The nonlinear effects of quantum electrodynamics at high energies

In this paper we considere ⁺ e ^? scattering with intermediate photon-photon scattering as a possibility for getting information about the nonlinear effects of quantum electrodynamics (QED) at high energies. This process is a higher-order correction to double bremsstrahlung. However, these two processes have quite different behaviour with the photon-photon scattering angle. Here we calculate the unpolarized differential cross section of thee ⁺ e ^? scattering with intermediate γγ scattering and also the interference terms with the double bremsstrahlung. Moreover, we show that the sum of these two contributions predominates over the contribution of the double bremsstrahlung for sufficiently large scattering angles of the photons. This result enables us to extract the differential cross section of the γγ scattering. Through extrapolation to different kinematical conditions we can get the cross sections for nearly real photon-photon scattering, photon splitting and Delbrück scattering. As a quantitative example we use the result for a test of the electron propagator in a gauge-invariant way with the usual minimal interaction. We give also numerical examples of this test, which will improve the present values of the testing parameters.     

Hadron production from photon-photon interactions in the CM energy range from 1 to 5 GeV

We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e⁺e^? storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.     

The calculation of twist-4 corrections to the photon structure function

The twist-4 corrections to the photon structure function are calculated by the method previously suggested by the authors [1], using the operator expansion in the photon virtualityp ² and correct analytical properties of photon-photon scattering amplitude inp ².Work supported in part by Schweizerischer Nationalfonds     

Calculation of Elastic Scattering Properties in an Ultra-Cold ^85Rb-^85Rb Vapour

We report the calculation of the same-species elastic scattering properties for the ultracold rubidium-rubidium (^85Rb-^85Rb) system and the results are compared with other theoretical and experimental results in detail. We present an improved potential for triplet ground states of the Rb2 molecule, and calculate the scattering lengths αt and the effective range re using WKB and Numerov methods for two rubidium-85 collisions in the triplet state. Also, we investigate the convergence of these scattering properties, i.e. the dependence on core radius and K^0 parameter using quantum defect theory and the analytic calculations of scattering length obtained by Szmytkowski. In addition, we present evaporative cooling and other results that include phase shift and cross section at zero energy limit.     

Ultraviolet and soft X-ray photon-photon elastic scattering in an electron gas

We have considered the processes which lead to elastic scattering between two far ultraviolet or X-ray photons while they propagate inside a solid, modeled as a simple electron gas. The new ingredient, with respect to the standard theory of photon-photon scattering in vacuum, is the presence of low-energy, nonrelativistic electron-hole excitations. Owing to the existence of two-photon vertices, the scattering processes in the metal are predominantly of second order, as opposed to fourth order for the vacuum case. The main processes in second order are dominated by exchange of virtual plasmons between the two photons. For two photons of similar energy , this gives rise to a cross section rising like ² up to maximum of around 10^–32 cm², and then decreasing like ^–6. The maximal cross section is found for the photon wavevectorkk _F , the Fermi surface size, which typically means a photon energy in the keV range. Possible experiments aimed at checking the existence of these rare but seemingly measurable elastic photon-photon scattering processes are discussed, using in particular intense synchrotron sources.     

自发破缺规范理论中的光子-光子散射

本文在SU(2)_L×U(1)模型里研究中间态的W介子对光子-光子散射的贡献。由于自发破缺规范理论的可重整化性以及自发破缺以后电磁规范不变性仍成立,在单迴路近似下,光子-光子散射幅中的无穷大必然互相抵消。本文用具体计算说明这一点,并且在低能近似下给出电磁场的等效非线性相互作用拉格朗日量和散射截面。在低能近似下,轻子中间态对散射的贡献为主,然而在高能极限下,W介子中间态的贡献将变得可以和轻子中间态的贡献相比较。     

Photon-photon scattering in effective-photon theory

Effective photon theory of laser-induced gas breakdown is shown to imply a very large photon-photon scattering cross section in the vacuum, of the order of 10^-22cm². This could be seen using crossed laser beams of moderate intensity, about 1 MW/cm².     

Using high-power lasers for detection of elastic photon-photon scattering

The properties of four-wave interaction via the nonlinear quantum vacuum is investigated. The effect of the quantum vacuum is to generate photons with new frequencies and wave vectors, due to elastic photon-photon scattering. An expression for the number of generated photons is derived, and using state-of-the-art laser data it is found that the number of photons can reach detectable levels. In particular, the prospect of using the high-repetition Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The problem of noise sources is reviewed, and it is found that the noise level can be reduced well below the signal level. Thus, detection of elastic photon-photon scattering may for the first time be achieved.     

Global analysis of the strangeness vector and axial form factors of the nucleon and their uncertainties

We have studied the strangeness contribution to the elastic vector and axial form factors of the nucleon, using all available electroweak elastic scattering data sensitive to these contributions. Specifically, we combine ??p and $\bar{\nu} p$ elastic scattering cross sections from Brookhaven E734 with parity-violating asymmetries in elastic ep scattering, and quasi-elastic ed and e ⁴He scattering, observed in the SAMPLE, HAPPEx, G0 and PVA4 experiments. We are able not only to determine these form factors at individual values of momentum-transfer (Q ²), as has been done recently, but also to fit the Q ²-dependence of these form factors using simple functional forms. We present the results of these fits using existing data.     

Unitarity, (anti)shadowing, and black-disk limit

By using realistic models for elastic hadron scattering, we demonstrate that, at current accelerator energies, the s-channel unitarity bound is safe and is not to be reached until 10⁵ GeV, while the black-disk limit is saturated around 6 TeV. It will be followed by a larger transparency of the scattered particles near the center.     

