Effective meson lagrangian with chiral and heavy quark symmetries from quark flavor dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)_F symmetry breaking effects are estimated and, if possible, confronted with experiment.     

Charm diffusion in a pion gas implementing unitarity, chiral and heavy quark symmetries

We compute the charm drag and diffusion coefficients in a hot pion gas, such as is formed in a heavy ion collision after the system cools sufficiently to transit into the hadron phase. We fully exploit heavy quark effective theory (with both D and D^∗ mesons as elementary degrees of freedom during the collision) and chiral perturbation theory, and employ standard unitarization to reach higher temperatures. We find that a certain friction and shear diffusion coefficients are almost p²-independent at a fixed temperature which simplifies phenomenological analysis.At the higher end of reliability of our calculation, , we report a charm relaxation length , in agreement with the model estimate of He, Fries and Rapp.The momentum of a 1 GeV charm quark decreases about 50 MeV per fermi when crossing the hadron phase.     

Hierarchical chiral symmetries and the quark mass matrix

A hierarchical pattern of chiral symmetries is introduced, whose breaking is supposed to lead to the observed hierarchical pattern of the quark mass spectrum. Specific consequences for the interplay between the quark masses and the weak interaction mixing parameters are derived, in accordance with the observational constraints. They can be regarded as stringent constraints for any realistic dynamical theory of the quark mass spectrum. CP violation is absent in the limit m_u=m_d=0. A specific way to describe the weak interaction mixing emerges.     

Two body non-leptonic decaysB →Dπ with heavy quark and chiral symmetry

We have analysed the two body non-leptonic charmed-meson decays of heavyB meson based on the factorization assumption. The transition matrix elements and the corresponding decay widths are calculated in the heavy quark and chiral symmetry limit and the Isgur-Wise function present in the expression is determined by the wave function model of Aliet al. The results obtained are quite interesting and agree reasonably well with the experimental data.     

Self-energy of heavy quark

We demonstrate that to calculate the selfenergy of a heavy quark in the heavy quark limit (or the heavy fermion limit in what is called the Baryon Chiral Perturbation Theory), the use of standard dimensional regularization provides only the quantum limit: opposite to the heavy quark (or classical) limit that one wishes to obtain. We thus devised a standard ultraviolet/infrared regularization procedure in calculating the one- and two-loop contributions to the heavy quark self-energy in this limit. Then the one-loop result is shown to provide the standard classical Coulomb self-energy of a static colour source that is linearly proportional to the ultraviolet cutoff Λ. All the two-loop contributions are found to be proportional to Λ In (Λ/γ) where γ is the infrared cutoff. Often only the contribution from the bubble (light quarks, gluon and ghost) insertion to the gluon propagator has been considered as theO(α _s ) correction to the Coulomb energy to this order. Our result shows that other contributions are of the same magnitude, thus have to be taken into account.     

Nonlinear realization of chiral symmetries and localizability

We prove that the nonlinear realization ofS U(n)×S U(n) (n3) is uniquely determined by the requirement that the Lagrangian, with a minimal number of derivatives of those fields parametrizing the adjoint representation of the diagonalS U(n) subgroup, is localizable in the sense of Jaffe.     

Calculating heavy quark distributions

A systematic calculation of the evolution of parton distribution functions including the effects of heavy-quark masses is presented. The method involves the use of a special renormalization scheme which ensures ordinary massless evolution with the correct number of active quark flavors at all stages, and specifies appropriate matching conditions at thresholds. This method is applicable to all orders of the perturbation expansion in principle, and it is simple to implement in practice. Results of this calculation using known distributions at low energies as input are examined and compared with published results. The heavy-quark distribution functions are found to be about a factor of two larger than the well-known EHLQ results.     

Broken chiral symmetries and light composite fermions

We elaborate on a mechanism for obtaining naturally light composite fermions in a strongly interacting gauge theory. A simple toy model is used to illustrate the basic ideas.     

Photoproduction of heavy quark flavours

Within QCD the photoproduction of new heavy flavours proceeds via photon-gluon amalgamation. The production cross sections of new particles (charm, top, bottom, …) are calculated. Photon and lepton beams are better suited than hadron beams for producing the new particles.     

Roper resonances in chiral quark models

We derive a method to calculate the multi-channel K -matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the and N ( channels where the -meson models the correlated two-pion decay. We solve the integral equation for the K -matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the (1232) and the N(1440) resonances compared to the bare quark values.     

H-particle in a chiral quark model

In this paper we discuss the binding energy of the H-particle using a chiral quark model, where pion exchange plays an important role to reproduce the mass difference between the nucleon and Δ resonance. Since the main source for the bound H-particle is believed to be the color magnetic interaction, which gives the nucleon and Δ mass difference, it is very interesting to investigate whether the chiral quark model gives rise to the bound H-particle or not. We employ an extended resonating group method in order to take into account the possibility of a change of baryon wave functions when two baryons interact with each other. We found that a change of baryon size together with the Hamiltonian which consists of gluon, pseudoscalar meson and sigma meson exchange potentials gives rise to the bound H-particle. The binding energy is found to be about 25 MeV in a hybrid chiral quark model. Differences between the ordinary gluon dominant model and chiral quark models are also investigated. It is found that a pure chiral model has no bound state when the widely used sigma-quark coupling strength is employed.     

Weak magnetism in chiral quark models

We discuss symmetry breaking in the weak magnetism form factors for the semileptonic octet baryon decays. In the chiral quark model, the symmetry breaking can be accounted for in the masses and the quark spin polarizations can take on more general values due to Goldstone boson depolarization. Here we clarify some features of the chiral quark model prediction for the weak magnetism and compare to the corresponding result of the chiral quark soliton model. Received: 29 June 1999 / Revised version: 15 September 1999 / Published online: 8 December 1999