A non-plasma approach to the soft dilepton production inhA andAA collisions

We propose a method of evaluating the soft dilepton production rate in hadron-nucleus and nucleus-nucleus collisions at high energies based on summing the contributions from quark-antiquark systems (chains) created in individual hadron-nucleon interactions. The individual contributions are determined by using the square dependence of the soft dilepton production rate on hadron multiplicity predicted for hadron-hadron collisions by the soft-quarkannihilation model and observed recently inpp collisions at the CERN ISR. The possibility of additional contributions originating from the annihilation of quarks and antiquarks that belong to different chains is taken into account in a phenomenological way, which nevertheless enables to correlate different phenomena in soft dilepton production. More detailed predictions are given for proton-nucleus collisions at 200 GeV/c.     

Factorization and the soft overlap contribution to heavy-to-light form factors

Using the formalism of soft-collinear effective theory, a complete separation of short- and long-distance contributions to heavy-to-light transition form factors at large recoil is performed. The universal functions ζ_M(E) parameterizing the “soft overlap” contributions to the form factors are defined in terms of matrix elements in the effective theory. Endpoint configurations corresponding to kinematic situations where one of the valence partons in the external mesons carries very small momentum are accounted for in terms of operators involving soft-collinear messenger fields. They contribute at leading order in Λ_QCD/E and spoil factorization. An analysis of operator mixing and renormalization-group evolution in the effective theory reveals that the intermediate scale is without significance to the soft functions ζ_M(E), and that the soft overlap contribution does not receive a significant perturbative (Sudakov) suppression.     

Soft gluon radiation in Higgs boson production at the LHC

We examine the contributions of soft gluons to the Higgs production cross section at the LHC in the Standard Model and its minimal supersymmetric extension. The soft gluon radiation effects of this reaction share many features with the Drell-Yan process, but arise at lowest order from a purely gluonic initial state. We provide an extension of the conventional soft gluon resummation formalism to include a new class of contributions which we argue to be universal, and resum these and the usual Sudakov effects to all orders. The effect of these new terms is striking: only if they are included, does the expansion of the resummed cross section to next-to-leading order reproduce the exact result to within a few percent for the full range of Higgs boson masses. We use our resummed cross section to derive next-to-next-to-leading order results, and their scale dependence. Moreover, we demonstrate the importance of including the novel contributions in the resummed Drell-Yan process.     

Radiative corrections to the Drell-Yan process at large dilepton invariant masses

Electroweak radiative corrections to the neutral-current Drell-Yan process at large dilepton invariant masses are calculated. Asymptotic expressions are obtained for diagrams involving two-boson exchange, which represent one of the most significant contributions to the reaction being studied. The contributions of vertex diagrams and “soft” bremsstrahlung are also taken into account. A numerical analysis of electroweak effects with allowance for experimental constraints at the CMS facility is given. The result obtained from this analysis makes it possible to ensure a high precision in the region of high energies; therefore, it is applicable to future experiments at LHC.     

On the effect of viscosity in scattering from partially coated infinite cylinders

This paper considers the two-dimensional problem of scattering of a plane wave incident on an infinite cylinder that is coated with strips of pressure-release material extending over quadrants on the illuminated and shadowed sides, with the remainder of the surface considered to be rigid. Transitions from soft to rigid surfaces correspond to discontinuous boundary conditions. Ideal fluid theory predicts an infinite pressure gradient at these transitions, which suggests that viscous effects may be significant. The present work is a quantitative analysis of the global effect on acoustic scattering of viscosity effects arising in the vicinity of the discontinuity. The analysis represents the scattered field in terms of acoustic and vortical contributions. Both contributions are represented by series expansions in terms of azimuthal harmonics and associated cylindrical wave functions. The amplitudes of these harmonics are determined by satisfying a pair of discontinuous boundary conditions. Results obtained by using the method of weighted residuals are shown to be less accurate than those obtained from a collocation procedure. The results for surface pressure and farfield directivity indicate that viscous effects are important only if the Reynolds number is extremely small.     

