Standard radiation spectrum of relativistic electrons: beyond the synchrotron approximation

Radiation emitted by an electron in arbitrary, extreme relativistic motion, has been described for the first time in terms of a standard spectrum of nonsynchrotron type. Ultimately, such a nonsynchrotron spectrum is dependent not only on instantaneous trajectory curvature, but also upon its first two time derivatives and helicity, to provide a basic correction to the synchrotron approximation (SA). A strong deviation from SA has been predicted for above GeV electrons in oriented crystals.     

Entangled and disentangled decoherence of intermediate electron-hole pairs in two-photon photoemission from surface bands: beyond the adiabatic approximation

We discuss the effects which combinations of entangled and disentangled decoherence and transient response induce on the early decay of coherent electron-hole pairs in the intermediate states of two-photon photoemission (2PPE) from image potential bands. We find that their interplay gives rise to deviations of the pair decay probabilities from simple exponential laws governed by independent quasiparticle lifetimes obtained in the self-energes based on the adiabatic hypothesis. Assessment of these effects for paradigmatic Cu(111) surface shows that they are most pronounced in the interval of pump-probe photon pulse delay times typical of current 2PPE experiments.     

Quark charges and colour gluon mass from deep-inelastic bremsstrahlung

We derive sum rules for the structure functionV(x) for the ‘three-photon’ processe ^±+p→e ^±+γ+X which can distinguish between various colour models below colour threshold, independently of the quark and gluon distributions. A careful study of the sum rule forV(x) in the broken colour gauge theory model can in principle be used to determine the colour gluon mass. Invoking the specific assumptions of the dominance ofp-type quarks and neglecting the sea of quark-antiquark pairs, we also obtain bounds forV(x) in terms ofvW ₂ (x) which can distinguish between various colour models below colour threshold.     

The gluon distributions in the smallx region beyond the leading order

The gluon distributions in a proton are calculated in the region of smallx (10^?4?x?10^?2) and largeQ ² taking into account the corrections which correspond to the sum of the leading powers of log 1/x beyond the leading logQ ² approximation. It is shown that they become significant for very small values ofx only provided however that the non-leading terms in the limit of smallx are also consistently included. The leading log 1/x approximation gives the gluon distributions which can differ by a factor of 2 from their leading logQ ² counterpart.     

Chiral condensate beyond the one-loop approximation

A two-dimensional model involving a fermion field and a self-interacting scalar field with Yukawa interaction is studied beyond the one-loop approximation. It is shown that, in this model, the chiral condensate vanishes at two values of the Yukawa coupling constant. In one case, the respective symmetry is restored, while, in the other case, it is not restored.     

Airy beams beyond the paraxial approximation

The behavior of the vectorial Airy beams beyond the paraxial approximation is investigated. Indeed, closed-form (even though non exact) expressions for the electric components of the fields generated by the same boundary conditions, which should pertain to the scalar Airy beams, are obtained on the basis of the vectorial Rayleigh-Sommerfeld diffraction integrals under suitable approximations. Such expressions may accompany more complete approaches, like that in Opt. Expr. 17, 22432 (2009), where a fully numerical analysis of the propagation of exponentially smoothed Airy beams has been presented, faithfully reproducing the conditions of their experimental demonstration as reported in Phys. Rev. Lett. 99, 213907 (2007). Comments on other well known approaches to the investigation of the nonparaxial propagation of definite paraxial beams are also given.     

Effective gluon interactions in the colour superconductive phase of two flavor QCD

The gluon self-energies and dispersion laws in the color superconducting phase of QCD with two massless flavors are calculated using the effective theory near the Fermi surface. These quantities are calculated at zero temperature for all the eight gluons, those of the remaining SU(2) color group and those corresponding to the broken generators. The construction of the effective interaction is completed with the one loop calculation of the three- and four-point gluon interactions.     

