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 $F_{\mu\nu}\widetilde F^{\mu\nu}$ 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 ($\chi$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 $\chi$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

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

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

SUBARU IMAGING OF ASYMMETRIC FEATURES IN A TRANSITIONAL DISK IN UPPER SCORPIUS

We report high-resolution (0.07 arcsec) near-infrared polarized intensity imagesof the circumstellar disk around the star 2MASS J16042165-2130284 obtainedwith HiCIAO mounted on the Subaru 8.2 m telescope. We present ourH-band data, which clearly exhibits a resolved, face-on disk with a large innerhole for the first time at infrared wavelengths. We detect the centrosymmetricpolarization pattern in the circumstellar material as has been observed in otherdisks. Elliptical fitting gives the semimajor axis, semiminor axis, and positionangle (P.A.) of the disk as 63 AU, 62 AU, and -14 ◦, respectively. The disk isasymmetric, with one dip located at P.A.s of 85◦. Our observed disk size agreeswell with a previous study of dust and CO emission at submillimeter wavelengthwith Submillimeter Array. Hence, the near-infrared light is interpreted as scatteredlight reflected from the inner edge of the disk. Our observations also detectan elongated arc (50 AU) extending over the disk inner hole. It emanates at theinner edge of the western side of the disk, extending inward first, then curving tothe northeast. We discuss the possibility that the inner hole, the dip, and the arcthat we have observed may be related to the existence of unseen bodies withinthe disk