Light cone,Regge contributions and large-angle scattering

The asymptotic behaviour of various three-particle vertices involving reggeons far off-mass-shell, and that of various exclusive reactions is found by using the light-cone algebra of the local and bilocal operators and supposing that the Regge contributions survive in the amplitude in the limit of large momentum transfer. The scaling behaviour (29), (34) is obtained in this way for the exclusive amplitudes. Besides, the asymptotic behaviour of hadronic form factors is obtained. The asymptotic behaviour of Regge-cut contributions and the region of applicability of the scaling behaviour (29) are found for the 2 → 2 amplitude. The relations between the dispersion contributions, Regge contributions, and those of quark diagrams, as well as the role of the signature are discussed. Predictions are given for the energy and the angular distributions for a number of two-particle reactions.     

Regge asymptotics of scattering with flavour exchange in QCD

We investigate the dynamical possibility for the formation of a transient new coherent condition of matter in high-energy hadronic collisions. The coherent bosonic amplitude is characterized by a non-zero mementum and is sustained byP-wave interactions of quasi-pions in a dense fermionic medium. We make quantitative estimates of several essential properties: the condensate momentum and the fermionic density, the zize of the coherent amplitude and the negative energy density contributed by the condensate, a characteristic proper time for the system to exist prior to breakdown into a few pions, and a characteristic extension of the system over the plane perpendicular to the collision axis. These quantities then allow us to make definite estimates of new signals: a few pions with anomalously small transverse momenta <-50 mev/c;=" and=" a=" possible=" anomalous=" bremsstrahlung=" of=" very=" soft=" photons=" with=" characteristic=" transverse=" momenta=" as=" low=" as=" about=" 4=">     

Regge asymptotics of scattering amplitudes in the logarithmic approximation of QCD

The method of separation is applied to the calculation of scattering amplitudes in the Regge region. The method allows to represent the nonladder contributions in a simple form. The result for the amplitude with quark-antiquark exchange and positive signature is discussed.     

Spectrum and Regge trajectories in QCD

Starting in the 1960s, an active group of physicists under the guidance of Prof. K.A. Ter-Martirosyan began creating the theory of high-energy processes in QCD. From the beginning, the key element of this theory is the notion of Regge trajectories and, in particular, of the Pomeron trajectory, which have been introduced phenomenologically. In this talk, I review the problem of the spectrum and Regge trajectories as it can be derived from nonperturbative QCD dynamics.     

Issues in large-angle scattering

We analyze phenomenologically several models for the high-energy scattering of hadrons through fixed, large angles. The emphasis is on trying to isolate and understand those aspects of hadronic forces which are important at large angles. We review the fixed-angle-lower bounds derived from analyticity and discuss how simple geometrical concepts can be used to guide our extrapolation of cross sections away from the forward and backward peaks into the large-angle region. This extrapolation is important in understanding whether or not we need a new, hard component of the hadronic force to interpret the data. We try to isolate the important features of dual models, statistical models, and constituent models and to clarify the possibility of experimental distinction between these approaches.     

Regge poles in multiparticle scattering amplitudes

A study is made of the high-energy limits of multi-particle scattering amplitudes in a φ³ theory. A limited set of chekerboard diagrams dominate the asymptotic behavior .The diagrams sum to produce Regge poles. If N is the number of particles bound together, the trajectory functions of the leading Regge poles are given by α(N)=? (2N ? 3) +g²8π²m². Comparison is made with the generalized multiperipheral model of Auerbach, Aviv, Sugar and Blankenbecler in which the corresponding trajectories have the form α(N)=a?bN+cN².     

Self-intersecting Regge trajectories in multi-channel scattering

We present a simple direct method for calculating Regge trajectories for a multichannel scattering problem. The approach is applied to the case of two coupled Thomas-Fermi type potentials, used as a crude model for electron-atom scattering below the second excitation threshold. It is shown that non-adiabatic interaction may cause formation of loops in Regge trajectories. The accuracy of the method is tested by evaluating resonance contributions to elastic and inelastic integral cross sections.     

