A Diquark-Quark Model with Its Use in Nucleon Form Factors

The nucleon electromagnetic form factors are investigated within a simple diquark-quark model using the light-front formalism. In this model, baryon is described as a bound state of one quark and one clustering diquark.The calculational results are compared with the experimental ones. We also regard the quarks in a baryon as pointlike constituent quarks.     

Baryon bound state in two-dimensional SU(N) gauge theory

The bound-state baryon problem with N quarks in an SU(N) gauge model of strong interactions is investigated in one-space and one-time dimensions. A study of planar diagrams yields color singlet “baryon” states of quarks that have infrared divergence-free mass spectra. The resulting integral equation turns out to be identical to the one obtained in a particular string model.     

The thermodynamic properties of weakly interacting quark-gluon plasma via the one-gluon exchange interaction

The thermodynamic properties of the quark-gluon plasma (QGP), as well as its phase diagram, are calculated as a function of baryon density (chemical potential) and temperature. The QGP is assumed to be composed of the light quarks only, i.e., the up and down quarks, which interact weakly, and the gluons which are treated as they are free. The interaction between quarks is considered in the framework of the one gluon exchange model which is obtained from the Fermi liquid picture. The bag model is used, with fixed bag pressure (B)for the nonperturbative part, and the quantum chromodynamics (QCD) coupling is assumed to be constant, i.e., with no dependence on the temperature or the baryon density. The effect of weakly interacting quarks on the QGP phase diagram are shown and discussed. It is demonstrated that the one-gluon exchange interaction for the massless quarks has considerable effect on the QGP phase diagram and it causes the system to reach to the confined phase at the smaller baryon densities and temperatures. The pressure of excluded volume hadron gas model is also used to find the transition phase diagram. Our results depend on the values of bag pressure and the QCD coupling constant. The latter does not have a dramatic effect on our calculations. Finally, we compare our results with the thermodynamic properties of strange quark matter and the lattice QCD prediction for the QGP transition critical temperature.     

Baryogenesis and neutron-antineutron oscillation at TeV

We propose a TeV extension of the standard model to generate the cosmological baryon asymmetry with an observable neutron-antineutron oscillation. The new fields include a singlet fermion, an isotriplet and two isosinglet diquark scalars. There will be no proton decay although the Majorana mass of the singlet fermion as well as the trilinear couplings between one isosinglet diquark and two isotriplet diquarks softly break the baryon number of two units. The isosinglet diquarks couple to two right-handed down-type quarks or to a right-handed up-type quark and a singlet fermion, whereas the isotriplet diquark couples to two left-handed quarks. The isosinglet diquarks mediate the three-body decays of the singlet fermion to realize a TeV baryogenesis without fine tuning the resonant effect. By the exchange of one singlet fermion and two isosinglet diquarks and of one isosinglet diquark and two isotriplet diquarks, a neutron-antineutron oscillation is allowed to verify in the future experiments.     

Magnetic Effect Versus Thermal Effect on Quark Matter with a Running Coupling at Finite Densities

We investigate the quark matter in a strong magnetic field in the framework of SU(2) NJL model with a magnetic-field-dependent coupling. The spin polarization, the entropy per baryon, and the energy are studied by analyzing the competition of the magnetic effect and the thermal effect. The stronger magnetic field can enhance the spin polarization, arrange quarks in a uniform spin orientation, and change the energy per baryon drastically. However,it can hardly affect the entropy per baryon, which is dominated by the temperature. As the temperature increases, more quarks will be excited from the lowest Landau level up to higher Landau levels.     

Spin Structure of Baryons in Orbiting Valence Quark Model

The quark model with orbital motion of the valence quarks is constructed to reproduce the spin structure of baryons. The relations between the spin-averaged sum rules and baryon magnetic moments found in the previous works do not remain, unless the small orbital magnetic moments are neglected. In particular, when the orbital motion of the valence quarks leads to the small contribution of quark orbit-spin to baryon magnetic moments, the sum rules for polarized nucleon are in agreement with the recent experiment.     

Instanton induced chiral symmetry breaking in extended QCD model

A mechanism for instanton induced chiral symmetry breaking in an extended QCD model (QCD with fundamental scalars) is proposed to describe quarks and gluons inside a baryon. The model Lagrangian that we use has the same symmetry properties as QCD. The scalar fields are shown to develop vacuum expectation values in the instanton background and generate masses for the three generation of quarks. The minimization condition is also used to break the flavour symmetry to make the -quark heavier that the and quarks. Received: 16 August 1996 / Revised version: 15 October 1997 / Published online: 26 February 1998     

Unified origin for baryonic visible matter and antibaryonic dark matter

We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the standard model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced nonthermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.     

Flavour and spin structure of linear baryons

Based on the string picture, we construct a phenomenological model for baryons and study their flavour symmetry, exchange degeneracy pattern and spin structure. Baryons on leading trajectories are assumed to have the configuration of two quarks being attached to the ends of a linear string and the third sitting in the middle, called linear baryons. For such linear baryons, a unitarization scheme can be constructed in a manner similar to the dual unitarity scheme for mesons but without recourse to the $\text{1}\text{N}$ expansion. We find that the interchange interaction of the middle quark with one of the other two quarks at the ends of the string can give rise to a large exchange degeneracy breaking of the baryon spectrum. With this non-planar correction, the model of linear baryons can account for the observed pattern of leading baryon states.     

