Small-angle scattering on a system of magnetic and electric charges

The generalization of the conformal scattering method for small-angle scattering processes involving magnetic monopoles and ordinary charges is constructed. Using this generalization we show that introducing of magnetic charges corresponds to analytical continuation of the eikonal amplitude in the complex charge plane (the imaginary part is proportional to the magnetic charge). We calculate explicitly the eikonal amplitude for scattering on a dyon and two monopoles in terms of confluent hypergeometric functions. The singularities of the corresponding amplitudes (focal points) are studied in details.Comment: 15 pages. 3 figures. Latex with epsf.sty use

DVCS amplitude in the parton model

We compute amplitude of deeply virtual Compton scattering in the parton model. We found that the amplitude up to the accuracy O(1/Q) depends on new skewed parton distributions (SPD's). These additional contributions make the DVCS amplitude explicitly transverse.Comment: New spin sum rules for twist-3 SPD's are added. Discussion of 1/Q behaviour of twist-3 contributions is correcte

DVCS on the nucleon : study of the twist-3 effects

We estimate the size of the twist-3 effects on deeply virtual Compton scattering (DVCS) observables, in the Wandzura-Wilczek approximation. We present results in the valence region for the DVCS cross sections, charge asymmetries and single spin asymmetries, to twist-3 accuracy.Comment: 20 pages, 6 figure

Probing generalized parton distributions in pi N -> l+ l- N

We study the exclusive reactions pi- p -> l+ l- n and pi+ n -> l+ l- p$ in view of possible future experiments with high-intensity pion beams. For large invariant mass of the lepton pair l+ l- and small squared momentum transfer to the nucleon these are hard-scattering processes providing access to generalized parton distributions. We estimate the cross section for these reactions, explore their connection with the pion form factor, and discuss the role they can play in improving our understanding of the relevant reaction mechanisms.Comment: 13 pages, 5 figure

Kinematical twist-3 effects in DVCS as a quark spin rotation

We point out that the kinematical twist-3 contributions to the DVCS amplitude, required to restore electromagnetic gauge invariance of the twist-2 amplitude up to O(t/q^2), can be understood as a spin rotation applied to the twist-2 quark density matrix in the target. This allows for a compact representation of the twist-3 effects, as well as for a simple physical interpretation.Comment: 4 pages, revtex, 3 eps figures included using eps

Twist-3 contribution to the γ∗γ→ππ\gamma^*\gamma\to \pi\pi amplitude in the Wandzura-Wilczek approximation

We have calculated the Wandzura-Wilczek contribution to the twist-3 part of $\gamma^*\gamma\to 2\pi$ amplitude. It describes interaction of the longitudinally polarized virtual photon with the real one, and it is suppressed by 1/Q, where $Q^2$ is the virtuality of the $\gamma^*$, as compared to the twist-2 contribution. We have found that, in the Wandzura-Wilczek approximation, factorization applies to the twist-3 amplitude.Comment: 13 pages, 4 figure

Linking generalized parton distributions to constituent quark models

The link between the nucleon generalized parton distributions and the non-diagonal one-body density matrix in momentum space is studied. Attention is focussed on the region where quark generalized parton distributions (GPD's) describe emission and reabsorption of a single active quark by the target nucleon. The correct covariant connection with wave functions used in any constituent quark model is established. Results obtained with different constituent quark models are presented for the unpolarized quark GPD's.Comment: 2 new figures included and references added, conclusions unchanged. Version to appear in Nucl. Phys.

Helicity skewed quark distributions of the nucleon and chiral symmetry

We compute the helicity skewed quark distributions $\widetilde{H}$ and $\widetilde{E}$ in the chiral quark-soliton model of the nucleon. This model emphasizes correctly the role of spontaneously broken chiral symmetry in structure of nucleon. It is based on the large-N_c picture of the nucleon as a soliton of the effective chiral lagrangian and allows to calculate the leading twist quark- and antiquark distributions at a low normalization point. We discuss the role of chiral symmetry in the helicity skewed quark distributions $\widetilde{H}$ and $\widetilde{E}$. We show that generalization of soft pion theorems, based on chiral Ward identities, leads in the region of -\xi < x < \xi to the pion pole contribution to $\widetilde{E}$ which dominates at small momentum transfer.Comment: 22 pages, 5 figure

Assessment of human influenza pandemic scenarios in Europe

The response to the emergence of the 2009 influenza A(H1N1) pandemic was the result of a decade of pandemic planning, largely centred on the threat of an avian influenza A(H5N1) pandemic. Based on a literature review, this study aims to define a set of new pandemic scenarios that could be used in case of a future influenza pandemic. A total of 338 documents were identified using a searching strategy based on seven combinations of keywords. Eighty-three of these documents provided useful information on the 13 virus-related and health-system-related parameters initially considered for describing scenarios. Among these, four parameters were finally selected (clinical attack rate, case fatality rate, hospital admission rate, and intensive care admission rate) and four different levels of severity for each of them were set. The definition of six most likely scenarios results from the combination of four different levels of severity of the four final parameters (256 possible scenarios). Although it has some limitations, this approach allows for more flexible scenarios and hence it is far from the classic scenarios structure used for pandemic plans until 2009