451 research outputs found
Inhomogeneous phase of a Gluon Plasma at finite temperature and density
By considering the non-perturbative effects associated with the fundamental
modular region, a new phase of a Gluon Plasma at finite density is proposed. It
corresponds to the transition from glueballs to non-perturbative gluons which
condense at a non vanishing momentum. In this respect the proposed phase is
analogous to the color superconducting LOFF phase for fermionic systems.Comment: 5 pages, 2 figure
Electron cloud buildup and impedance effects on beam dynamics in the future circular e+eâ collider and experimental characterization of thin TiZrV vacuum chamber coatings
The Future Circular Collider FCC-ee is a study toward a high luminosity electron-positron collider with a centre-of-mass energy from 91 GeV to 365 GeV. Due to the beam parameters and pipe dimensions, collective effects and electron cloud can be very critical aspects for the machine and can represent the main limitations to its performance. An estimation of the electron cloud build up in the main machine components and an impedance model are required to analyze the induced instabilities and to find solutions for their mitigation. Special attention has been given to the resistive wall impedance associated with a layer of nonevaporable getter (NEG) coating on the vacuum chamber required for electron cloud mitigation. The studies presented in this paper will show that minimizing the thickness of this coating layer is mandatory to increase the single bunch instability thresholds in the proposed lepton collider at 45.6 GeV. For this reason, NEG thin films with thicknesses below 250 nm have been investigated by means of numerical simulations to minimize the resistive wall impedance. In parallel, an extensive measurement campaign was performed at CERN to characterize these thin films, with the purpose of finding the minimum effective thickness satisfying vacuum and electron cloud requirements
Polyakov Loop and Gluon Quasiparticles in Yang-Mills Thermodynamics
We study the interpretation of Lattice data about the thermodynamics of the
deconfinement phase of SU(3) Yang-Mills theory, in terms of gluon
quasiparticles propagating in a background of a Polyakov loop. A potential for
the Polyakov loop, inspired by the strong coupling expansion of the QCD action,
is introduced; the Polyakov loop is coupled to tranverse gluon quasiparticles
by means of a gas-like effective potential. This study is useful to identify
the effective degrees of freedom propagating in the gluon medium above the
critical temperature. A main general finding is that a dominant part of the
phase transition dynamics is accounted for by the Polyakov loop dynamics, hence
the thermodynamics can be described without the need for diverging or
exponentially increasing quasiparticle masses as , at
variance respect to standard quasiparticle models.Comment: 8 pages, 9 figure
Trace Anomaly and Quasi-Particles in Finite Temperature SU(N) Gauge Theory
We consider deconfined matter in SU(N) gauge theory as an ideal gas of
transversely polarized quasi-particle modes having a temperature-dependent mass
m(T). Just above the transition temperature, the mass is assumed to be
determined by the critical behavior of the energy density and the screening
length in the medium. At high temperature, it becomes proportional to T as the
only remaining scale. The resulting (trace anomaly based) interaction measure
Delta=(e - 3P)/T^4 and energy density are found to agree well with finite
temperature SU(3) lattice calculations.Comment: 13 pages, 13 figures; references added for version
Moments of the Virtual Photon Structure Function
The photon structure function is a useful testing ground for QCD. It is
perturbatively computable apart from a contribution from what is usually called
the hadronic component of the photon. There have been many proposals for this
nonperturbative part of the real photon structure function. By studying moments
of the virtual photon structure function, we explore the extent to which these
proposed nonperturbative contributions can be identified experimentally.Comment: LaTeX, 16 pages + 14 compressed and uuencoded postscript figures,
UMN-TH-1111/9
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