258 research outputs found
Nambu-Jona-Lasinio Model Coupled to Constant Electromagnetic Fields in D-Dimension
Critical dynamics of the Nambu-Jona-Lasinio model, coupled to a constant
electromagnetic field in D=2, 3, and 4, is reconsidered from a viewpoint of
infrared behavior and vacuum instability. The latter is associated with
constant electric fields and cannot be avoidable in the nonperturbative
framework obtained through the proper time method. As for magnetic fields, an
infrared cut-off is essential to investigate the critical phenomena. The result
reconfirms the fact that the critical coupling in D=3 and 4 goes to zero even
under an infinitesimal magnetic field. There also shows that a non-vanishing
causes instability. A perturbation with
respect to external fields is adopted to investigate critical quantities, but
the resultant asymptotic expansion excellently matches with the exact value.Comment: 27 pages, 17 figure files, LaTe
Effect of Dynamical SU(2) Gluons to the Gap Equation of Nambu--Jona-Lasinio Model in Constant Background Magnetic Field
In order to estimate the effect of dynamical gluons to chiral condensate, the
gap equation of SU(2) gauged Nambu--Jona-Lasinio model, under a constant
background magnetic field, is investigated up to the two-loop order in 2+1 and
3+1 dimensions. We set up a general formulation allowing both cases of electric
as well as magnetic background field. We rely on the proper time method to
maintain gauge invariance. In 3+1 dimensions chiral symmetry breaking
(SB) is enhanced by gluons even in zero background magnetic field and
becomes much striking as the background field grows larger. In 2+1 dimensions
gluons also enhance SB but whose dependence on the background field is
not simple: dynamical mass is not a monotone function of background field for a
fixed four-fermi coupling.Comment: 20 pages, 5 figure
Opposite field septum magnet system for the separation of charged particle beams
Abstract-The Japan Hadron Facility (JHF) accelerator complex comprises a 50-GeV main synchrotron, a 3-GeV rapid-cycling synchrotron, and a 400-MeV linac. The accelerators provide high-intensity, high-energy proton beams for various scientific fields. These high-intensity, high-energy accelerators, especially the 50-GeV main synchrotron, impose tight demands on the injection/extraction septum magnets for a thin structure, large aperture and high operating field. But to manufacture high field septum magnets on the condition of a large aperture is very difficult because of its extraordinarily strong electromagnetic force due to the self-field. To cope with these tight demands, new design concepts of septa are required. An opposite-field septum magnet system is one of the solutions to realize a thin septa or very high-field septum magnets
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
Dynamical symmetry breaking in the Nambu-Jona-Lasino model with external gravitational and constant electric fields
An investigation of the Nambu-Jona-Lasino model with external constant
electric and weak gravitational fields is carried out in three- and four-
dimensional spacetimes. The effective potential of the composite bifermionic
fields is calculated keeping terms linear in the curvature, while the electric
field effect is treated exactly by means of the proper- time formalism.
A rich dynamical symmetry breaking pattern, accompanied by phase transitions
which are ruled, independently, by both the curvature and the electric field
strength is found. Numerical simulations of the transitions are presented.Comment: 20 pages, LaTeX, 6 .ps-figures, Final version published in "Classical
and Quantum Gravity
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