Quenched light hadron spectrum

We present results of a large-scale simulation for the flavor nonsinglet light hadron spectrum in quenched lattice QCD with the Wilson quark action. Hadron masses are calculated at four values of lattice spacing in the range a approximately 0.1-0.05 fm on lattices with a physical extent of 3 fm at five quark masses corresponding to m(pi)/m(rho) approximately 0.75-0.4. The calculated spectrum in the continuum limit shows a systematic deviation from experiment, though the magnitude of deviation is contained within 11%. Results for decay constants and light quark masses are also reported.     

A model of flavor mixing

A model of quark mass matrices is presented where flavor mixings can be expanded in powers of small parameters. These parameters characterize the observed quark mass pattern. The weak mixing matrix has a very simple form. The correlation of the weak mixing angles and CP-violating phases with the main features of the quark spectrum may be easily studied. An upper bound is predicted on the top-quark mass, m_t^p⩽45 GeV, and a rate for the b→u transition close to its experimental limit.     

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.     

Pion and chiral density waves in a (1 + 1)-dimensional Nambu-Jona-Lasinio model

A (1 + 1)-dimensional massless Nambu-Jona-Lasinio model is investigated in the limit of a large number of colors. The model describes a system with two quark flavors if μ baryon and μ _I isospin chemical potentials occur. The question of whether spatially inhomogeneous chiral and pion condensates can form in a dense quark environment is also examined.     

Coherent vector gluon field in hadrons

A vector cohesive field in a hadron is treated in the classical limit. An asymptotic boson mass spectrum is derived, which becomes linear for infinitely heavy quarks. The size of the wave functions are scaled by the bare quark mass.     

QCD interactions of heavy mesons with pions by light-cone sum rules

Light-cone QCD sum rules are employed to compute the strong coupling constants: , and , where and are negative and positive parity and doublets. The couplings are calculated both for finite values of the heavy quark mass and in the infinite heavy quark mass limit, deriving sum rules for . Received: 30 May 1997 / Revised version: 7 October 1997 / Published online: 23 February 1998     

Gauge-invariant formalism and quark confinement in QCD2

New gauge-invariant vector and spinor fields are introduced. Gauge-invariant quark propagator is defined in terms of these new fields. The equation for such a propagator, taken in 1/N approximation, does not require the introduction of an infrared regularization. As the regularization parameter in our approach there stands such a parameter which limit value corresponds to the gauge-invariant fields and translationally invariant quark propagator. It is shown that in this limit the pole of the gauge-invariant quark propagator shifts towards infinity what is usually treated as the confinement of a single quark.     

Leading chiral contributions to the spin structure of the proton

The leading chiral contributions to the quark and gluon components of the proton spin are calculated using heavy-baryon chiral perturbation theory. Similar calculations are done for the moments of the generalized parton distributions relevant to the quark and gluon angular momentum densities. These results provide useful insight into the role of pions in the spin structure of the nucleon and can serve as a guide for extrapolating lattice QCD calculations at large quark masses to the chiral limit.     

Construction of Bethe Salpeter wave functions and applications in QCD

We suggest an ansatz for the Bethe Salpeter wave function which is strictly covariant, obeys the spectrum conditions, and has the correct non relativistic limit. As a first simple application we present a wave function for the pion. It contains two parameters, one of them being the quark mass. The decay constant and the form factor derived from this are in excellent agreement with the data.     

Emergence of a nonuniform pion condensate in the (1 + 1)-dimensional Nambu-Jona-Lasinio model

The (1 + 1)-dimensional Nambu-Jona-Lasinio model describing the system of two-flavor quarks is studied in the limit of a large number of colors in the presence of a baryon chemical potential µ and an isospin chemical potential µ _I . The possible formation of a nonuniform pion condensate in dense quark matter is considered for the cases of both the massive and the massless model.     

