Shackless on linear absorption models

We examine the fundamental constraints that all Linear Absorption Models must possess, independent of the rescattering amplitude. These constraints are most direct in impact parameter space, where the re-scattering appears simply as a multiplicative factor. It is a crucial test of such models that the ratio of two exchanges — for example vector and tensor exchanges — is completely specified in b-space by the ratio of input Regge pole amplitudes. Amplitude analysis exist for vector π exchange, in π⁻p→π^On. Lacking experimental A₂ tensor amplitudes, we use the Linear Absorption Models constraint to calculate A₂ exchange from ? input, and compare the results with π⁻p→η^On data. Both simplicity and duality assumptions for Regge pole couplings are considered. The results suggest that Linear Absorption Models constraint is not fully consistent with data.     

The structure of t-channel exchanges in KN scattering

Recent phase-shift solutions are used to evaluate KN FESR integrals in order to examine zeros and phases of the t-channel exchange amplitudes in the most model-independent way. The results suggest that the line reversal breaking in KN CEX observed for pL ? 5.5 GeV/c is due to a large EXD breaking component in the A₂ exchange flip amplitude. The ? exchange flip amplitude is well described by a Regge pole amplitude with NWSZ at ?t ≈ 0.5 (GeV/c)². The imaginary parts of ? and ω exchange non-flip amplitudes are both peripheral.     

About ω0-exchange in the (γ, π0) reaction on the proton near threshold

With the amplitudes obtained in the effective lagrangian (BL) and in the dispersion (BDW) methods the new data for the (γ, π⁰) reaction on the proton near threshold are analysed. The inclusion of ω⁰-meson exchange in the BDW amplitude removes the discrepancy with experimental data. The tensor and vector coupling constants which are consistent with the results of other analyses give the value of E₀₊ multipole predicted by the PCAC hypothesis.     

Vector meson production by inelastic scattering of polarized electrons off polarized nucleons

A general analysis of vector meson production by inelastic scattering of polarized electrons (or muons) off polarized nucleons is presented. Cross section and vector meson decay angular distribution are discussed in terms of s-channel helicity amplitudes for natural and unnatural parity exchange. The question of experiments suitable for analyzing the more refined dynamical features of ?⁰-production is discussed in detail. Estimates are given for the effects to be expected from unnatural parity exchange.     

Amplitude analysis of hypercharge exchange reactions

We present a smooth parametrization of the amplitudes for meson-baryon hypercharge exchange reactions which describes well all the data available at present for laboratory momenta above 3 GeV/c. The K_V¹ (K_T¹) amplitudes we find are very similar to the ?(ω) amplitudes, respectively, obtained already by other authors. The SU(3) assumption seems to be well supported by the experimental data.     

Construction of tensor exchange amplitudes in KN and KN CEX reactions

K⁺n charge exchange (CEX) polarization data obtained recently by the Saclay group at CERN are supplemented by differential cross-section data and by information on K^?p CEX, and used to construct tensor exchange non-flip and flip components T₀ and T₁ of the s-channel helicity amplitudes directly from data at 6 GeV/c and for |t| ? 0.9. Vector exchange amplitudes are assumed to be known from πN scattering. The sensitivity of solutions to the uncertainties in the input data is examined in great detail. In general we find a unique solution for all t.We observe new features in the t-structure of non-flip and flip amplitudes. Re T₀Re T₀ have simple zeros at t ≈ ?0.45 and t ≈ ?0.65. Im T₀ has a dip or a double zero at t ≈ ?0.16 and a double zero structure at t ≈ ?0.45. Im T₁ has two simple zeros at t ≈ ?0.45 and t ≈ ?0.70. Violations of weak EXD in both amplitudes correspond to a lower A₂ trajectory by approximately Δα ≈ 0.1. If certain conditions are satisfied by the input data, a discrete ambiguity exists in the solutions for |t| ? 0.55 and this possibility is also carefully examined.     

Exchange ofA 1 andZ 1 (J PC=2−−) mesons in charged pion photoproduction

Finite energy sum rules are evaluated for the amplitudes corresponding to the exchange of theA ₁ and its exchange degenerate partner, theZ ₁ (J ^PC=2^??), in charged pion photoproduction. Both sum rules are roughly compatible with theoretical estimates of these exchanges, and a definiteA ₁ signal found.     

