A possible description of baryon dynamics in dual and gauge theories

We present an attempt to generalize to baryons a framework recently proposed in order to unify gauge, dual and Regge-Gribov theories of mesons. We find it necessary to depart from the $\text{1}\text{N}{}_{\mathrm{<mtext>colour</mtext>}}$ expansion of quantum chromodynamics (QCD) and to replace it by a more general definition of a “dual” approximation of QCD, based on the zero-width limit. Theoretical and phenomenological consequences of the scheme are derived. For N_colour = 3, the baryon resembles a Y shaped string; three families of new “baryonium” bound states are predicted and rough estimates of intercepts and slopes of the associated Regge trajectories are given. A new type of Zweig-like selection rule is found to hold in leading order and its violations through higher-order topologies are discussed. Duality diagrams for baryons are ambiguous unless implemented with extra lines indicating the flow of certain colour indices. Duality between scattering and annihilation channels is found in B$\text{B}$ scattering and its consequences are discussed. Some justification is given for the quark counting rule for total cross sections. Finally, implications of our scheme for the Regge-Gribov calculus in processes involving baryons are discussed.     

One-loop corrections to the baryon axial vector current

The symmetry breaking corrections to the pion?Cbaryon couplings vanish to first order in 1/N _c, where N _c is the number of colours. Loop graphs with octet and decuplet intermediate states cancel to various orders in N _c as a consequence of the large-N _c spin-flavour symmetry of QCD baryons. The baryon axial vector current is computed at one-loop order in heavy baryon chiral perturbation theory in the large N _c limit. 1/N _c corrections in the case of g _A in QCD are presented here.     

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.     

Baryons in the effective lagrangian of strongly coupled lattice QCD

The effective action formulation of lattice QCD is extended to incorporate baryons. At strong coupling we find a generalized σ model where the baryons obtain their mass via a non-vanishing vacuum expectation value 〈¯ΦΦ〉. The SU(3) effective potential is worked out for Susskind fermions taking into account the influence of the baryons, and the results are compared with the U(3) theory. The large-N behavior of the SU(N) theory is studied as well. A loop expansion method is proposed for dealing with general multi-component baryon fields in both Susskind's and Wilson's fermion formulations.     

Baryon production in lepton-nucleon scattering and diquark fragmentation

We study baryon production in deep inelastic scattering using an extended version of the Lund jet model. There are two contributing sources. The first is baryon production in the target fragmentation. In a scheme related to our earlier work on lowp _hu baryon fragmentation we present some details of the fragmentation of a diquark into baryons and mesons. A non-negligible baryon-antibaryon production is observed ine ⁺ e ^? annihilation. In a previous paper we developed a model for this production, and the same mechanism should also give fast baryons in leptoproduction. In this paper we discuss those features of baryon production which can be more easily studied in a leptoproduction experiment.     

1/<Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> countings in baryons

The 1/N _c -power countings for baryon decays and configuration mixings are determined by means of a nonrelativistic quark picture. Such countings are expected to be robust under changes in the quark masses and, therefore, valid as these become light. It is shown that excited baryons have natural widths of \(\mathcal{O}(N_c^0 )\). These dominant widths are due to the decays that proceed directly to the ground-state baryons, with cascade decays being suppressed to \(\mathcal{O}(1/N_c )\). Configuration mixings, defined as mixings between states belonging to different O(3) × SU(2N _f ) multiplets, are shown to be subleading in an expansion in \(1/\sqrt {N_c }\) when they involve the ground-state baryons, while the mixings between excited states can be \(\mathcal{O}(N_c^0 )\).     

The development of baryon asymmetry in the early universe

The development of an excess of baryons over antibaryons due to CP and baryon number violating reactions during the very early stages of the big bang is calculated in simple models using the Boltzmann equation. We show that it is necessary to solve the coupled Boltzmann equations in order to determine the final baryon number in any specific model.     

Baryon exchange effects in dual unitarisation

The effects of baryon exchanges in the renormalisation of Regge trajectories are studied in the dual unitarisation scheme. The main results are that: (i) the pomeron is boosted above α = 1, giving rising total cross sections beyond baryon-antibaryon thresholds, and (ii) the ω trajectory remains approximately at α = 0.5 but acquires a sizeable admixture of the exotic $\text{q}\text{q}\text{qq}$ state, which enhances its coupling to baryons. There are in addition a number of other interesting predictions.     

Searches for exotic baryons of isospin 5/2 that consist of light quarks

The status of isospin-5/2 exotic baryons consisting of light-quarks is considered. A brief survey of theoretical studies devoted to them is given. Experimental searches for exotic baryons are traced from the first publication on the subject to the present day. Among possible candidates for an exotic baryon, the pentaquark baryon E _{5/2 5/2} of mass M ≈ 1.44 GeV/c ² and width Γ < 0.05 GeV/c ² is the most probable. This state was recorded in six studies at five different facilities. Among these, there are two studies where the excess of the signal above the background is more than five standard deviations. The possibility of further searches for exotic baryons in various reactions is discussed.     

