmetry of the mesonic couplings holds, i.e., quark mass differences only show up in the masses of the external particles, not in the three meson vertex itself.     

Mass splitting of the pseudoscalar and vector mesons induced by the homogeneous vacuum gluon field

Masses of the pseudoscalar and vector mesons are calculated within the generalized Nambu-Jona-Lasinio model taking into account homogeneous vacuum gluon field. This vacuum provides an analytical quark confinement. Colorless modes are determined by the confined gluons and are described by the nonlocal quark currents with appropriate radial and angular quantum numbers. An interaction of the quark spin with the vacuum gluon field arises naturally within the model under consideration. It is shown that this spin-field interaction leads to mass splitting between vector and pseudoscalar mesons with identical quark structure (ρ-π,K-K ^* and so on). This allows to use the four-fermion coupling constant being common for both nonets.     

Static and dynamic properties of heavy light mesons in infinite mass limit

We summarize the consequences of the infinite limit of heavy quark mass in the results of form factors, charge radii and decay constants of heavy light mesons within a QCD inspired quark model recently reported.     

Pion properties at finite isospin chemical potential with isospin symmetry breaking

Pion properties at finite temperature, finite isospin and baryon chemical potentials are investigated within the SU(2) NJL model. In the mean field approximation for quarks and random phase approximation fpr mesons, we calculate the pion mass, the decay constant and the phase diagram with different quark masses for the u quark and d quark, related to QCD corrections, for the first time. Our results show an asymmetry between μI 0 and μI 0 in the phase diagram, and different values for the charged pion mass(or decay constant) and neutral pion mass(or decay constant) at finite temperature and finite isospin chemical potential. This is caused by the effect of isospin symmetry breaking, which is from different quark masses.