Search results for "quantum electrodynamics"
showing 10 items of 809 documents
Elements of Quantum Electrodynamics and Weak Interactions
2013
Quantum field theory in its application to electroweak and strong interactions has two rather different facets: A pragmatic, empirical one, and an algebraic, systematical one. The pragmatic approach consists in a set of rules and formal calculational procedures which are extremely successful in their application to concrete physical processes, but rest on mathematically shaky ground. The mathematically rigorous approach, in turn, is technically difficult and not very useful, from a practical point of view, for reaching results which can be compared with phenomenology. Generally speaking, quantum field theory quickly becomes rather technical if one wants to understand it in some depth, and g…
Critical behavior with dramatic enhancement of modulational instability gain in fiber systems with periodic variation dispersion
2008
International audience; We analyze modulational instability (MI) of light waves in fiber systems with periodically varying dispersion. The dispersion fluctuation generates special waves, called nonconventional MI sidebands, which are shown to be highly sensitive to two fundamental system parameters. The first one is the average dispersion of the system. Surprisingly, the second parameter turns out to be the mean value of the dispersion coefficients of the two types of fibers of the system, which is then called “central dispersion.” These two parameters are used to control and optimize the MI process. In particular, we establish the existence of a critical region of the central dispersion at…
Supercontinuum to solitons: New nonlinear structures in fiber propagation
2010
We review our recent work in the field of optical rogue wave physics and applications. Beginning from a brief survey of the well-known noise and incoherence processes in optical fiber supercontinuum generation, we trace the links to recent developments in studying the emergence of high contrast localised breather structures in both spontaneous and induced nonlinear instabilities. In the latter case, we discuss our recent measurements that have reported the experimental observation of the Peregrine soliton, a unique class of rational soliton predicted to exist over 25 years ago and never previously observed.
Nonlinear dynamics of a semilinear photorefractive oscillator
2001
The experimental study of the dynamics of an empty coherent semilinear photorefractive oscillator is reported. It is shown that starting from a certain coupling strength the oscillation occurs with two frequencies shifted symmetrically with respect to the frequency of the pump wave. The threshold of bifurcation in oscillation spectrum depends on pump intensity ratio.
Leading SU(3)-breaking corrections to the baryon magnetic moments in Chiral Perturbation Theory
2008
We calculate the baryon magnetic moments using covariant Chiral Perturbation Theory ($\chi$PT) within the Extended-on-mass-shell (EOMS) renormalization scheme. By fitting the two available low-energy constants (LECs), we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using Heavy Baryon (HB) $\chi$PT and covariant Infrared (IR) $\chi$PT. We also analyze the source of this improvement with particular attention on the comparison between the covariant results.
THE ρ MESON IN FINITE VOLUME
2014
We evaluate energy levels of the ππ system in the ρ channel in finite volume using chiral unitary theory. We investigate ππ phase shifts and ρ meson properties using Lattice QCD data with high precision. We also investigate the dependence on the π mass.
Study of the ππ system in a finite volume
2014
We evaluate energy levels of the ππ system in the ρ channel in a finite volume using chiral unitary theory. We investigate ππ phase shifts and ρ meson properties using Lattice QCD data with high precision. We also shortly discuss the πK system in the K* channel in a finite volume.
Vector correlator and scale determination in lattice QCD
2013
We implement a proposal made in [arXiv:1107.4388] to determine the lattice spacing by matching the lattice vector correlator at a reference distance scale with the same correlator obtained by a dispersion relation based on the $R$-ratio determined experimentally. We work with the isovector current, requiring a separation of the isovector hadronic final states on the phenomenological side. We also discuss the finite-size effect on the correlator, which must be controlled in order for the method to be applicable.
Relativistic corrections to the Drell-Hearn-Gerasimov sum rule in the constitutent quark model
1994
Relativistic corrections have been calculated for the Drell-Hearn-Gerasimov sum rule in the framework of the constituent-quark model. These corrections lead to additional absorption strength due to relativistic dipole currents in the case of a hyperfine interaction. The introduction of anomalous magnetic moments requires a subtraction of the dispersion integral at infinity. The additional effects of such anomalous moments, however, are numerically very small within the model.
Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f[sub 0](980), a[sub 0](980) scalar mesons
1998
We use a nonperturbative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f0 and a0 resonances. The ππ→ππ, ππ→KK phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π0η and KK mass distributions in the T=1 channel. Furthermore, the total and partial decay widths of the f0 and a0 resonances are properly reproduced. The results seem to indicate that chiral symmetry constraint…