Partonic Structure of the Pomeron in the Modified GLR Equation

The gluon recombination effect in the pomeron is studied by using the modified Gribov-Levin-Ryskin evolution equation. We find that the measured parton distributions in the pomeron can be generated dynamically from a purely gluonic input on assuming a small size for the pomeron.     

Pomeron factorization in general dual models

We demonstrate that in each ghost-free dual model with one minor restriction, there exists a critical dimensionality of space-time in which the pomeron singularity becomes a factorizable Regge pole. In each model when this dimensionality is chosen, the pomeron emerges with twice the intercept and half the slope of the leading secondary (f) trajectory. We explicitly construct the pomeron propagator and the operator coupling the pomeron to the reggeon sector for the general dual model, including the lower-lying negative-G-parity pomeron in the Neveu-Schwarz model. Gauge identities and physical states in the pomeron sector are also investigated. In all of the dual models the pomeron form factors exhibit a generalized f dominance and modified Wu-Yang behavior.     

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.     

Multiple pomeron exchange and final state rescattering

The influence of final state rescattering corrections on multiple pomeron exchange is studied. It is shown in a certain approximation that the multiple exchange of a simple pole pomeron violates the Froissart bound even after the inclusion of these corrections. A self consistent unitarity equation is set up and it is shown that its solution is an expanding black disk. The multiparticle properties of this solution are discussed.     

A numerical study of the small-x behavior of deep inelastic structure functions in QCD

A numerical study of the Gribov-Levin-Ryskin equation for deep inelastic structure functions in the small-x regions is performed. In the first part we study a simplified version which illustrates general features of the solution and also allows to investigate certain analytic properties. In the second part we formulate a more realistic version of the GLR equation and compute its solution, for different input distributions and for different values of the strength of the nonlinearity in the GLR equation. One of the conclusions is that, provided the input distribution is not too flat and the nonlinear coupling is not too small, deviations from the standard evolution may be visible at HERA.     

s-channel unitarity and inclusive distributions in cut reggeon field theory

Unitarity constraints on generalized eikonal diagrams with pomeron interactions are shown to hold in cut reggeon field theory. A non-perturbative proof of the AGK cancellation in this class of diagrams is given for the single-particle inclusive distribution. However, the two-particle distribution turns out to be modified by pomeron interactions in a non-trivial way. An approximate calculation shows that these modifications are crucial for consistency with momentum sum rules.     

J-plane structure of the “cylinder”; slope and intercept of the bare pomeron

We derive and investigate an integral equation for the “cylinder” with full t-dependence. In contrast to the pure pole planar model, the “cylinder” contains, in addition to the bare pomeron pole, also a Reggeon-Reggeon cut. The strongly correlated slope and intercept of the bare pomeron have the correct observed values. We also briefly comment on the concept of “asymptotic planarity”.     

A one-dimensional approximation for the pomeron in the dual unitarity scheme

Using a one-dimensional approximation, the pomeron in the dual unitarity scheme is examined analytically in a multiperipheral cluster model. Clusters have negative short range correlations due to the t_min effect. In dual models, the pomeron has a crossing odd part, especially in B$\text{B}$ and BB scattering. By taking all reggeon loops into account, we show explicitly in our approximation that the crossing-odd part has only lower-lying singularities in the j-plane (typically complex poles with $\text{Re}\text{α?0.2}$) whereas the crossing-even part has the leading singularity at j = α_P (we imposed α_P = 1). The dual unitarity scheme leads to a modified version of the f-dominance of the pomeron. We calculate the SU(3) breaking of the pomeron due to the SU(3) breaking among Regge trajectories without additional assumptions on the SU(3) property of the pomeron.     

Pomeron with a running coupling constant in the nucleus

The running coupling is introduced into the equation for propagation of the pomeron in the nucleus via the bootstrap relation. The resulting equation coincides with the one obtained in the color dipole formalism by summing contributions from quark–antiquark loops, with a general choice of the regularization scheme.     

The pomeron structure in DIS and gluon recombination effects

A formalism for diffractive deep inelastic scattering is presented based on the concept of a pomeron structure function. Assuming the pomeron to be essentially a gluonic object with the small size indicated by its small interaction cross-sections, we show that the QCD evolution of its structure function exhibits large screening corrections due to gluon recombinations at small-χ. With a gluon-to-quark conversion appropriate at small-χ, diffractiveep cross-sections are obtained giving large enough statistics at HERA to distinguish between QCD evolution governed by the conventional Altarelli-Parisi equations and by the non-linear Gribov-Levin-Ryskin equation.     

Triple pomeron vertex in the limit N_c\rightarrow\infty

In the hard pomeron theory with the number of colours the diffractive amplitude obtained in [3] is compared with the results found for in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling. Received: 11 December 1997 / Revised version: 6 February 1998 / Published online: 7 August 1998     

On the Nikolaev-Zakharov-Zoller form for the BFKL pomeron

The equation proposed by N.N. Nikolaev, B.G. Zakharov and V.R. Zoller for the colour dipole cross-section is compared with the BFKL equation for the hard pomeron for theSU(2) colour group. It is demonstrated that for a fixed coupling constant the difference between the two equations is due to a different manner to introduce the gluon mass.     

A multi-pomeron model with zeros in the couplings

The violation of the Froissart bound resulting from repeated exchanges of pomerons in a multi-Regge model is avoided by assuming that some pomeron couplings vanish. The couplings can be chosen such that an input pomeron can produce an output pole coinciding with the input pomeron, and a two-pomeron cut. The main aim is to show that the structure of pomeron couplings can play an important role in calculations involving many pomerons     

f-pole corrections to the critical parameters of the pomeron

A reggeon field theory with two vacuum quantum numbers Regge poles, the pomeron and the f-reggeon is presented. In such a theory only one stable fixed point appears which is sensibly different from that governing a RFT with the pomeron alone. This fact is responsible for the modifications of the critical parameters of the pomeron. In particular, the intercept of the bare pomeron increases and approaches the phenomenological value.     

The dipole picture of high energy scattering,the BFKL equation and many gluon compound states

The relationship and equivalence between the BFKL and dipole equation kernels are investigated by means of explicit calculations in light-cone perturbation theory. A dipole equation, equivalent to the usual equation, for interactions between four reggeized gluons is given in the large N_c limit. The leading trajectory of the four-gluon system is bounded by 2αp − 1 with αp the BFKL pomeron intercept.     

Probing the structure of the pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron. Received: 5 March 1999 / Published online: 3 August 1999     

Avoidance of pomeron-f identity through systematic treatment of overlap contributions to the cylinder

We formulate a unitary equation for the cylinder term in the topoligical expansion which includes a systematic treatment of the overlap configurations to phase space as well as the periphal configurations. If the overlap contributions has Regge pole behavior, then the singlet cylinder plus planar exchange has two output poles which, for suitable values of the parameters, can be identified with a distinct pomeron and shifted f-trajectories.     

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.