QED background to heavy lepton production ine + e − annihilation

The paper presents two measures, which are infrared stable and which easily relate to known properties of soft hadronic jets. The measures allow for an approximate addition of contributions from individual phases in multistep processes; the contributions from typical initial parton configurations, from evoluting jets and from final state (confinement) fluctuations are evaluated with suitable approximations in a general quantum chromodynamical framework.     

X‐ray‐Raman‐scattering‐based EXAFS beyond the dipole limit

X‐ray Raman scattering (XRS) provides a bulk‐sensitive method of measuring the extended X‐ray absorption fine structure (EXAFS) of soft X‐ray absorption edges. Accurate measurements and data analysis procedures for the determination of XRS‐EXAFS of polycrystalline diamond are described. The contributions of various angular‐momentum components beyond the dipole limit to the atomic background and the EXAFS oscillations are incorporated using self‐consistent real‐space multiple‐scattering calculations. The properly extracted XRS‐EXAFS oscillations are in good agreement with calculations and earlier soft X‐ray EXAFS results. It is shown, however, that under certain conditions multiple‐scattering contributions to XRS‐EXAFS deviate from those in standard EXAFS, leading to noticeable changes in the real‐space signal at higher momentum transfers owing to non‐dipole contributions. These results pave the way for the accurate application of XRS‐EXAFS to previously inaccessible light‐element systems.     

QED corrections to the forward backward asymmetry with extraZ bosons fore + e −→f + f −

The complete standard model corrections together with the QED contributions from an additionalZ boson to the forward backward asymmetry of the reactione ⁺ e ^?→(ψ,Z, Z′, ...)→f ⁺ f ⁺ are calculated. They include soft photon exponentiation and a cut on the photon energy. Some numerical applications are considered forE ₆ generated extraZ bosons. Though being small at TRISTAN and LEP1 energies, the QED corrections due toZ′ exchange are very important near and above theZ′ peak.     

Frequency dispersion of effective conductivity of high-temperature superconductors in the normal phase

The paper is devoted to the presently widely discussed question of the electrodynamic properties of high-temperture superconducting ceramics in the normal phase. The effective-dielectric-constant method is used to take into account the influence of the soft phonon modes connected with the structural phase transition accompanying the superconducting transition. The presence of soft phonons gives grounds for assuming that there exists a frequency region in which the contributions of the electron and phonon subsystems can be comparable. The frequency dependences of the effective conductivity and of the dielectric constant are investigated. Estimates show that an anomalous decrease of the effective conductivity should be observed, as was recently done in a number of experiments, in the microwave region. The influence of the dynamic character of the soft modes is also discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 39–42, December, 1989.     

CP Violation and Flavor Changing Effects in K and B Mesons from Nonuniversal Soft Breaking Terms

We analyze CP violation and flavor changing effects in a minimal supersymmetric standard model with arbitrary nonuniversal soft breaking. Large flavor changing neutral current effects are naturally expected in the K system, even in the absence of quark-squark flavor misalignment. However, the B system is sensitive to new supersymmetric contributions only if nonuniversality implies, not only different soft terms for the three generations but also a large quark-squark misalignment. The only exceptions are processes with a leading chirality changing contribution proportional to tanbeta (as b-->sgamma).     

Elastooptic effect and sources of the spontaneous birefringence in Gd2(MoO4)3

It is shown that a shear stress applied to support the spontaneous shear in improper ferroelectric Gd₂(MoO₄)₃(GMO) reduces the birefringence Δn'₁₂ measured when viewing along the c-axis. The elastooptic coefficient p₆₆^E in the paraelectric phase has been determined including sign. Using these and known electrooptical data, the soft mode, electrooptic and elastooptic contributions to Δn′₁₂ of GMO are evaluated. The two latter contributions have opposite sign to that of the soft mode which plays a prevailing role.     