Kaon-nucleon finite energy sum rules revisited

Kaon-nucleon finite energy and continuous moment sum rule integrals are evaluated using recent phase-shift solutions to extract the t-channel exchange amplitudes and the results are compared with Regge pole models. The exchange degeneracy breaking previously observed in the ? and A₂ amplitudes is confirmed, and it is suggested that this may be due to an exotic P₀₁ KN resonance. Regge trajectories are extracted from the integrals and are in good agreement with those found from direct fits to high-energy data.     

Determination of coupling constants from superconvergence sum rules in vector meson — Vector meson scattering

Dynamical relations between masses and coupling constants have been studied using the superconvergent sum rule technique in vector meson — vector meson scattering. Unessential complications due to the spin have been removed by defining a set of 25 KSF invariant amplitudes. Commonly accepted analyticity properties and asymptotics estimated arguing along the line of unitarity then lead to superconvergent sum rules for three amplitudes. Their saturation by one-intermediate-particle contributions in the processesωρ→ ωρ, ωB→ωB andωA ₁→ωA ₁ results in a system of nine coupled equations which have been approximately solved for coupling constants and aρ-ω-B- A ₁ mass sum rule.     

High-energy scattering in a two-dimensional gauge theory

We study high-energy scattering in two-dimensional quantum chromodynamics in the 1/N_colour expansion. To first order, high-energy forward scattering amplitudes are power-behaved with the factorization, signature and exchange degeneracy properties found in dual Regge models. Backward scattering has deviations from naive quark power-counting rules which are related to the form factor and “Regge” behaviours. In the second order of 1/N_colour vacuum exchange diagrams do not give a new Pomeron singularity, but do break exchange degeneracy.     

On W±, Z0, γ self-interactions: High energy behaviour and tree unitarity bounds

We analyze the high-energy behaviour of vector boson scattering amplitudes within the framework of a recently suggested lagrangian model based on global weak isospin symmetry broken by electromagnetism. Requiring vanishing of the most strongly (as s²) rising contribution to vector boson scattering amplitudes leads to vector boson self-interactions dependent on a single parameter, for which the anomalous W^± magnetic moment, κ, can be chosen. Tree unitarity is violated at about 2 TeV for arbitrary κ as in the SU(2)_L × U(1)_Y theory for m_H → ∞. The model is well suited for significant tests of the vector boson sector of the SU(2)_L × U(1)_Y electroweak theory in processes such as e⁺e⁻ → W⁺W⁻.     

An application of dispersion relations to Kaon-nucleon scattering

In this paper we have made predictions for the invariant KN and $\text{K}$N scattering amplitudes in the kinematical region q_lab < 15 GeV/c and 0 >; t > -0.7 (GeV/c)².We have performed a direct fit to medium and high-energy data using a parametrization where the imaginary part of the amplitudes for energies above the phase-shift region is identical with the imaginary part of a Regge-pole amplitude, and the real part of the amplitudes has been obtained from a dispersion relation.The s-channel helicity amplitudes are compared with their counterparts in pion-nucleon scattering and other reactions. Exact exchange degeneracy can not be verified.Also the real part of the amplitudes are compared with the real part of phase-shift solutions. There is a qualitative agreement between these two real parts even though they differ in detail.     

Amplitudes of multichannel scattering on the barrier with a constant height in the scattering direction

The immersing method is applied to solve the N-channel scattering problem. In particular, we consider the particle scattering on a multidimensional potential barrier, which is constant in the scattering direction and arbitrary in the lateral direction. For this case the scattering amplitudes t _m and r _m (m = 1, 2, …, N) are determined. Transition from the obtained formulas to the case of thin potential is performed. For this case analytical expressions of transmission amplitudes t _m and reflection amplitudes r _m are obtained. We show that the product of transmission and reflection amplitudes in the channel m does not depend on the scattering channel. It is assumed that the scattering particle falls on the potential with the longitudinal wave vector k _l corresponding to the channel l.     

