Three-Reggeon cuts in QCD amplitudes

One of remarkable properties of QCD is the gluon Reggeization. The Reggeized gluon is the primary Reggeon in QCD; Pomeron and Odderon appear as compound states of the Reggeized gluons. Due to negative signature the Reggeized gluon gives the main contributions to high energy QCD amplitudes in each order ofperturbation theory. In the leading and next-to-leading logarithmic approximations these amplitudes aregiven by the Regge pole contributions. In the next-to-next-to-leading approximation the pole form of the amplitudes is violated by contributions of three-Reggeon cuts. We discuss these contributions to elastic QCD amplitudes.

ELASTIC SCATTERING AND THE PROTON FORM FACTOR

We use the QCD pomeron model proposed by Landshoff and Nachtmann to compute the differential and the total cross-sections for pp scattering in order to discuss a QCD-based approach to the proton form factor. This model is quite dependent on the experimental electromagnetic form factor, and it is not totally clear why this form factor gives good results even at moderate transferred momentum. We exchange the electromagnetic form factor by the asymptotic QCD proton form factor determined by Brodsky and Lepage (BL) plus a prescription for its low energy behavior dictated by the existence of a dynamically generated gluon mass. We fit the data with this QCD inspired form factor and a value for the dynamical gluon mass consistent with the ones determined in the literature. Our results also provide a determination of the proton wave function at the origin, which appears in the BL form factor.

HIGH ENERGY PHOTON–PHOTON COLLISIONS AT A LINEAR COLLIDER

High intensity back-scattered laser beams will allow the efficient conversion of a substantial fraction of the incident lepton energy into high energy photons, thus significantly extending the physics capabilities of an e-e± linear collider. The annihilation of two photons produces C = + final states in virtually all angular momentum states. An important physics measurement is the measurement of the Higgs coupling to two photons. The annihilation of polarized photons into the Higgs boson determines its fundamental H0γγ coupling as well as determining its parity. Other novel two-photon processes include the two-photon production of charged pairs τ+τ-, W+W-, [Formula: see text], and supersymmetric squark and slepton pairs. The one-loop box diagram leads to the production of pairs of neutral particles such as γγ → Z0Z0, γZ0, and γγ. At the next order one can study Higgstrahlung processes, such as γγ → W+W-W-H. Since each photon can be resolved into a W+W- pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying possibly anomalous WW collisions and annihilation. In the case of QCD, each photon can materialize as a quark anti-quark pair which interact via multiple gluon exchange. The diffractive channels in photon-photon collisions allow a novel look at the QCD pomeron and odderon. The C = - odderon exchange contribution can be identified by looking at the heavy quark asymmetry. In the case of eγ → e′ collisions, one can measure the photon structure functions and its various components. Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes which are also important for the analysis of exclusive semi-leptonic and two-body hadronic B-decays.