Decays of excited baryons in the large- N<Subscript>c</Subscript> expansion of QCD

We present the analysis of the decay widths of excited baryons in the framework of the 1/N _c expansion of QCD. These studies are performed up to order 1/N _c and include both positive- and negative-parity excited baryons.     

On the nature of the lowest 1/2<Superscript>-</Superscript> baryon nonet and decuplet<Superscript>⋆</Superscript>

From our recent study of properties of the lowest spin-parity 1/2^- baryons, N ^*(1535) and Δ^*(1620) , new pictures for the internal structure of the lowest 1/2^- baryon nonet and decuplet are proposed. While the lowest 1/2^- baryon nonet may have large diquark-diquark-antiquark component, the lowest 1/2^- baryon decuplet is proposed to have large vector-meson-baryon components. Evidence for “missing" members of the new pictures is pointed out and suggestions are made for detecting these predicted states from forthcoming experiments.     

Baryons in dual unitarization and dynamical thresholds

Baryon exchange and baryon resonance production is introduced in the dual unitarisation scheme. The dynamical threshold for the production of meson and baryon resonances is incorporated. It is shown that the intercepts of the ω and the f, which are generated by baryons, are suppressed by the above dynamical threshold effects to $\text{α}{}_{\mathrm{\omega }}\text{(0) ? 0}$ and α_f(0) < 0. The pomeron is shifted slightly upwards by baryon production. An upper limit is determined for the ratio of the crossed and uncrossed produced baryon lines. The breaking of the Freund-Rosner-Walz rule is discussed.     

Topological bootstrap theory of hadrons

A topological framework is constructed for anS-matrix bootstrap theory of particles. Each component of anS-matrix topological expansion is associated with a pair of intersecting “quantum” and “classical” surfaces whose complexity exhibits an entropy property. The bounded classical surface embeds graphs that carry the direct observables — energymomentum, spin and electric charge. The closed quantum surface carries a triangulation whose orientations represent internal quantum numbers — which turn out to be baryon number, lepton number and flavor. A form of “color” automatically appears. All strong-interaction components of the expansion are generated through “Landau connected sums” from “zeroentropy” surface pairs — which are self generating. Elementary particles correspond to triangulated areas on the quantum surface; consistency at zero entropy determines allowed hadrondisks on quantum spheres together with the associated quantum numbers. Elementary topological hadrons turn out to include mesons, baryons and baryoniums, with quarks appearing as “peripheral triangles” (along the perimenters of hadron disks) whose attachments correspond to a total of 8 flavors as well as spin. Individual quarks do not carry momentum and cannot be hadrons; quark confinement is automatic. Also appearing within hadron disks are “core triangles” that carry baryon number and electric charge but no flavor or spin. Hadron disks have quantum numbers that accord with the lowestmass physically-observed mesons and baryons. The relation of topological theory to QCD is discussed.     

Model independent relations for baryons as solitons in mesonic theories

We derive model-independent relations for SU(2) and SU(3) chiral solitons. These relations depend only on the soliton picture of baryons and therefore are a test of the 1/N expansion. In the two-flavor case we discuss the magnetic moment and the electric quadrupole transition of the Δ. In SU(3) we discuss magnetic moments, including SU(3) breaking effects and 1/N corrections.     

Bound-state approach to strangeness in the Skyrme model

We show that baryons carrying heavy flavors, such as strangeness and charm, can be described by bound states of the corresponding heavy mesons in the background field of the basic SU(2) skyrmion. This method is quantitatively successful to O(N_c⁰), in the sense of the large-N_c expansion, but at O(1/N_c) it experiences problems associated with our lack of knowledge of higher-derivative terms in the Skyrme action. We derive a model-independent mass relation for strange baryons which is in excellent agreement with experiment.     

Octet-decuplet baryon mass splittings from self-consistent one-loop perturbation theory

The bag model of confined relativistic quarks in chiral-invariant interaction with scalar, pseudoscalar, vector, and pseudovector mesons, as well as gluons, is used to calculate the masses and wave functions of the spin-1/2 baryon octet and spin-3/2 decuplet, using selfconsistent Brillouin-Wigner bound state perturbation theory. Chiral symmetry breaking is invoked with the sigma model. SU (6) and SU (3) symmetries are broken by the experimental meson spectrum, and a strange quark mass. Mass corrections are calculated to one loop order, limited to the baryons of the octet and decuplet and the lowest lying mesons. Encouraging results are obtained, especially for theΔ — N and theΣ — Λ splittings. Convergence and stability have not been demonstrated, but are evidently improved by the self-consistency requirement. An initial parameter tuning gives a fit to all the octet and decuplet masses within ≦0.02 GeV, at the price of choosing the bag radius, the non-strange baryon input bag mass, and the strange quark mass. Even these small discrepancies can be dramatically reduced by fine-tuning the vector meson coupling and including an instanton contribution peculiar to theΛ.     

Heavy to light baryon weak form factors in the lightcone constituent quark model

Heavy to light baryon weak form factors are investigated in a lightcone constituent quark model. In a SU(4) symmetry broken scheme, both charged and neutral weak current-induced form factors are calculated at theq ² = 0 point including the leading relativistic effects in the spin composition of baryons. The corresponding semileptonic decays are described by assuming dipole dependence of form factors onq ².