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     

Conformally invariant pomeron interaction in perturbative QCD with large Nc

An effective non-local quantum field theory is constructed, which describes the interaction of pomerons in high-colored QCD. The theory includes both splitting and merging triple pomeron vertexes and diagrams with pomeronic loops. The Schwinger–Dyson equations for the ‘physical’ pomeron are written. Conformal invariance allows one to reduce the theory to the old-fashioned Gribov pomeron theory with an infinite number of pomerons, one of which is supercritical.     

Loops in the reggeon model for <Emphasis Type="Italic">hA</Emphasis> scattering

The contribution of the simplest loops is studied in the local reggeon field theory with a supercritical pomeron in nuclear matter. It is shown that the latter transforms the supercritical pomeron into a subcritical one. Renormalization of the intercept and difficulties related to the fact that the renormalised intercept is complex are discussed. Numerical results with the conventional parameters are reported.     

The Pomeron in Closed Bosonic String Theory

We review the features of the pomeron in the S-matrix theory and in quantum field theory. We extend those general properties to the pomeron of closed bosonic string theory in a Minkowskian background. We compute the couplings of the pomeron to the first few mass levels of closed bosonic string states in flat space. We recognize the deviation from the linearity of the Regge trajectories in a five dimensional anti De Sitter background.     

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.     

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     

On the multipomeron exchange and the BKP equation in the high colour limit

The interaction of reggeized gluons is discussed in the high-colour limit. It is argued that the dominant contributions from the diagrams with a topology of a cylinder sum into a single BFKL pomeron. It is also shown that the BKP equation should be supplemented with terms which change the number of gluons, after which it can be solved in a trivial manner. In the high energy limit the theory reduces to that of noninteracting BFKL pomerons.     

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     

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.     

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.     

One-dimensional quantum theory of the pomeron

The scattering amplitude, originated by the sum over all multi-pomeron exchanges, is evaluated in the zero-slope limit by solving a one-dimensional quantum field theory. In the classical limit, the theory gives back the tree-diagram results obtained in a preceding paper. The constant cross sections obtained in that case for a pomeron with intercept larger than one, are modified only at ultra-asymptotic energies by quantum effects. In the one-dimensional theory, this modification gives rise to cross sections behaving as s^?ΔE where ΔE is a small quantity generated by a tunnel effect.     

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.     

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.     

Existence of a phase transition in reggeon field theory in two transverse dimensions

We show that a reggeon field theory, in the physical number of dimensions, with a linear bare trajectory and a constant triple-pomeron coupling, undergoes a phase transition as the bare pomeron intercept is increased through a certain critical value.     

Antishadowing contribution to the pomeron structure function

In a particular model of the pomeron, its gluon and quark distributions are subject to anti-shadowing, as described by a modified GLR equation recently derived. Inclusion of antishadowing cures the problem of momentum nonconservation previously existing in the GLR equation. A possible outcome of a measurement of the pomeron structure function at HERA is shown in case of DGLAP, GLR and modified GLR parton dynamics.     

The problem of the relation between double pomeron exchange in inclusive and exclusive experiments

The pionization region of the inclusive single-particle spectrum is accounted for by double pomeron exchange in the absorptive part of a six-point amplitude. In this paper a multiperipheral model for the six-point amplitude with double pomeron exchange is used for continuation by crossing and analyticity to the physical region of the exclusive two particle → four particle production process. The cross section for π^? p → π^?(π⁺π^?)p in the double-Regge region is then calculated and compared with the experimental analysis of Lipes, Zweig and Robertson which sets an upper bound to the strength of the double pomeron exchange coupling. This upper bound, coupled with the model for continuation to the inclusive cross section, is shown to give too small a magnitude for the double pomeron exchange in the pionization region. Further avenues for investigation are discussed.     

Saddle point analysis of pomeron singularities in Polyakov's string theory

A saddle-point analysis of Polyakov's string theory is carried out where the Liouville action is defined on surfaces with two disjoint boundaries, (the cylinder topology). This topology is appropriate for probing the closed string excitations. In a saddle point approach, a family of pomeron singularities having a Regge slope half of the ordinary particle trajectories is identified. However, a difficulty with the factorization property arises.     

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     

A theory of dual massive strings

A theory of relativistic strings with non-vanishing mechanical mass is developed. The theory involves the usual massless strings, and the main features of the massless theory are retained so that the system is dual and ghost-free. Some new features appear especially in the mass spectrum of the pomeron sector. The mode with Neveu-Schwarz spin is also considered.