3 research outputs found

    Hybrid Baryons in Large-N_c QCD

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    We study the properties and couplings of hybrid baryons in the large-NcN_c expansion. These are color-neutral baryon states which contain in addition to NcN_c quarks also one constituent gluon. Hybrid baryons with both symmetric and mixed symmetric orbital wave functions are considered. We introduce a Hartree description for these states, similar to the one used by Witten for ordinary baryons. It is shown that the Hartree equations for Nc(Nc−1)N_c (N_c-1) quarks for symmetric (mixed symmetric) states in these states coincide with those in ordinary baryons in the large-NcN_c limit. The energy due to the gluon field is of order ΛQCD\Lambda_{QCD}. Under the assumption of color confinement, our results prove the existence of hybrid baryons made up of heavy quarks in the large NcN_c limit and provides a justification for the constituent gluon picture of these states. The couplings of the hybrid baryons to mesons of arbitrary spin are computed in the quark model. Using constraints from the large NcN_c scaling laws for the meson-baryon scattering amplitudes, we write down consistency conditions for the meson couplings of the hybrid baryons. These consistency conditions are solved explicitly with results in agreement with those in the quark model for the respective couplings.Comment: 20 pages and one figure, ReVTe

    Dynamics of Baryons from String Theory and Vector Dominance

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    We consider a holographic model of QCD from string theory, a la Sakai and Sugimoto, and study baryons. In this model, mesons are collectively realized as a five-dimensional \U(NF)=U(1)×SU(NF)U(N_F)=U(1)\times SU(N_F) Yang-Mills field and baryons are classically identified as SU(NF)SU(N_F) solitons with a unit Pontryagin number and NcN_c electric charges. The soliton is shown to be very small in the large 't Hooft coupling limit, allowing us to introduce an effective field B{\cal B}. Its coupling to the mesons are dictated by the soliton structure, and consists of a direct magnetic coupling to the SU(NF)SU(N_F) field strength as well as a minimal coupling to the U(NF)U(N_F) gauge field. Upon the dimensional reduction, this effective action reproduces all interaction terms between nucleons and an infinite tower of mesons in a manner consistent with the large NcN_c expansion. We further find that all electromagnetic interactions, as inferred from the same effective action via a holographic prescription, are mediated by an infinite tower of vector mesons, rendering the baryon electromagnetic form factors completely vector-dominated as well. We estimate nucleon-meson couplings and also the anomalous magnetic moments, which compare well with nature.Comment: 65pages, 3 figures, vector mesons and axial-vector mesons are now canonically normalized (comparisons with data and conclusions unaffected

    Phenomenological Review on Quark-Gluon Plasma: Concepts vs. Observations

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    In this review, we present an up-to-date phenomenological summary of research developments in the physics of the Quark--Gluon Plasma (QGP). A short historical perspective and theoretical motivation for this rapidly developing field of contemporary particle physics is provided. In addition, we introduce and discuss the role of the quantum chromodynamics (QCD) ground state, non-perturbative and lattice QCD results on the QGP properties, as well as the transport models used to make a connection between theory and experiment. The experimental part presents the selected results on bulk observables, hard and penetrating probes obtained in the ultra-relativistic heavy-ion experiments carried out at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (BNL RHIC) and CERN Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) accelerators. We also give a brief overview of new developments related to the ongoing searches of the QCD critical point and to the collectivity in small (p+pp+p and p+Ap+A) systems.Comment: 64 pages, 29 figures; a new subsection 4.4.2 and a few references have been added; minor changes; published versio
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