Heavy quark induced effective action for gauge fields in the SU(N_c)\otimes U(1) model and the low-energy structure of heavy quark current correlators

We calculate the low-energy limit of heavy quark current correlators within an expansion in the inverse heavy quark mass. The induced low-energy currents built from the gluon fields corresponding to the initial heavy quark currents are obtained from an effective action for gauge fields in the one-loop approximation at the leading order of the expansion. Explicit formulae for the low-energy spectra of electromagnetic and tensor heavy quark current correlators are given. Consequences of the appearance of a nonvanishing spectral density below the two-particle threshold for high precision phenomenology of heavy quarks are discussed quantitatively. Received: 21 April 2001 / Revised version: 18 May 2001 / Published online: 29 June 2001     

Search for quark compositeness with the dijet centrality ratio in pp collisions at √s=7 TeV

A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at √s=7 TeV, is described. The data sample of the study corresponds to an integrated luminosity of 2.9 pb(-1) collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the standard model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.     

The swelling of nucleons and quark antisymmetrization

Antisymmetrization of the nuclear wavefunction at the quark level implies that quarks belonging to different nucleons are exchanged in proportion to the degree of nucleon overlap. This leads to an additional contribution to the quark-quark correlation beyond that expected in a conventional picture. We first explore this in a simple solvable one-dimensional model. Subsequently an extension is made to a model of nuclear matter for which divergences are encountered in the limit of large N. These are traced to the existence of unlinked quark clusters. After renormalization, the quarkquark correlation is computed. It is concluded that quark antisymmetrization leads to an effective nucleon size which depends on the nuclear density. A simple analytic formula for the effective nucleon radius is obtained.     

Aspects of the confinement mechanism in Coulomb-gauge QCD

Phenomenological consequences of the infrared singular, instantaneous part of the gluon propagator in the Coulomb gauge are investigated. The corresponding quark Dyson-Schwinger equation is solved, neglecting retardation and transverse gluons and regulating the resulting infrared singularities. While the quark propagator vanishes as the infrared regulator goes to zero, the frequency integral over the quark propagator stays finite and well defined. Solutions of the homogeneous Bethe-Salpeter equation for the pseudoscalar and vector mesons as well as for scalar and axial-vector diquarks are obtained. In the limit of a vanishing infrared regulator the diquark masses diverge, while meson properties and diquark radii remain finite and well defined. These features are interpreted with respect to the resulting aspects of confinement for colored quark-quark correlations.     

The top quark mass and flavour mixing in a seesaw model of quark masses

The top quark mass and the flavour mixing are studied in the context of a seesaw model of quark masses based on the gauge group SU(2)_L × SU(2)_R × U(1). Six isosinglet quarks are introduced to give rise to the mass hierarchy of ordinary quarks. In this scheme, we reexamine a mechanism for the generation of the top quark mass. It is shown that, in order to prevent the seesaw mechanism to act for the top quark, the mass parameter of its isosinglet partner must be much smaller than the breaking scale of SU(2)_R. As a result the fourth lightest up quark must have a mass of the order of the breaking scale of SU(2)_R, and a large mixing between the right-handed top quark and its singlet partner occurs. We also show that this mechanism is compatible with the mass spectrum of light quarks and their flavour mixing.     

Universal,Solution of Oppenheimer-Volkov Equatiops for Strange Stellar System Based on the MIT Bag Model

The universal solution of Oppenheimer-Volkov equations with strange quark matter equation of state of the MIT bag model is calculated in a reduced form which is independent of the MIT constant B. The lower limit of the observational pulse period of pulsars (0.69 ma) is predicted by the MIT bag constant B=(146 MeV)⁴ which ia fitted to the hadronic spectrum, while the observed lower limit of pulse period of pulaara (1.56 ms) gives an astrophysical restriction on the lower limit of the MIT bag constant as B>(97 MeV)⁴.     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted ma...     

Effect of orbital angular momentum on valence-quark helicity distributions

We study the quark helicity distributions at large x in perturbative QCD, taking into account contributions from the valence Fock states of the nucleon which have nonzero orbital angular momentum. We find that the quark orbital angular momentum contributes a large logarithm to the negative helicity quark distributions in addition to its power behavior, scaling as (1-x){5}log{2}(1-x) in the limit of x-->1. Our analysis shows that the ratio of the polarized over unpolarized down quark distributions, Deltad/d, will still approach 1 in this limit. By comparing with the experimental data, we find that this ratio should cross zero at x approximately 0.75.