Inelastic electron photon scattering at moderate four-momentum transfers

We present new high statistics data on hadron production in photon-photon reactions. The data are analyzed in terms of an electron-photon scattering formalism. The dependence of the total cross section of Q², the four-momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector-Meson Dominance and the quark model.     

Two-photon collisions in deep inelastic lepton-nucleon and lepton-nucleus scattering

We have calculated the μ-pair production via photon-photon collisions in deep-inelastic charged lepton scattering on proton and nuclei, using the equivalent photon approximation. Specific parametrizations were assumed for the proton and the nuclei form factors and the QED photon structure function. Results are given for lepton energies below 300 GeV and virtual photon massesQ ² less than 50 GeV², as functions of the μ-pair mass, the scaling variablex and the electric chargeZ of the hadron target. Using a photon structure function derived from QPM and VDM we also estimate the contribution of γγ collisions to hadron production in these deep inelastic processes.     

Elastic and inelastic scattering of 18O by 16O and 18O

Angular distributions have been measured for the elastic and inelastic scattering of ¹⁸O by ¹⁶O and ¹⁸O at laboratory bombarding energies of 42 and 52 MeV. The inelastic scattering data are analyzed in terms of collective excitations using a coupled channel approach. Deformation parameters are obtained for the strongly excited states. The relationship between the strength of inelastic scattering and the amount of structure in the elastic scattering distributions is discussed.     

Resonances inη-light nucleus systems

We locate resonances inη-light nucleus elastic scattering using the time delay method. We solve few-body equations within the finite rank approximation in order to calculate the t-matrices and hence the time delay for theη-³He andη-⁴He systems. We find a resonance very close to the threshold inη-³He elastic scattering, at about 0.5 MeV above threshold with a width of ∼2 MeV. The calculations also hint at the presence of sub-threshold states in both the cases     

Eikonal description of quantal scattering

Elastic and inelastic quantal scattering is described by a theory in which the contribution of a range of impact parameters to the scattering amplitude is determined by a phase integral (“eikonal”) which is integrated along a real curved “quantal” trajectory. This amplitude reduces to the Glauber expression in the high-energy, forward-angle limit, and to the usual semiclassical amplitude in the classical limit. The formulation can be applied to the study of heavy-ion scattering. The quantal trajectories are investigated analytically for the case of Coulomb scattering. A numerical analysis of elastic ¹⁶O¹⁶O scattering is carried out. The results show appreciable improvement as compared with the Glauber approximation.     

Propagation of gamma-rays at cosmological redshifts

We discuss absorption and reprocessing of γ-rays at cosmological redshifts. We consider Compton scattering and pair production by γ-rays on the cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by γ-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. We point out the cosmological importance of photon-photon scattering (a process not previously considered in astrophysics). We determine the region where the universe is transparent to γ-rays and the regions of dominance of the elementary processes on the photon-energy-redshift plane. We discuss the current status of this field of research and its future directions. The problem of cosmological γ-ray reprocessing is relevant, e.g., for observational γ-ray astronomy, for which the signatures of the cosmological origin need to be determined, and for studies of the effects that pair cascades, caused by the decay of unstable particles from a hot Big Bang, have on the primordial nucleosynthesis.     

Optical model analysis of p+6He scattering over a wide range of energy

Optical-model analysis of proton elastic scattering from ⁶He has been carried out for eight sets of elastic scattering data at energies, 24.5, 25.0, 36.2, 38.3, 40.9, 41.6, 71.0 and 82.3 MeV/n respectively. The vector analyzing power and differential cross section for the elastic scattering of ⁶He nucleus from polarized protons at 71 MeV have been analyzed in the framework of the optical model potentials. The data are, first, analyzed in term of phenomenological potentials using the Woods-Saxon form for the real and imaginary parts supplemented by a spin-orbit potential of Thomas form. The analysis has been also performed using microscopic complex potentials.     

Application of the diffraction theory to proton scattering by the 15C nucleus in inverse kinematics

The calculation of the amplitude of proton elastic scattering by unstable neutron-rich nucleus ¹⁵C within the Glauber diffraction theory with the ¹⁵C nucleus wave function in the multiparticle shell model is presented. In optical limit approximation (single scattering), the differential cross section of proton elastic scattering is calculated at energies of 0.2, 0.6, and 1 GeV/nucleon. For an energy of 0.2 GeV/nucleon, the contribution of double scattering, determining the differential cross section at angles exceeding 20° is taken into account. Original Russian Text ? E.T. Ibraeva, A.M. Zhusupov, O. Imambekov, G. Nurbakova, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 892–897.     

Theoretical LSP detection rates for <Superscript>71</Superscript>Ga, <Superscript>73</Superscript>Ge,and <Superscript>127</Superscript>I dark-matter detectors

The low-energy structure of the dark-matter detector nuclei ⁷¹Ga, ⁷³Ge, and ¹²⁷I has been studied by using the microscopic quasiparticle-phonon model. The resulting ground states have been used to calculate theoretical predictions for detection rates of the lightest supersymmetric particle (LSP) in experiments studying elastic scattering of an LSP from an atomic nucleus. The highest rate, approximately 0.27 yr^?1kg^?1, among all the adopted SUSY parameters and renormalization schemes was provided by ¹²⁷I at the zero limit of the detector energy threshold.     

On the light-by-light contribution to the sixth-order muon anomaly

We have evaluated analytically the coefficient of log m_μ/m_e for the six photon-photon scattering diagrams contributing to the muon g ? 2 in sixth order. The result is remarkably simple, 2π²/3, in complete agreement with the latest numerical evaluation. This completes the analytic calculation of all logarithmic terms in sixth order.