Total \gamma^{\star}\gamma^{\star} cross section and the QCD dipole picture

In the framework of the dipole picture of the BFKL pomeron we discuss two possibilities of calculating the total cross section of the virtual photons. It is shown that the dipole model reproduces the results obtained earlier from -factorization up to the selection of the scale determining the length of the QCD cascade. The choice of scale turns out to be important for the numerical outcome of the calculations. Received: 12 June 1997 / Published online: 20 February 1998     

The system of four reggeized gluons and the three-pomeron vertex in the high colour limit

The amplitude for 4 interacting reggeized gluons is studied in the high-colour limit. The leading order amplitude is explicitly shown to reduce to a pair of reggeons, i.e to a single BFKL pomeron. The next-to-leading order diffractive amplitude is found to split into a double pomeron exchange and triple pomeron contribution. The obtained three-pomeron vertex is different from the originally proposed in [2]. Received: 26 June 1997 / Revised version: 28 February 1998 / Published online: 3 September 1998     

On the inclusive gluon jet production from the triple pomeron vertex in the perturbative QCD

Single and double inclusive cross-sections for gluon jet production from within the triple pomeron vertex are studied in the reggeized gluon technique in the QCD with N_c→∞. It is shown that to satisfy the AGK rules the vertex has to be fully symmetric in all four reggeized gluons which form the two final pomerons. The single inclusive cross-sections are found for different cuttings of the triple pomeron vertex. They sum to the expression obtained by Kovchegov and Tuchin in the color dipole picture. The found double inclusive cross-sections satisfy the AGK rules.     

The process $\gamma(^*) + p \to \eta_c + X$: a test for the perturbative QCD odderon

The rates of inclusive photo- and electroproduction of the meson: are calculated in the triple Regge region, integrated over the diffractive mass X. For the Regge exchanges we use the hard pomeron and odderon, both being calculated in the framework of perturbative QCD. The integrated cross section depends upon the coupling of the BFKL pomeron to two C = -1 odderons, and it is found to be of the order of 60 pb for photoproduction and 1.5 pb at Q² = 25 GeV².Received: 16 April 2003, Published online: 25 February 2004     

\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998     

\gamma^* \gamma^* reactions at high energies

The total hadronic cross sections at high energy are calculated as a function of energy and photon virtuality in a model combining Reggeon exchange, the quark box diagram (a fixed pole in Regge language) and soft and hard pomeron exchanges evaluated in the context of dipole-dipole scattering. Good agreement is obtained with the data for the real cross section and for the real photon structure function . However the model prediction for the cross section is too small. This is attributed to an incorrect extrapolation of the dependence of the hard pomeron adopted here. Parametrising it independently shows that the hard part of the cross section can be well represented by a simple Regge pole with intercept . Received: 19 August 1999 / Published online: 3 February 2000     

Pomeron and odderon in high energypp andp\bar p elastic scattering

High energypp and data on elastic scattering and total cross sections are analyzed in a model including the pomeron, odderon and secondary reggeons. A dipole model is used for the pomeron and for the odderon. By construction, our (bare) pomeron ansatz produces a single dip, as observed experimentally. The model reproduces the logarithmically rising cross sections with a unit pomeron intercept, but better fits are obained when a small non-zero value of the parameter = _p (0) is allowed for. Predictions for the future accelerators (UNK, LHC, SSC) are given.On leave of absence from the Institute for Theoretical Physics, Kiev-130, USSR     

Structure function of the nucleus in the perturbative QCD with N_c\rightarrow\infty (BFKL pomeron fan diagrams)

The equation for the sum of BFKL pomeron fan diagrams is rederived by a direct summation and solved numerically for rapidities . At high rapidities, , the resulting cross-sections for the scattering of a longitudinally polarized pair on the nucleus cease to depend on its transverse dimension and tend to a constant limit of , which corresponds to scattering of a color dipole on a black disk. Thus the unitarity is restored and the singularity in the j plane is reduced to a simple pole at . The nuclear structure function at small x behaves as . The gluon density found has a soliton-like form in the log k space: its form is close to Gaussian, independent of rapidity, the center moving towards higher log k with a nearly constant velocity as the rapidity increases. Received: 26 January 2000 / Published online: 8 June 2000     

Study of Kaon-Proton Elastic Scattering at High Energies

It ia shown that the differential cross section for both K⁺p and K^-p elastic scattering including the most recent measurements for 20 < pL < 200 (GeV/c) and with -t extended upto 28 (GeV/c)² can be fitted by using the pomeron as dipole and p as a simple pole. The difference of the total cross section for K⁺p and K^-p scattering is also explained.     

