3 research outputs found
Hybrid Baryons in Large-N_c QCD
We study the properties and couplings of hybrid baryons in the large-
expansion. These are color-neutral baryon states which contain in addition to
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 quarks for
symmetric (mixed symmetric) states in these states coincide with those in
ordinary baryons in the large- limit. The energy due to the gluon field is
of order . Under the assumption of color confinement, our
results prove the existence of hybrid baryons made up of heavy quarks in the
large 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 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
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 \ Yang-Mills field and baryons
are classically identified as solitons with a unit Pontryagin number
and electric charges. The soliton is shown to be very small in the large
't Hooft coupling limit, allowing us to introduce an effective field . Its coupling to the mesons are dictated by the soliton structure, and
consists of a direct magnetic coupling to the field strength as well
as a minimal coupling to the 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
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
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 ( and ) systems.Comment: 64 pages, 29 figures; a new subsection 4.4.2 and a few references
have been added; minor changes; published versio