Sea quark effects in non-topological chiral soliton models and the Nambu-Jona-Lasinio approach

The Nambu-Jona-Lasinio model (NJL) in the chiral invariant SU (2)-sector with scalar couplings is solved numerically in the Hartree approximation (zero boson loop) for baryon number B=1. To this end first the polarized vacuum solution (B=0) is constructed using appropriately parametrized non-dynamic meson fields on the chiral circle. The cut-off Λ is fixed to reproduce the pion decay constant. With this choice a full treatment of the polarized vacuum is shown in second-order gradient expansion to be equivalent to considering kinetic energies of the mesons. Solutions of the NJL model with baryon number B=1 are obtained by adding N_c=3 valence quarks to the full polarized vacuum and subjecting them to the same meson fields. If one adds the valence quarks to the kinetic energy of the mesons the usual chiral soliton model with valence quarks (CSM) is obtained. For both, NJL and CSM, the equilibrium radii of the B=1 solution are evaluated and shown to be rather close to each other. The present approach shows no vacuum instabilities. The resulting radii are different from those of the renormalized one-quark-loop model.     

Quark-Meson Bag Model and Hadron Structure

Based on the assumption that quarks (e.g. up, down quarks) couple with σ, ω and π mesons directly, a quark-meson bag model is-proposed. By adjusting the quark effective mass and quark-meson coupling constants, the nucleon, Δ baryon masses and some observables of proton are calculated.     

A logical explanation for quarks

We construct a quantum logic which generates the usual quark states. It follows from this model that quarks can combine only in quark-antiquark pairs and quark (and antiquark) triples. The ground meson and baryon states are also generated and gluons are discussed.     

Ground state baryon magnetic moments and nucleon axial vector coupling

Ground-state baryon magnetic moments and nucleon axial vector coupling are calculated usingqcd inspired configuration mixing and relativistic corrections. Unlike earlier attempts, we incorporate a natural mass scale for quarks, taken as one third the nucleon mass for up and down quarks, and the strange quark mass suggested by the Lipkin’s sum rule. In the parameter-free non-relativistic limit, we find a fairly good fit, which improves upon including relativistic corrections.     

Baryogenesis at the weak phase transition

The weak phase transition of the hot big bang can produce quarks, leptons and weak bosons which are out of thermal equilibrium. In a simple extension of the standard model it is shown that the reactions following top quark decays can generate the cosmological baryon asymmetry. The top quark mass must be close to 80 GeV and the Higgs boson must be lighter than 1 GeV. This baryogenesis mechanism can be directly tested at e⁺e⁻ and hadron collider by searching for spectacular events containing six or more bottom quarks and a violation of baryon number at the decay vertex of a long lived neutral particle.     

Octet and decuplet magnetic and axial couplings from one-loop self-consistent perturbation theory

Octet and decuplet wave functions, obtained in a recent precision fit to the spectrum using one-loop self-consistent perturbation theory of mesons and gluons interacting with bagged relativistic quarks, are used to evaluate axial couplings and magnetic moments. Results are fully competitive with other models and provide further support to one-loop self-consistent perturbation theory as a useful model of baryon structure.     

Baryogenesis and damping in nonminimal electroweak models

We calculate the baryon asymmetry of the Universe in the standard model of the electroweak theory with CP violation appropriate for simple extensions of the Higgs sector. The propagation of quarks of masses up to about 5 GeV are considered, taking into account the effect of damping rate. We find that the contribution of the b quark can still account for the observed baryon asymmetry to within the theoretical uncertainties of such models.

     

Baryon scattering at high energies: wave function,impact factor,and gluon radiation

The scattering of a baryon consisting of three massive quarks is investigated in the high energy limit of perturbative QCD. A model of a relativistic proton-like wave function, dependent on valence quark longitudinal and transverse momenta and on quark helicities, is proposed, and we derive the baryon impact factors for two, three and four t-channel gluons. We find that the baryonic impact factor can be written as a sum of three pieces: in the first one a subsystem consisting of two of the three quarks behaves very much like the quark–antiquark pair in γ^* scattering, whereas the third quark acts as a spectator. The second term belongs to the odderon, whereas in the third (C-even) piece all three quarks participate in the scattering. This term is new and has no analogue in γ^* scattering. We also study the small x evolution of gluon radiation for each of these three terms. The first term follows the same pattern of gluon radiation as the γ^*-initiated quark–antiquark dipole, and, in particular, it contains the BFKL evolution followed by the 2→4 transition vertex (triple pomeron vertex). The odderon term is described by the standard BKP evolution, and the baryon couples to both known odderon solutions, the Janik–Wosiek solution and the BLV solution. Finally, the t-channel evolution of the third term starts with a three-reggeized gluon state, which then, via a new 3→4 transition vertex, couples to the four-gluon (two-pomeron) state. We briefly discuss a few consequences of these findings, in particular the pattern of unitarization of high energy baryon scattering amplitudes.     

Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.     

带有两个重夸克的重子谱计算中几个困难问题的研究

由两个重夸克和一个轻夸克组成的重子可以看作是一个两体系统.它的两个重夸克组成一个玻色型的双夸克团.利用B–S方程导出了它的轻夸克和重的双夸克之间的等效相互作用势.在利用这种势计算重子质量的过程中,发现有几个困难问题需要深入探讨.它们是:(1)算符排序,(2)由非相对论展开带来的误差,(3)自旋–自旋耦合,(4)在标量双夸克组成的重子态和矢量双夸克组成的重子态之间的混合.本文详细地讨论并适当地处理了这些问题.