Effect of point defects on the behavior of the soft mode at a structural phase transition

We obtain, in the model of point defects, formulas for the temperature and concentration dependences of the damping of the soft mode frequency in the vibrational dynamics regime and corrections to the relaxation frequency and to the damping constant for the overdamped regime. We consider the case of unpolarized point defects in a random field model. It is shown that temperature anomalies of a specified magnitude and the number of contributions in the lower order in anharmonism near the structural phase transition temperature depend substantially on the dynamic behavior of the soft mode. The estimates show that the contributions caused by the defects can, under certain conditions, equal or even exceed fluctuational contributions. We discuss applications of these results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 39–44, August, 1989.The author wishes to thank A. P. Levanyuk for useful discussions of the work and criticisms.     

c→uγ in the minimal supersymmetric standard model

The minimal supersymmetric standard model (MSSM) with universal soft breaking terms has a negligible effect on the rare c→uγ decay rate. We therefore study a general model with non-universal soft breaking terms constrained by vacuum stability and the experimental upper bound on the mass difference of the neutral charm mesons. It turns out that gluino exchange can enhance the standard model rate by up to two orders of magnitudes; in contrast, the contributions from charginos and neutralinos remain at least an order of magnitude below the QCD corrected standard model rate.     

A nonlinear effect observed during the modification of the structure of polyethylene irradiated by intense soft x-rays

The processes in polymers caused by high-fluence soft x-ray irradiation (on the order of tens of kW/cm²) are considered. Experimental results on the irradiation of polyethylene by soft x-ray radiation at various irradiances are presented. At a fixed fluence, the radiochemical yield of the formation of double bonds is demonstrated to increase with the irradiance. The possible mechanisms of this phenomenon are discussed.     

Dipolar interaction in the transverse Ising model of H-bonded ferroelectrics

Numerical solutions are presented for the set of approximated kinetic equations previously obtained to describe the dynamical behaviour of the pseudospin correlation functions of the transverse Ising model in H-bonded ferroelectrics. Stability of the soft mode and spectral characteristics of the correlation functions as T → ∞ are discussed in terms of an interaction made of both nearest-neighbour and dipole-dipole contributions. This infinite-temperature calculation shows how shift (towards zero frequency) and width of the soft mode vary with the interdipolar strength of the interaction. The asymmetry of the imaginary part of susceptibility _X″zz(ω) exhibited by KDP in its paraelectric phase is also shown to be due to the dipolar character of the interaction.     

Trends in the electronic and vibrational contributions to the dipole moment,polarizabilities, and first and second hyperpolarizabilities of the hydrides of Li,Na and K

The dipole moments μ, polarizabilities α, and first and second hyperpolarizabilities, β and γ of LiH, NaH and KH (MeH) have been computed using Hartree-Fock, MP2 and CCSD(T) theories. The static electronic and vibrational contributions to these properties are presented. The vibrational properties have been analysed into contributions due to zero-point vibrational averaging and pure vibrational terms. An alternative dissection of the vibrational properties into nuclear relaxation and curvature terms has also been considered. KH has been selected as a model system to study how the number of electrons, which are correlated (2, 10 and 20) affect both electronic and vibrational properties. The 10 electron approximation gives results that are practically the same as those computed by taking into account all 20 electrons of KH. The double-harmonic approximation has been shown to give satisfactory results for the pure vibrational contributions to the polarizability and the first hyperpolarizability, while this approximation is useful for demonstrating, qualitatively, the significance of the pure vibrational contributions to the second hyperpolarizability. In many cases the vibrational contributions are rather small percentages of the corresponding electronic contribution. However, several exceptions to the above observation have been noted. In all the cases considered the vibrational properties should be computed if reasonably accurate property values are sought. Electron correlation is important for both electronic and vibrational contributions to the electrical properties of the hydrides considered. The results are in satisfactory agreement with most of the best theoretical and experimental data concerning bond lengths, vibrational frequencies and electrical properties.     

Low momentum penguin loop contributions and the ΔI=1/2 rule

Contributions to the penguin diagram due to low loop momenta are considered. Using a chiral effective field theory including quarks coupling to pions and kaons, sizeable contributions fromu-quark loop momenta below the chiral symmetry breaking scale are found. Thus a previous result obtained within the bag model is confirmed. It is concluded that the low momentum penguin loop contributions seem to improve the theoretical understanding of the ΔI=1/2 rule.