Measurement of QCD parameters by using the single dressed gluon approximation

This article is based on renormalization analysis by using the single dressed gluon (SDG) approximation. This model is used to measure the coupling constant in perturbative as well as in the nonperturbative part of the QCD theory. We employ the event shape observables 〈B _T〉, 〈B _W〉, 〈1 ? T〉, 〈C〉, and 〈ρ〉. By fitting both Monte Carlo and the real data with SDG, we find the mean values \({\alpha _S}\left( {{M_{{Z^0}}}} \right)\) = (0.1215 ± 0.0030) GeV and ν = (1.2685 ± 0.0173) GeV in the perturbative and nonperturbative regions, respectively. Our results are consistent with those obtained from other experiments at different energies. We explain all these features in this paper.     

Vectorial Hermite--Laguerre--Gaussian beams beyond the paraxial approximation

Starting from the vectorial Rayleigh--Sommerfeld integrals, the free-space propagation expressions for vectorial Hermite--Laguerre--Gaussian (HLG) beams beyond the paraxial approximation are derived. The far-field expressions and the scalar paraxial results are given as special cases of our general expressions. The intensity distributions of vectorial nonparaxial HLG beams are studied and illustrated with numerical examples.     

Time-dependent density-functional theory beyond the local-density approximation

Approximations for the ground-state exchange-correlation potential of density-functional theory have reached a high level of sophistication. By contrast, time- or frequency-dependent exchange-correlation potentials are still being treated in a local approximation. Here we propose a novel approximation scheme, which effectively brings the power of the generalized gradient approximation (GGA) and meta-GGA to time-dependent density-functional theory. The theory should allow a more accurate treatment of strongly inhomogeneous electronic systems (e.g. molecular junctions) while remaining essentially exact for slowly varying densities and slowly varying external potentials.     

Saturation of gluon density and soft pp collisions at LHC

We find the relation of the unintegrated gluon distribution at low intrinsic transverse momenta to the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. It allows us to study the saturation of the gluon density at low Q ² more carefully and find the saturation scale that does not contradict to both the LHC and HERA data.     

The QCD generalized parton model and a next-to-leading approximation of the gluon density

Using recent neutrino data, we calculate in the framework of the generalized parton model the modification of the gluon density caused by next-to-leading logarithmic effects. We find that they are of the same order of magnitude as the experimental uncertainties, and that the gluon density tends to be more peaked towards small x.     

Nonperturbative gluon radiation and energy dependence of elastic scattering

The energy dependence of the total hadronic cross sections is caused by gluon bremsstrahlung which we treat nonperturbatively. It is located at small transverse distances about 0.3 fm from the valence quarks. The cross section of gluon radiation is predicted to exponentiate and rise with energy as s(delta) with delta = 0.17+/-0. 01. The total cross section also includes a large energy independent Born term which corresponds to no gluon radiation. The calculated total cross section and the slope of elastic scattering are in good agreement with the data.     

The nucleon-nucleon potential beyond the static approximation

We point out that, due to the use of static nucleon propagators in Heavy-Baryon Chiral Perturbation Theory (HBχPT), the current calculations of the nucleon-nucleon potential miss certain contributions starting at two loops. These contributions give rise to contact interactions, which are both parametrically and numerically more important than the so-called NNLO potentials. They show a peculiar dependence on the light-quark masses, which should be taken into account when performing chiral extrapolations of lattice data. However, they do not appear to have an impact on phenomenology since they can be absorbed into redefinitions of unknown parameters which are usually fitted to data.     

Lateral Casimir force beyond the proximity-force approximation

We argue that the appropriate variable to study a nontrivial geometry dependence of the Casimir force is the lateral component of the Casimir force, which we evaluate between two corrugated metallic plates outside the validity of the proximity-force approximation. The metallic plates are described by the plasma model, with arbitrary values for the plasma wavelength, the plate separation, and the corrugation period, the corrugation amplitude remaining the smallest length scale. Our analysis shows that in realistic experimental situations the proximity-force approximation overestimates the force by up to 30%.     

Transverse-electric and transverse-magnetic beam modes beyond the paraxial approximation

Transverse-electric and transverse-magnetic beam modes are considered based on a theory in which complex dipole sources and sinks are oriented along the beam axis; the theory is similar to one that was previously presented for transverse dipoles. The field in the region of the waist is explored. Modes with such polarization have been reported from a wide range of laser types.