On the origin of scaling violations in fragmentation functions

We show that the scaling violations observed in the fragmentation functions of neutrino scattering can be mostly of a kinematical origin and not necessarily from a QCDQ ²-evolution. Due to confinement effects, the application of such evolution equations is nontrivial at non-asymptotic energies, but these QCD effects can be taken into account by a dynamical simulation of the parton branching processes followed by a string fragmentation method.     

Strong coupling constant from the photon structure function

We extract the value of the strong coupling constant alpha(s) from a single-parameter pointlike fit to the photon structure function F(gamma)(2) at large x and Q(2) and from a first five-parameter full (pointlike and hadronic) fit to the complete F(gamma)(2)data set taken at PETRA, TRISTAN, and LEP. In next-to-leading order and the MS renormalization and factorization schemes, we obtain alpha(s)(m(Z))=0.1183+/-0.0050(expt)(+0.0029)(-0.0028)(theor) (pointlike) and alpha(s)(m(Z))=0.1198+/-0.0028(expt)(+0.0034)(-0.0046)(theor) (pointlike and hadronic). We demonstrate that the data taken at LEP have reduced the experimental error by about a factor of 2, so that a competitive determination of alpha(s) from F(gamma)(2) is now possible.     

Energy conservation and scaling violations in particle production

We use a simple Colour Glass Condensate/String Percolation Model argument to show the existence, due to energy conservation, of bounds to the violation of Feynman scaling and limiting fragmentation.     

Gluon fragmentation functions from quark jets

The analysis of events with a fixed, different from unity, fraction of energy flowing into a solid angle ΔΩ can be used to extract the probability functions related to the scaling violations of deep inelastic scattering. One can obtain from the study of a quark jet, both the gluon and the quark fragmentation functions into hadrons.     

Testing QCD scaling violations in the HERA energy range

High energy electron-proton colliders open new kinematical domains for the investigation of scaling violations in nucleon structure functions. Focussing on HERA as a definite study case we explore the precision which can be expected in determinations of the QCD scale parameter Λ and the running coupling constant α _s (Q ²). Our results provide a quantitative basis for discussions of the possibilities and requirements of QCD tests in inclusive deep inelastic scattering at HERA energies.     

Calculation of the green functions by the coupling constant dispersion relations

The discontinuities of the Green functions on the cut in the complex plane of the coupling constant are calculated by the steepest descent method. The saddle points are given by the solutions of the classical field equations at those values of the coupling constant for which the classical theory has no ground state. The Green functions at the physical values of the coupling constant are determined by dispersion relations.     

Subleading long-range interactions and violations of finite size scaling

We study the behavior of systems in which the interaction contains a long-range component that does not dominate the critical behavior. Such a component is exemplified by the van der Waals force between molecules in a simple liquid-vapor system. In the context of the mean spherical model with periodic boundary conditions we are able to identify, for temperatures close above T _c, finite-size contributions due to the subleading term in the interaction that are dominant in this region decaying algebraically as a function of L. This mechanism goes beyond the standard formulation of the finite-size scaling but is to be expected in real physical systems. We also discuss other ways in which critical point behavior is modified that are of relevance for analysis of Monte Carlo simulations of such systems. Received 21 November 2000 and Received in final form 28 February 2001     

Strong coupling from inclusive semileptonic decay of charmed mesons

In this study,we employed the heavy quark expansion model with the kinetic scheme to evaluate α_S（m_c²）,the strong coupling constant at the charm quark mass m_c, using data on inclusive semileptonic decays of charmed mesons.Using the experimental values of the semileptonic decay widths of the D⁰ and the D⁺,the value of α_s（m_c²）was determined to be 0.445±0.009±0.114,where the first uncertainty is experimental and the second is systematic.This value of α_s（m_c²） is in good agreement with the value of α_s（m_c²） which calculated by running α_S（m_Z²） at the Z⁰ boson mass m_Z with the renormalization group evolution equation.In addition,the values of α_s（m_c²） obtained individually from each of the D⁰,D⁺,and D_s⁺ mesons were consistent,as they were of the same origin.     

Strong dynamic magnetoelectric coupling in metamaterial

Magnetoelectric susceptibility (ξ) of classical magnetoelectrics is always substantially smaller that the geometric average of the electric (χ _e ) and magnetic (χ _m ) susceptibilities. Materials reaching the equality ξ ² = χ _e χ _m as a limiting value may thus be considered as ideal magnetoelectrics. Here we investigate the magnetoelectric susceptibility of a metamaterial built from split ring resonators both experimentally and within an equivalent circuit model. Due to a direct proportionality between electric polarization and magnetization, the magnetoelectric susceptibility of this metamaterial fulfils the equality ξ ² = χ _e χ _m at least in the dynamic regime.     

Strong coupling regime in semiconductor microcavities

We introduce to the physics of semiconductor microcavities in the strong coupling regime, also known as cavity-polariton. We discuss the optical response, cavity-polariton dispersion curve, inhomogeneous broadening due to disorder effect and homogeneous broadening due to acoustic phonon scattering. We present novel effects on high quality samples on elastic scattering and parametric oscillation effects in the non-linear response under resonant excitation. To cite this article: R. Houdré et al., C. R. Physique 3 (2002) 15–27     

Strong coupling in a microcavity LED

Thin films of polyelectrolyte/J aggregate dye bilayers with high absorption coefficient (6 nm thick with alpha approximately equal to 1.0 x 10(6) cm(-1)) inserted in an optical microcavity enable the cavity quantum electrodynamic strong coupling limit to be reached at room temperature with a coupling strength (Rabi splitting) of 265 +/- 15 meV. By embedding these films in a resonant cavity organic LED structure, we demonstrate the first emissive electrically pumped exciton-polariton device.     

Perturbative vs. non-perturbative scaling violation in quark fragmentation

We investigate the approach to scaling for non-perturbative quark fragmentation in the frame-work of the uncorrelated jet model. It is found that subasymptotic kinematic scale breaking is comparable in size to scaling violations from hard gluon emission a la QCD. Experimental data available at present do allow for such non-perturbative scale breaking effects.