88 research outputs found
The Chromo-Dielectric Soliton Model: Quark Self Energy and Hadron Bags
The chromo-dielectric soliton model (CDM) is Lorentz- and chirally-invariant.
It has been demonstrated to exhibit dynamical chiral symmetry breaking and
spatial confinement in the locally uniform approximation. We here study the
full nonlocal quark self energy in a color-dielectric medium modeled by a two
parameter Fermi function. Here color confinement is manifest. The self energy
thus obtained is used to calculate quark wave functions in the medium which, in
turn, are used to calculate the nucleon and pion masses in the one gluon
exchange approximation. The nucleon mass is fixed to its empirical value using
scaling arguments; the pion mass (for massless current quarks) turns out to be
small but non-zero, depending on the model parameters.Comment: 24 pages, figures available from the author
Hadronization of a Quark-Gluon Plasma in the Chromodielectric Model
We have carried out simulations of the hadronization of a hot, ideal but
effectively massive quark-gluon gas into color neutral clusters in the
framework of the semi-classical SU(3) chromodielectric model. We have studied
the possible quark-gluon compositions of clusters as well as the final mass
distribution and spectra, aiming to obtain an insight into relations between
hadronic spectral properties and the confinement mechanism in this model.Comment: 34 pages, 37 figure
ROBO: a Model and a Code for the Study of the Interstellar Medium
We present ROBO, a model and its companion code for the study of the
interstellar medium (ISM). The aim is to provide an accurate description of the
physical evolution of the ISM and to set the ground for an ancillary tool to be
inserted in NBody-Tree-SPH (NB-TSPH) simulations of large scale structures in
cosmological context or of the formation and evolution of individual galaxies.
The ISM model consists of gas and dust. The gas chemical composition is
regulated by a network of reactions that includes a large number of species
(hydrogen and deuterium based molecules, helium, and metals). New reaction
rates for the charge transfer in and collisions are
presented. The dust contains the standard mixture of carbonaceous grains
(graphite grains and PAHs) and silicates of which the model follows the
formation and destruction by several processes. The model takes into account an
accurate treatment of the cooling process, based on several physical
mechanisms, and cooling functions recently reported in the literature. The
model is applied to a wide range of the input parameters and the results for
important quantities describing the physical state of the gas and dust are
presented. The results are organized in a database suited to the artificial
neural networks (ANNs). Once trained, the ANNs yield the same results obtained
by ROBO, with great accuracy. We plan to develop ANNs suitably tailored for
applications to NB-TSPH simulations of cosmological structures and/or galaxies.Comment: accepted for publication in section 15. Numerical methods and codes
of Astronomy and Astrophysic
Graphene on hexagonal boron nitride as a tunable hyperbolic metamaterial
Hexagonal boron nitride (h-BN) is a natural hyperbolic material1, in which the dielectric constants are the same in the basal plane (Δ[superscript t]ââĄâΔ[superscript x]â=âΔ[superscript y]) but have opposite signs (Δ[superscript t] Δ[superscript zâ]<â0) in the normal plane (Δ[superscript z]). Owing to this property, finite-thickness slabs of h-BN act as multimode waveguides for the propagation of hyperbolic phonon polaritonsâcollective modes that originate from the coupling between photons and electric dipoles in phonons. However, control of these hyperbolic phonon polaritons modes has remained challenging, mostly because their electrodynamic properties are dictated by the crystal lattice of h-BN. Here we show, by direct nano-infrared imaging, that these hyperbolic polaritons can be effectively modulated in a van der Waals heterostructure composed of monolayer graphene on h-BN. Tunability originates from the hybridization of surface plasmon polaritons in graphene with hyperbolic phonon polaritons in h-BN so that the eigenmodes of the graphene/h-BN heterostructure are hyperbolic plasmonâphonon polaritons. The hyperbolic plasmonâphonon polaritons in graphene/h-BN suffer little from ohmic losses, making their propagation length 1.5â2.0 times greater than that of hyperbolic phonon polaritons in h-BN. The hyperbolic plasmonâphonon polaritons possess the combined virtues of surface plasmon polaritons in graphene and hyperbolic phonon polaritons in h-BN. Therefore, graphene/h-BN can be classified as an electromagnetic metamaterial as the resulting properties of these devices are not present in its constituent elements alone
REAL-TIME DESCRIPTION OF PARTON-HADRON CONVERSION AND CONFINEMENT DYNAMICS
We propose a new and universal approach to the hadronization problem that
incorporates both partonic and hadronic degrees of freedom in their respective
domains of relevance, and that describes the conversion between them within a
kinetic field theory formulation in real time and full 7-dimensional phase
space. We construct a scale-dependent effective theory that reduces to
perturbative QCD with its scale and chiral symmetry properties at short
space-time distances, but at large distances (r > 1 fm) yields symmetry
breaking gluon and quark condensates plus hadronic excitations. The approach is
applied to the evolution of fragmenting qq~ and gg jet pairs as the system
evolves from the initial 2-jet configuration, via parton showering and cluster
formation, to the final yield of hadrons. The phenomenological implications for
e+e- -> hadrons are investigated, such as the time scale of the transition, and
its energy dependence, cluster size and mass distributions. We compare our
results for particle production and Bose-Einstein correlations with
experimental data, and find an interesting possibility of extracting the basic
parameters of the space-time evolution of the system from Bose enhancement
measurements.Comment: 51 pages, latex, 14 figures as uu-encoded postscript file
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