Quark-Hadron Duality in Structure Functions

Quark-hadron duality is studied in a systematic way for both the unpolarized and polarized structure functions, by taking into account all the available data in the resonance region.In both cases, a detailed perturbative QCD based analysis of the structure functions integrals in the resonance region is performed: non perturbative contributions are disentangled, and higher twist terms are evaluated. A different behavior between the unpolarized and polarized structure functions at low Q^2 is found.Comment: 5 pages, 4 figure

A Perturbative QCD Based Study of Polarized Nucleon Structure in the Transition Region and Beyond: "Quarks, Color Neutral Clusters, and Hadrons"

A large fraction of the world data on both polarized and unpolarized inclusive $ep$ scattering at large Bjorken $x$ lies in the resonance region where a correspondence with the deep inelastic regime, known as Bloom and Gilman's duality, was observed. Recent analyses of the $Q^2$ dependence of the data show that parton-hadron duality is inconsistent with the twist expansion at low values of the final state invariant mass. We investigate the nature of this disagreement, and we interpret its occurrence in terms of contributions from non partonic degrees of freedom in a preconfinement model.Comment: 5 pages, 1 figure, to be published in the Proceedings of the "3rd International Symposium on the Gerasimov-Drell-Hearn Sum Rule and its Extensions", Editors, J.P. Chen and S. Kuh

Massive higher spins and holography

We review recent progress towards the understanding of higher spin gauge symmetry breaking in AdS space from a holographic vantage point. According to the AdS/CFT correspondence, N=4 SYM theory at vanishing coupling constant should be dual to a theory in AdS which exhibits higher spin gauge symmetry enhancement. When the SYM coupling is non-zero, all but a handful of HS currents are violated by anomalies, and correspondingly local higher spin symmetry in the bulk gets spontaneously broken. In agreement with previous results and holographic expectations, we find that, barring one notable exception (spin 1 eating spin 0), the Goldstone modes responsible for HS symmetry breaking in AdS have non-vanishing mass even in the limit in which the gauge symmetry is restored. We show that spontaneous breaking a' la Stueckelberg implies that the mass of the relevant spin s'=s-1 Goldstone field is exactly the one predicted by the correspondence.Comment: 8 pages, talk presented by M.B. at the "Fourth Meeting on Constrained Dynamics and Quantum gravity" held in Cala Gonone (Sardinia, Italy), September 12-16, 200

Simplifying one-loop amplitudes in superstring theory

We show that 4-point vector boson one-loop amplitudes, computed in ref.[1] in the RNS formalism, around vacuum configurations with open unoriented strings, preserving at least N=1 SUSY in D=4, satisfy the correct supersymmetry Ward identities, in that they vanish for non MHV configurations (++++) and (-+++). In the MHV case (--++) we drastically simplify their expressions. We then study factorisation and the limiting IR and UV behaviour and find some unexpected results. In particular no massless poles are exposed at generic values of the modular parameter. Relying on the supersymmetric properties of our bosonic amplitudes, we extend them to manifestly supersymmetric super-amplitudes and compare our results with those obtained in the D=4 hybrid formalism, pointing out difficulties in reconciling the two approaches for contributions from N=1,2 sectors.Comment: 38 pages plus appendice

A perturbative re-analysis of N=4 supersymmetric Yang--Mills theory

The finiteness properties of the N=4 supersymmetric Yang-Mills theory are reanalyzed both in the component formulation and using N=1 superfields, in order to discuss some subtleties that emerge in the computation of gauge dependent quantities. The one-loop corrections to various Green functions of elementary fields are calculated. In the component formulation it is shown that the choice of the Wess-Zumino gauge, that is standard in supersymmetric gauge theories, introduces ultraviolet divergences in the propagators at the one-loop level. Such divergences are exactly cancelled when the contributions of the fields that are put to zero in the Wess-Zumino gauge are taken into account. In the description in terms of N=1 superfields infrared divergences are found for every choice of gauge different from the supersymmetric generalization of the Fermi-Feynman gauge. Two-, three- and four-point functions of N=1 superfields are computed and some general features of the infrared problem are discussed. We also examine the effect of the introduction of mass terms for the (anti) chiral superfields in the theory, which break supersymmetry from N=4 to N=1. It is shown that in the mass deformed model no ultraviolet divergences appear in two-point functions. It argued that this result can be generalized to n-point functions, supporting the proposal of a possible of use of this modified model as a supersymmetry-preserving regularization scheme for N=1 theories.Comment: 41 pages, LaTeX2e, uses feynMP package to draw Feynman diagram

