scholarly journals 4He(γ,d)dand3He(γ,p)dreactions in nonlocal covariant model

2014 ◽  
Vol 66 ◽  
pp. 03040
Author(s):  
Yu. A. Kasatkin ◽  
P.E. Kuznietsov ◽  
O.E. Koshchii ◽  
V.F. Klepikov
Keyword(s):  
Covariant Model

scholarly journals Studying time-like electromagnetic baryonic transitions with HADES in pion induced reactions

2020 ◽  
Vol 241 ◽  
pp. 01012
Author(s):  
Béatrice Ramstein
Keyword(s):  
Center Of Mass ◽  
Quantitative Description ◽  
Form Factors ◽  
Resonance Region ◽  
Partial Wave Analysis ◽  
Real Photon ◽  
Pion Beam ◽  
Dalitz Decay ◽  
Covariant Model ◽  
Proton Induced Reactions

A dedicated programme aiming at studying electromagnetic baryonic transitions in the time-like region has started at GSI using the pion beam and the High Acceptance Di-Electron Spectrometer (HADES) set-up. A pioneering experiment has been carried out in the second resonance region, at a center-of-mass energy of 1.49 GeV, using carbon and polyethylene targets, allowing for an analysis of the inclusive e+e- production and of the exclusive quasi-free π-p → ne+e- reaction, in complement to hadronic channels. Predictions for the Dalitz decay of N(1520) and N(1535) based on real photon couplings strongly underestimate the e+e- yield at invariant masses larger than 300 MeV/c2, which signals effects of time-like baryon transition form factors, in qualitative agreement with the Vector Dominance Models (VDM). A quantitative description of the observed e+e- yield is achieved by taking into account the contribution from off-shell ρs. The latter was provided by the preliminary results of a Bonn-Gatchina Partial Wave Analysis of the two-pion production channels, which were measured simultaneously in our experiment. A good agreement is also obtained using a covariant model for the time-like electromagnetic form factors for the N-N(1520) transition. The angular distributions for the e+e- production contain additional selective information on the spin structure of the different transitions. The measurements with the pion beam will be extended in future in the third resonance region. Hyperon Dalitz decay studies in proton induced reactions are also foreseen.

scholarly journals A covariant model for the γ∗N→N∗(1520) reaction

2014 ◽  
Vol 73 ◽  
pp. 04018
Author(s):  
G. Ramalho ◽  
M.T. Peña
Keyword(s):  
Covariant Model

scholarly journals RADIATIVE DAMPING AND FUNCTIONAL DIFFERENTIAL EQUATIONS

2011 ◽  
Vol 26 (35) ◽  
pp. 2627-2638 ◽  
Author(s):  
SUVRAT RAJU ◽  
C. K. RAJU
Keyword(s):  
Differential Equations ◽  
Body Problem ◽  
Equations Of Motion ◽  
Functional Differential Equations ◽  
General Technique ◽  
Covariant Model ◽  
Maxwell Electrodynamics ◽  
Functional Differential ◽  
The One ◽  
Radiative Damping

We propose a general technique to solve the classical many-body problem with radiative damping. We modify the short-distance structure of Maxwell electrodynamics. This allows us to avoid runaway solutions as if we had a covariant model of extended particles. The resulting equations of motion are functional differential equations (FDEs) rather than ordinary differential equations (ODEs). Using recently developed numerical techniques for stiff, retarded FDEs, we solve these equations for the one-body central force problem with radiative damping. Our results indicate that locally the magnitude of radiation damping may be well approximated by the standard third-order expression but the global properties of our solutions are dramatically different. We comment on the two-body problem and applications to quantum field theory and quantum mechanics.

The Lorentz covariant Lee model

1963 ◽  
Vol 271 (1346) ◽  
pp. 332-356 ◽  
Keyword(s):  
Configuration Space ◽  
Complete Solution ◽  
Point Interaction ◽  
Interacting Particles ◽  
Covariant Model ◽  
Reliable Procedure ◽  
Set Up ◽  
Physical Consequences ◽  
Renormalization Method ◽  
Three Space

A quantum theory of interacting particles with rigorous Lorentz covariance and rigorous conservation laws of Lee type is set up; the process A ↔ B 1 + B 2 is permitted via a point interaction. For simplicity the particles are assumed to be scalars. The complete solution of the lowest `sector ’ of interest is straightforward in configuration space for the case of one space dimension. It is in the case of three space dimensions that the usual difficulties associated with a point interaction arise; it is shown that the use of a cut-off is not a reliable procedure in this context, and a section of the paper is devoted to the development of a device for dealing with these difficulties which differs from the usual renormalization method. It is found that applying this device to the covariant model leads to a theory which is without infinite renormalization of any kind, and which admits a legitimate ‘physical’ in terpretation after certain necessary ‘supplementary conditions’ are applied. The S -states in the lowest sector are fully described in configuration space. Finally, an indication of the variety of different models which may be obtained is given, and it is found that certain models which are at first sight unacceptable on account of their structure in the absence of interaction lead in fact to ‘physical’ consequences which are perfectly satisfactory.

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