On the behavior of the πN partial wave amplitudes ats=0

The behavior of theπN partial wave amplitudes in the limitss→+0 ands→? 0 is related to backward scattering in thes- andt-channel, respectively. Assuming Mandelstam analyticity we prove with the aid of the Phragmen-Lindelöf theorem that the amplitudes for high energy backward scattering inπN→πN andππ→N¯N are equal and therefore dominated by the same exchange mechanism, namely Reggeized Fermion exchange. The dominating Regge trajectory is the Δ_δ-trajectory, and it is shown that theπN partial wave amplitudes diverge fors→±0 as \(s^{ - \alpha \Delta _\delta (0) - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} \) . — Reduced amplitudes are defined which are regular ats=0. — Using recent results ofπN backward scattering real and imaginary part of thes-wave amplitudef ₀₊ ^(?) are calculated in the interval 0≦s≦7.     

Charm Hadrons in Dense Matter

The properties of the D and D _s charmed mesons in normal nuclear matter density are studied within a coupled channel approach using a t-channel vector-meson exchange mechanism as driving force. The in-medium scattering amplitudes are obtained by solving the Lippmann?CSchwinger equation including Pauli blocking effects and medium self-energies in a self-consistent way.     

SU3 comparison of line reversed charge exchange and hyperchange exchange reactions

The recent data at 10.1 GeV/c on the hypercharge reactions π⁺p → K⁺Σ⁺ (1385) and the line reversed processes are compared with the SU₃ related charge exchange processes K⁺n → K^op and K⁺p →K^oΔ⁺⁺ and their line reversed partners in order to study the systematics of line reversal breaking. Allowing for a t- independent SU₃ breaking between charge and hypercharge exchange the data follow the SU₃ relations. We conclude that the line reversal breaking in the hypercharge exchange reactions is in agreement with the breaking in exchange degeneracy (in both flip and non-flip amplitudes) which is observed for the charge exchange processes.     

A relativistic quark model for mesons based on numerical solutions of the Bethe-Salpeter equation

A study is made to determine if the results of the nonrelativistic quark model can be reproduced by a fully relativistic model of deeply bound $\text{spin}\text{-}\text{1}\text{2}$ quarks. It is found that the relativistic model does not reproduce the nonrelativistic results, even when the quarks have nonrelativistic momenta. However, the model is rather successful in accounting for the known properties of mesons.Numerical solutions to the Bethe-Salpeter equation are obtained for pseudoscalar and vector bound states of equal mass quark-antiquark pairs, with either a scalar, pseudoscalar, or neutral vector exchange interaction. The interaction function corresponds to single particle exchange, with the addition of either one or two regulating terms. It is found that the second regulator allows the internal quark momentum to be nonrelativistic, but that the spinor structure of the wave function remains highly relativistic.Only the scalar interaction can account for the observed spectrum of states. The pseudoscalar interaction yields a vector state of lower mass than the pseudoscalar state, and the vector interaction leads to a vector state which lies approximately one quark mass above the pseudoscalar state. The λ quark is taken as slightly heavier than the p and n, and the perturbation treatment of the mass difference leads to a quadratic mass formula.The decay amplitudes for π, K → μν are calculated, and it is found, independent of parameters, that $\text{?}{}_{\mathrm{\pi }}\text{≈ ?}{}_{\mathrm{K}}$ for either a scalar or vector interaction, in agreement with experiment and in contrast with the nonrelativistic model. The amplitudes for ?^o, ω, φ → e⁺e^?, μ⁺μ^? are also calculated, but in this case the ratios (again parameter independent) are in minor discrepancy with experiment.The question of the additivity of quark amplitudes is examined by calculating (with significant restrictions) the magnetic moments of the vector mesons and the amplitudes for magnetic transitions such as ω → π^oγ. The magnetic moments of the vector mesons have the same (trivial) ratios to each other as in the nonrelativistic model, but they are strongly enhanced over the sum of the quark magnetic moments. The amplitude for magnetic transitions, however, is related to the quark magnetic moments in approximately the same ratio as in the nonrelativistic model.The model is also used to obtain parameter dependent predictions for the masses and decay amplitudes. These predictions are not experimentally correct, but are generally well within an order of magnitude for a wide range of the parameters.The most significant defect discovered of the model is the presence of ghost states (the daughters of the vector mesons, with J^PC = 0^+?) with masses of about 2 BeV.     

J-dependence of the twist parameter in dual unitarity

It is pointed out that the twist parameter which governs the breaking of exchange degeneracy, Zweig rule violation, exotic exchange, and the relative production of vector and tensor mesons, is J-dependent. A simple model for this dependence reconciles the smallness of exotic exchange with the large ratio of vector to tensor production, and successfully predicts the sign and magnitude of α_?(0)?α_A2(0).