Fitting DVCS at NLO and beyond

We outline the twist-two analysis of deeply virtual Compton scattering (DVCS)within the conformal partial wave expansion of the amplitude, represented as a Mellin--Barnes integral. The complete next-to-leading order results, including evolution, are obtained in the MS and a conformal factorization scheme. Within the latter, exploiting conformal symmetry, the radiative corrections are evaluated up to next-to-next-to-leading order. Using a new proposed parameterization for GPDs, we study the convergence of perturbation theory and demonstrate for H1 and ZEUS measurements that our formalism is suitable for a fitting procedure of DVCS observables. We comment on a recent claim of a breakdown of collinear factorization and show that a Regge-inspired Q^2 scaling law is ruled out by small x_Bj DVCS data.Comment: 15 pages, 4 figure

Towards a fitting procedure to deeply virtual meson production -- the next-to-leading order case --

Based on the collinear factorization approach, we present a comprehensive perturbative next-to-leading (NLO) analysis of deeply virtual meson production (DVMP). Our representation in conformal Mellin space can serve as basis for a global fitting procedure to access generalized parton distributions from experimental measurements of DVMP and deeply virtual Compton scattering (DVCS). We introduce a rather general formalism for the evaluation of conformal moments that can be developed further beyond the considered order. We also confirm previous diagrammatical findings in the pure singlet quark channel. Finally, we use the analytic properties of the hard scattering amplitudes to estimate qualitatively the size of radiative corrections and illustrate these considerations with some numerical examples. The results suggest that global NLO GPD fits, including both DVMP and DVCS data, could be more stable than often feared.Comment: 125 pages, 7 figures, 8 table

K -> pi gamma decays and space-time noncommutativity

We propose the K -> pi gamma decay mode as a signature of the violation of the Lorentz invariance and the appearance of new physics via space-time noncommutativity.Comment: 3 pages, 1 figure included, version to appear in Phys. Rev.

Tvrde ekskluzivne reakcije i dvo-gluonske komponente η i η ′ mezona

The formalism for treating the leading-twist contributions of the two-gluon Fock components occurring in hard exclusive processes that involve η and η ′ mesons is reviewed. The calculation of the η, η ′–photon transition form factor in next-toleading order in αs, as well as, the analysis of the g ∗ g ∗η ′ vertex and the electroand photoproduction of η, η ′ mesons are presented. Applications of this formalism to other relevant quantities such as glueballs are also discussed.Opisuje se formalizam za izračunavanje doprinosa vodećeg “twista” dvo-gluonskih Fock-ovih komponenti, koje se pojavljuju u tvrdim ekskluzivnim procesima, i koji uključuju η i η ′ mezone. Izlaže se račun η i η ′–γ funkcije strukture prijelaza u redu do vodećeg u razvoju po αs, kao i analiza g ∗ g ∗η ′ verteksa, te elektro- i fotoprodukcije η i η ′ mezona. Također se raspravlja primjena ovog formalizma na druge relevantne veličine poput gluonskih lopti

Tvrde ekskluzivne reakcije i dvo-gluonske komponente η i η ′ mezona

The formalism for treating the leading-twist contributions of the two-gluon Fock components occurring in hard exclusive processes that involve η and η ′ mesons is reviewed. The calculation of the η, η ′–photon transition form factor in next-toleading order in αs, as well as, the analysis of the g ∗ g ∗η ′ vertex and the electroand photoproduction of η, η ′ mesons are presented. Applications of this formalism to other relevant quantities such as glueballs are also discussed.Opisuje se formalizam za izračunavanje doprinosa vodećeg “twista” dvo-gluonskih Fock-ovih komponenti, koje se pojavljuju u tvrdim ekskluzivnim procesima, i koji uključuju η i η ′ mezone. Izlaže se račun η i η ′–γ funkcije strukture prijelaza u redu do vodećeg u razvoju po αs, kao i analiza g ∗ g ∗η ′ verteksa, te elektro- i fotoprodukcije η i η ′ mezona. Također se raspravlja primjena ovog formalizma na druge relevantne veličine poput gluonskih lopti