BFKL pomeron propagator in the external field of the nucleus

It is shown by numerical calculations that the convoluted QCD pomeron propagator in the external field created by a solution of the Balitsky-Kovchegov equation in the nuclear matter vanishes at high rapidities. This may open a possibility to apply the perturbative approach for the calculation of pomeron loops.     

Diffractive dijet cross sections in photoproduction at HERA

Differential dijet cross sections have been measured with the ZEUS detector for photoproduction events in which the hadronic final state containing the jets is separated with respect to the outgoing proton direction by a large rapidity gap. The cross section has been measured as a function of the fraction of the photon () and pomeron () momentum participating in the production of the dijet system. The observed dependence shows evidence for the presence of a resolved- as well as a direct-photon component. The measured cross section increases as increases indicating that there is a sizeable contribution to dijet production from those events in which a large fraction of the pomeron momentum participates in the hard scattering. These cross sections and the ZEUS measurements of the diffractive structure function can be described by calculations based on parton densities in the pomeron which evolve according to the QCD evolution equations and include a substantial hard momentum component of gluons in the pomeron. Received: 20 April 1998 / Published online: 2 July 1998     

Nuclear exclusive vector meson photoproduction

We calculate the nuclear cross section for vector meson exclusive photoproduction within the QCD color dipole picture and in the Regge approach. For the former approach, we have considered the phenomenological saturation model, whereas for the latter we use a model based on the dipole pomeron framework. Theoretical estimates for scattering on both light and heavy nuclei are given over a large range of energy.Received: 17 April 2004, Revised: 21 September 2004, Published online: 18 November 2004     

Coulomb interference in high-energy pp and $\bar p p$ scattering

An analysis of the Coulombic amplitude and its interference with the nuclear amplitude which is driven by the three-component pomeron is presented. It is shown that different approaches towards the evaluation of the Coulomb phase give approximately uniform results at all energies and the differences are negligible at RHIC and LHC energies. We show that the use of the amplitude which was fitted to accommodate the nucleon data only (in the region (GeV²)), combined with the Coulomb amplitude, reproduces the existing data in the Coulomb interference domain quite accurately without any adjustment of the parameters. As a consequence, we predict the differential cross section in the region of the Coulomb nucleon interference for both RHIC and LHC energies. Received: 3 June 2002 / Revised version: 27 February 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: petrov@mx.ihep.su RID="b" ID="b" e-mail: predazzi@to.infn.it RID="c" ID="c" e-mail: prokudin@to.infn.it     

Survival probability for diffractive Higgs production in high density QCD

In this paper, the contribution of hard processes described by BFKL pomeron exchange is taken into account by calculating the first enhanced diagram. The survival probability is estimated, using the ratio of the first enhanced diagram and the single pomeron amplitude, taking into account all essential pomeron loop diagrams in the toy model of Mueller. The triple pomeron vertex is calculated explicitly in the momentum representation. This calculation is used for estimating the survival probability, and it turns out that the survival probability is small, at 0.4%. Hard pomeron rescattering processes contribute substantially to the survival probability.     

The triple pomeron interaction in the perturbative QCD

The triple pomeron interaction is studied in the perturbative approach of BFKL-Bartels. At finite momentum transfers √?t the contribution factorizes in the standard manner with a triple-pomeron vertex proportional to 1/√?t, Att=0 the contribution is finite, although it grows faster with energy than for finitet and does not factorize.     

THE DIPOLE POMERON AND K+P ELASTIC SCATTFRING UP TO 310 GeV/c

Using a dipole pomeron ansatz a good fit to the K⁺P total and near-forward elastic differential cross-sections and Re/Im data in the 35≤p2ab≤310 Gev/c region is obtained for |t|≤1(Gev/c)².     

Hadron–nucleus scattering in the local reggeon model with pomeron loops for realistic nuclei

The contribution of the simplest loops for hadron–nucleus scattering cross-sections is studied in Local Reggeon Field Theory with a supercritical pomeron. It is shown that inside the nucleus the supercritical pomeron transforms into a subcritical one, so that perturbative treatment becomes possible. The pomeron intercept becomes complex, which leads to oscillations in the cross-sections.