Search results for "quantum electrodynamics"
showing 10 items of 809 documents
On the (ΔΔ)-component of the deuteron
1974
Abstract The (ΔΔ)-component of the deuteron is investigated using π- and ϱ-exchange for the (NN → ΔΔ)-transition interaction. The depedence of the strength of the (ΔΔ)-component on thetype of regularization, the cut-off parameter and the normal deuteron wave functions is discussed. Inclusion of the ϱ-exchange leads to a weaker dependence on the cut-off parameter and to a smaller (ΔΔ)-admixture probability of 0.7 to 1.2 percent depending on the normal deuteron wave function for a cut-off parameter Λ = 5 fm−1.
Magnetic moment of the S11 (1535) resonance
2003
Abstract The γ p a γη p reaction in the S 11 (1535) resonance region is investigated as a method to access the S 11 (1535) magnetic dipole moment. To study the feasibility, we perform calculations of the γ p → γη p process within an effective Lagrangian approach containing both the S 11 resonant mecanism and a background of non-resonant contributions. Predictions are made for the forthcoming experiments. In particular, we focus on the sensitivity of cross sections and photon asymmetries to the S 11 (1535) magnetic dipole moment.
High temperature giant dipole and isoscalar resonances
1990
We present a systematic study of the Giant Dipole Resonance (GDR) at high temperatures (T≧4 MeV) in the framework of a semiclassical approximation that uses them1 andm3 RPA sum rules to estimate the GDR mean energy. We focus on the evolution withT of the collective nature of the GDR and of theL=0, 2, 3 and 4 isoscalar resonances. We find that the GDR remains particularly collective at highT, suggesting that it might be possible to observe it experimentally even at temperatures close to the maximum one a nucleus can sustain.
Multiparticle correlations in the Schwinger mechanism
2009
We discuss the Schwinger mechanism in scalar QED and derive the multiplicity distribution of particles created under an external electric field using the LSZ reduction formula. Assuming that the electric field is spatially homogeneous, we find that the particles of different momenta are produced independently, and that the multiplicity distribution in one mode follows a Bose-Einstein distribution. We confirm the consistency of our results with an intuitive derivation by means of the Bogoliubov transformation on creation and annihilation operators. Finally we revisit a known solvable example of time-dependent electric fields to present exact and explicit expressions for demonstration.
Electromagnetic transition form factors of the Roper resonance in a phenomenological field theory
2014
We analyze the form factors of the electromagnetic nucleon-to-Roper-resonance transition in the framework of a low-energy phenomenological field theory. A systematic power-counting procedure is generated by applying the complex-mass scheme. Within this power counting we calculate the form factors to next-to-next-to-leading order and fit the results to empirical data.
Equation of state of strongly interacting matter and intensity interferometry of thermal photons
2011
Abstract We find that an equation of state (EOS) for hot hadronic matter consisting of all mesons (baryons) having M 1.5 ( 2.0 ) GeV along with Hagedorn resonances in thermal and chemical equilibrium, matches rather smoothly with lattice EOS ( p 4 action, N τ = 8 ) for T up to ≈200 MeV, when corrections are made for the finite volume of hadrons. Two equations of state, HHL and HHB are constructed where the above is matched to the lattice and bag model EoS respectively at a critical temperature T c = 165 MeV . We find that the particle and thermal photon spectra differ only marginally for the two equations of state at both RHIC and LHC energies. The intensity interferometry results, speciall…
Chiral unitary approach to the K^- deuteron scattering length
2000
Starting from a recent model where the Kbar N amplitudes are evaluated from the chiral Lagrangians using a coupled channel unitary method, we evaluate here the scattering length for K^- deuteron scattering. We find that the double scattering contribution is very large compared to the impulse approximation and that the charge exchange contribution of this rescattering is as large as the sequential K^- scattering on the two nucleons. Higher order rescattering corrections are evaluated using coupled channels with K^- and Kbar^0 within the integral form of the fixed centre approximation to the Faddeev equations. The higher order corrections involving intermediate pions and hyperons are found ne…
Relativistic approach to positronium levels in a strong magnetic field
2001
We have investigated the bound states of an electron and positron in superstrong magnetic fields typical for neutron stars. The complete relativistic problem of positronium in a strong magnetic field has not been succesfully solved up to now. In particular, we have studied the positronium when it moves relativistically across the magnetic field. A number of problems which deal with the pulsar magnetosphere, as well as the evolution of protoneutron stars, could be considered as a field for application.
Finite-size Scaling of Meson Propagators
2001
Using quenched chiral perturbation theory we compute meson correlation functions at finite volume and fixed gauge field topology. We also present the corresponding analytical predictions for the unquenched theory at fixed gauge field topology. These results can be used to measure the low-energy parameters of the chiral Langrangian from lattice simulations in volumes much smaller than one pion Compton wavelength.
Description of sub-barrier heavy ion fusion in a semiclassical quantum tunneling model
1996
In this paper we apply the semiclassical method based on the Feynman path integral formalism to sub-barrier fusion of heavy nuclei. Cross sections are calculated and compared to experimental data and to coupled-channel calculations for different mass systems: 32S124Mg, 58Ni164Ni, and 16O1208Pb. The semiclassical method and coupled-channel calculations give comparable results. It is found that the coupling produces a renormalization of the barrier that is responsible for the enhancement of sub-barrier fusion cross sections and a dissipative force along the classical tunneling path.