On the spectrum of AdS/CFT beyond supergravity

We test the spectrum of string theory on AdS_5 x S^5 derived in hep-th/0305052 against that of single-trace gauge invariant operators in free N=4 super Yang-Mills theory. Masses of string excitations at critical tension are derived by extrapolating plane-wave frequencies at g_{YM}=0 down to finite J. On the SYM side, we present a systematic description of the spectrum of single-trace operators and its reduction to PSU(2,2|4) superconformal primaries via a refined Eratostenes' supersieve. We perform the comparison of the resulting SYM/string spectra of charges and multiplicities order by order in the conformal dimension \Delta up to \Delta=10 and find perfect agreement. Interestingly, the SYM/string massive spectrum exhibits a hidden symmetry structure larger than expected, with bosonic subgroup SO(10,2) and thirty-two supercharges.Comment: 28 pages, LaTeX2

In-Medium Properties of Hadrons

A diverse experimental program for the study of the photoproduction of mesons off nuclei has been carried out - and is still running - at the Mainz MAMI and Bonn ELSA electron accelerators with the TAPS, Crystal Barrel, and Crystal Ball calorimeters. It is motivated as a detailed study of the in-medium properties of hadrons and the meson - nucleus interactions. Typical examples for the in-medium behavior of vector mesons ($\omega$), scalar mesons ($\sigma$), and nucleon resonances (P$_{33}$(1232), S$_{11}$(1535), D$_{15}$(1520)) are discussed. Special attention is paid to meson - nucleus final state interactions.Comment: Proceedings of the Meson2006 IX Int. Workshop on Production, Properties and Interaction of Mesons, Cracow, Poland 09 - 14 June, 2006, to be published in Int. J. Mod. Phys.

Complications of regional citrate anti-coagulation for CRRT: an observetional study

Introduction Regional citrate anticoagulation (RCA) is the recommended anticoagulation modality for continuous renal replacement therapy (CRRT). RCA was associated with a low rate of complications in randomized controlled trials. However, little is known about the type and rate of complications in real life. We sought to describe complications associated with RCA in comparison with those associated with heparin anticoagulation. Methods In our institution, RCA has been the default anticoagulation modality for CRRT in all patients without contra-indications since 2013. We have retrospectively reviewed all consecutive patients who received CRRT between January and December 2016 in our institution. For each CRRT session, we have assessed circuit duration, administered dose as well as therapy associated complications. Those parameters were compared according to whether the circuit was run in continuous veno-venous hemodialysis (CVVHD) mode with RCA or continuous veno-venous hemofiltration (CVVH) mode with heparin anticoagulation. Results We analyzed 691 CRRT sessions in 121 patients. Of those 400 (57.9%) were performed in CVVHDRCA mode and 291 (42.1%) in CVVH-Heparin Mode. Compared with CVVH-Heparin mode, CVVHDRCA mode was associated with a longer circuit lifespan (median duration 54.9 (IQR 44.6) vs 15.3 hours (IQR 22.4), p<0.0001).). It was associated with a higher rate of metabolic acidosis (77 (20.2%) vs 18 (7.2%) (p<0.0001), alkalosis 186 (48.7%) vs 43 (17.1%), (p=0.0001) and hypocalcemia (96 (25.07%) vs 26 events (10.79%), (p<0.0001). However, the majority of these alterations were of benign or moderate severity. Only one possible citrate intoxication was observed. Conclusions CVVHD-RCA was associated with a much longer circuit life but an increased rate of minor metabolic complications, in particular acid-base derangements. Some of these complications might have been prevented by therapy adaptation. Medical and nursing staff education is of major importance in the implementation of a RCA protocol