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     

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     

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.     

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.     

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     

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     

关于软坡密子的张量胶子球的内涵

通过把坡密子的轨迹跟观察到的量子数I^GJ^PC=0⁺2⁺⁺的同位旋标量的张量介子联系起来的关系,研究了坡密子的胶子球内涵.这些介子中有四个满足坡密子的自旋和质量的关系.这些坡密子的后选者可能是混合态.其中,f₂(2220)有极大的胶子球分量.讨论了关于这个介子宽度的实验争论,预言了它的理论下限,也阐明了在pp实验研究中观察不到f₂(2220)原因.     

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.     

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.     

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 relations between the decay constants of pseudoscalar mesons and the residues of the pomeron

The relations between the decay constants of pseudoscalar mesons and the residues of the pomeron are given. Based on these relations, it is shown that the relative scale between the couplings of the zero-mass Nambu-Goldstone bosons to the pomeron is determined by the spontaneous chiral symmetry breaking of the vacuum.     

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     

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.     

Deep inelastic electron-pomeron scattering at HERA

The idea that the pomeron has partonic structure similar to any other hadron has been given strong support by recent measurements of the diffractive structure function at HERA. We present a detailed theoretical analysis of the diffractive structure function under the assumption that the diffractive cross section can be factorized into a pomeron emission factor and the deep inelastic scattering cross section of the pomeron. We pay particular attention to the kinematic correlations implied by this picture, and suggest the measurement of an angular correlation which should provide a first test of the whole picture. We also present two simple phenomenological models for the quark and gluon structure of the pomeron, which are consistent with various theoretical ideas and which give equally good fits to recent measurements by the H1 collaboration, when combined with the pomeron emission factor of Donnachie and Landshoff. We predict that a large fraction of diffractive deep inelastic events will contain charm, and discuss how improved data will be able to distinguish the models.     

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.     

QCD instantons and the soft pomeron

We study the rôle of semiclassical QCD vacuum solutions in high-energy scattering by considering the instanton contribution to hadronic cross sections. We propose a new type of instanton-induced interactions (“instanton ladder”) that leads to the rising with energy cross section σs^Δ of Regge type (the pomeron). We argue that this interaction may be responsible for the structure of the soft pomeron. The intercept Δ>0 is calculated. It has a nonanalytic dependence on the strong coupling constant, allowing a nonsingular continuation into the nonperturbative region. We derive the pomeron trajectory, which appears to be approximately linear in some range of (negative) momentum transfer t, but exhibits a curvature at small t. Possible rôle of instantons in multiparticle production is also discussed.     

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.     

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.