Regge theory and statistical mechanics

An interesting connection between the Regge theory of scattering, the Veneziano amplitude, the Lee–Yang theorems in statistical mechanics and nonextensive Renyi entropy is addressed. In this scheme the standard entropy and the Renyi entropy appear to be different limits of a unique mathematical object. This framework sheds light on the physical origin of nonextensivity. A non-trivial application to spin glass theory is shortly outlined.     

Short distance Regge singularities. Renormalized gluon ladder in QCD

It is shown that the renormalized gluon ladder gives rise to an accumulation of Regge poles at j = +1. This approximation is obtained by reordering the perturbation expansion of the Bethe-Salpeter kernel using the renormalization group. The existence of this accumulation is shown to be independent of the gauge. The relevance of this result for the problem of the Pomeron is discussed briefly.     

Hard pair production in large-angle Bhabha scattering

The cross section of hard pair production in large-angle Bhabha scattering is calculated in the leading and next-to-leading logarithmic approximations. Eight regions of the collinear kinematics, when the final particles imitate a process of the 2 → 2 type, and three semicollinear regions, when the final particles imitate a process of the 2 → 3 type, are considered. Analytical formulae for differential cross sections are presented.     

Ambiguities in Regge analyses of backward scattering

Ambiguities in Regge analyses of backward scattering due to the possibility of $\text{u}$ dependence in trajectory and residue functions of fermion Regge poles are investigated. Experiments to clarify the ambiguities are suggested. Also an intrinsic difficulty in separating exchanges of opposite parity is discussed.     

Summation of partial waves for large-angle scattering

For large-angle elastic scattering different methods of summing partial wave amplitudes are investigated for their accuracy and simplicity of computation. It is found that among the approximations considered, the method of expanding the T-matrix in terms of the weighted orthogonal polynomials proposed by Brysk is the most accurate way of calculating the scattering amplitude in the backward direction. If the two-particle interaction is assumed to be a Yukawa potential, then the lth partial sum of the T-matrix with the weighted polynomials can be expressed as the lth partial sum with the Legendre polynomials and a correction term which depends on the phase shift for the lth partial wave.     

The role of absorption in large-angle elastic scattering

The measurements of energy loss distributions obtained in electron scattering experiments at high momentum transfer are presented for Xe, Ar and methane. The spectra show a large variety of intensity distributions, clearly different from those obtained in measurements at the dipole limit. The fraction of the intensity present in the energy loss distribution compared to the elastic peak is significant, but is in line with the reduction of the elastic cross section due to absorption. It is argued that, if similar effects are present in the condensed phase, they should be dealt with in any quantitative analysis of electron transport in matter, as is often done using Monte Carlo simulations. This argument is worked out in some detail for Reflection Electron Energy Loss Spectroscopy.     

Regge theory for multiparticle amplitudes

The asymptotic behavior of multiparticle scattering amplitudes is discussed and reviewed with an emphasis on the analytic structure of the amplitudes as a function of the channel invariants. Single and multiple asymptotic limits of the Regge and helicity type are defined and a recipe is given for obtaining the asymptotic behavior of amplitudes in these limits controlled by exchanges of factorizable Regge poles and constrained by analyticity requirements. Applications to inclusive cross sections and the decoupling theorems for a pomeron Regge pole are reviewed as illustrative consequences of unitarity for multi-Regge theory. The present understanding of the relationship of cuts in angular momentum to unitarity is also described and suggestions given for further research. An effort has been made to keep the discussion pedagogical, while at the same time providing an entree to the literature.     

Real parts of scattering amplitudes and Regge phenomenology

High energy scattering amplitudes are computed using the Harari model for the imaginary parts and fixed t dispersion relations for the real parts. This procedure induces a corrective term to the real part of the Regge amplitudes whose effects are investigated in π-nucleon and K-nucleon charge exchange reactions.     

Complex Regge poles and high energy scattering data

For the high energy data on σ_tot^pp the proton-proton total cross section, and on ?, the ratio of real to imaginary part of the forward elastic amplitude, including the recent ISR results, an excellent fit is obtained with P, P', ω Regge poles plus a pair of complex conjugate Regge poles. The complex poles describe the possible oscillatory behavior of the quantities σ_tot^pp and ?. The physical meaning of these complex poles and extrapolation to future measurements of the above quantities are discussed.