Renormalized QCD-inspired model for the pion and mesons

We apply the subtraction method to an effective QCD-inspired model, which includes the Coulomb plus a zero-range hyperfine interactions, to define a renormalized Hamiltonian for mesons. The spectrum of the renormalized Hamiltonian agrees with the one obtained with a smeared hyperfine interaction. The masses of the low-lying pseudo scalar and vector mesons are reasonably described within the model.Comment: 5 pages, 3 figures, 5 references. To be published in Nucl. Phys. B (Proc. Suppl.) Talk presented at the Workshop "Light-cone Physics: Particles and Strings" at ECT* in Trento, Sep 3-11, 200

Light-Front Bethe-Salpeter Equation

A three-dimensional reduction of the two-particle Bethe-Salpeter equation is proposed. The proposed reduction is in the framework of light-front dynamics. It yields auxiliary quantities for the transition matrix and the bound state. The arising effective interaction can be perturbatively expanded according to the number of particles exchanged at a given light-front time. An example suggests that the convergence of the expansion is rapid. This result is particular for light-front dynamics. The covariant results of the Bethe-Salpeter equation can be recovered from the corresponding auxiliary three-dimensional ones. The technical procedure is developed for a two-boson case; the idea for an extension to fermions is given. The technical procedure appears quite practicable, possibly allowing one to go beyond the ladder approximation for the solution of the Bethe-Salpeter equation. The relation between the three-dimensional light-front reduction of the field-theoretic Bethe-Salpeter equation and a corresponding quantum-mechanical description is discussed.Comment: 42 pages, 5 figure

Evaluation of current density on the surface of the left atrium during TAS

Conditions for the indirect transesophageal atrial stimulation (TAS), useful for cardiac diagnosis and treatment, are optimized both by way of clinical experiment and a computer modelling. The paper demonstrates the results of comparison of electric current density, obtained on the surface of the left atrium during computer modelling, with the results of our own experiments. An evaluation was made with the use of spiral CT scanning of the distance between the esophagus and the posterior wall of the left atrium. The average distance in the tested group of 27 subjects was 4.7 ±σ = 1.1 mm. During transesophageal stimulation, we have determined the average excitation threshold of the left atrium, obtaining the value 5.5 ±σ = 1.8 mA in the examined group of 27 patients. The calculated average current density on the surface of left atrium for the selective electrode with point poles used in the experiment amounted to 39.6 μA/mm2. Electric current densities obtained by other researchers by means of computer modelling for omnidirectional and selective ring electrodes turned out to be much lower after adjustment to similar conditions, which was the result of electrically active larger sizes surfaces of the poles of electrodes used in the modelling