Instantons, diquarks and non-leptonic weak decays of hyperons

This work is devoted to the study of the non-perturbative contributions in non-leptonic hyperon decays. We show that the instanton-induced 't Hooft interaction can naturally explain the Delta I=1/2 rule, by generating quark-diquark clustering inside octet baryons. We compute P-wave and S-wave amplitudes in the Instanton Liquid Model (ILM), and find good agreement with experiment. We propose a model-independent procedure to test on the lattice if the leading quark-quark attraction in the 0^+ anti-triplet channel responsible for diquark structures in hadrons is originated by the interaction generated by quasi-classical fields or it is predominantly due to other perturbative and/or confining forces.Comment: Final version to appear on PR

Instantons, Chiral Dynamics and Hadronic Resonances

We use the Interacting Instanton Liquid Model (IILM) as a tool to study the role played by the chiral interactions in the lowest-lying vector and axial vector meson resonances. We find that narrow a1 and rho meson resonances can be generated by instanton-induced chiral forces, even in the absence of confinement. In the IILM, these hadrons are found to have masses only about 30% larger than the experimental value and small width <10-50 MeV. This result suggests that chiral interactions are very important in these systems and provide most of their mass. We explore the decaying patterns of the rho meson, in the absence of confinement. We argue that, in our model where only chiral forces are switched on, this meson decays dissociating into its quark anti-quark constituents

Are There Diquarks in the Nucleon?

This work is devoted to the study of diquark correlations inside the nucleon. We analyze some matrix elements which encode information about the non-perturbative forces, in different color anti-triplet diquark channels. We suggest a lattice calculation to check the quark-diquark picture and clarify the role of instanton-mediated interactions. We study in detail the physical properties of the 0+ diquark, using the Random Instanton Liquid Model. We find that instanton forces are sufficiently strong to form a diquark bound-state, with a mass of ~500 MeV, which is compatible with earlier estimates. We also compute its electro-magnetic form factor and find that the diquark is a broad object, with a size comparable with that of the proton.Comment: Final version, accepted for publication on Phys. Rev.

Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions

In this paper we address the adequacy of various approximate methods of including Coulomb distortion effects in (e,e') reactions by comparing to an exact treatment using Dirac-Coulomb distorted waves. In particular, we examine approximate methods and analyses of (e,e') reactions developed by Traini et al. using a high energy approximation of the distorted waves and phase shifts due to Lenz and Rosenfelder. This approximation has been used in the separation of longitudinal and transverse structure functions in a number of (e,e') experiments including the newly published 208Pb(e,e') data from Saclay. We find that the assumptions used by Traini and others are not valid for typical (e,e') experiments on medium and heavy nuclei, and hence the extracted structure functions based on this formalism are not reliable. We describe an improved approximation which is also based on the high energy approximation of Lenz and Rosenfelder and the analyses of Knoll and compare our results to the Saclay data. At each step of our analyses we compare our approximate results to the exact distorted wave results and can therefore quantify the errors made by our approximations. We find that for light nuclei, we can get an excellent treatment of Coulomb distortion effects on (e,e') reactions just by using a good approximation to the distorted waves, but for medium and heavy nuclei simple additional ad hoc factors need to be included. We describe an explicit procedure for using our approximate analyses to extract so-called longitudinal and transverse structure functions from (e,e') reactions in the quasielastic region.Comment: 30 pages, 8 figures, 16 reference

new route for tizanidine administration: a pharmacokinetics and light microscope autoradiography study

Spasticity could represent a complication of several central nervous system (CNS) disorders. Multiple sclerosis and painful paroxysmal syndromes (e.g. trigeminal neuralgia) are pathologies in which anti-spastic drugs are used to a greater extent . Baclofen, tizanidine (TIZ), benzodiazepines, dantrolene, and, more recently, gabapentin are the pharmacological agents more widely used. Baclofen, TIZ, benzodiazepines, gabapentin, clonidine but not dantrolene are active on CNS. The alpha2 adrenoceptor agonist TIZ is one of the most eff ective and largely used anti-spastic drugs. Oral treatment is the only route of anti-spastics administration, although it may cause problems of bioavailability and/or compliance in spastic patients with impaired deglutition. This study was designed to assess the possibility of develop a new route of administration of TIZ and to identify its targets in the spinal cord. New Zealand rabbits were treated with oral (OR , n=6), intramuscular (IM, n=6) or intranasal (IN, n=6) TIZ (3.2 mg/kg/day). Plasma concentration was measured by HPLC on samples collected at 0, 30, 60, 90, 120 and 480 min after treatment. Curves of average concentrations of TIZ vs. time were constructed. In plasma, TIZ reached a peak between 45-65 min after administration. Cmax was in the range of 268.33–1213.64 ng/ml for IM treatment, of 73.95–135.92 ng/ml for IN treatment and of 16.86–857.25 ng/ml for OR treatment. After pharmacokinetic studies, diff erent spinal cord tracts were removed and used for radioligand binding assay and autoradiography. Using [3H]-RX821002 ([3H]-RX) (0.1-14nM), the Kd and Bmax for every spinal cord segment were calculated. The non-specifi c binding was obtained with 100μM of (-)-epinephrine. [3H]-RX sites were accumulated in the superfi cial laminae of dorsal horn. Dense [3H]-RX binding in control was seen over the superfi cial dorsal horn (laminae I-II) and centrally located lamina X. The ventral horn showed moderate levels of binding. [3H]-RX was displaced after TIZ treatment using diff erent administration routes. The heaviest accumulation of silver grains (lowest displacement of TIZ) occurred after OR administration of the compound, the lowest after IM administration. These results suggest that both IM and IN administration of TIZ may represent routes of administration of the drug alternative to the OR one. Considering predictable adverse eff ects of IM treatment, the IN administration could represent the elective route to administrate this kind of drugs

Meson exchange and nucleon polarizabilities in the quark model

Modifications to the nucleon electric polarizability induced by pion and sigma exchange in the q-q potentials are studied by means of sum rule techniques within a non-relativistic quark model. Contributions from meson exchange interactions are found to be small and in general reduce the quark core polarizability for a number of hybrid and one-boson-exchange q-q models. These results can be explained by the constraints that the baryonic spectrum impose on the short range behavior of the mesonic interactions.Comment: 11 pages, 1 figure added, expanded discussio

Characterisation of the secondary-neutron production in particle therapy treatments with the MONDO tracking detector

Particle Therapy (PT) is a non-invasive technique that exploits charged light ions for the irradiation of tumours that cannot be effectively treated with surgery or conventional radiotherapy. While the largest dose fraction is released to the tumour volume by the primary beam, a non-negligible amount of additional dose is due to the beam fragmentation that occurs along the path towards the target volume. In particular, the produced neutrons are particularly dangerous as they can release their energy far away from the treated area, increasing the risk of developing a radiogenic secondary malignant neoplasm after undergoing a treatment. A precise measurement of the neutron flux, energy spectrum and angular distributions is eagerly needed in order to improve the treatment planning system software, so as to predict the normal tissue toxicity in the target region and the risk of late complications in the whole body. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project is dedicated to the characterisation of the secondary ultra-fast neutrons ([20-400] MeV energy range) produced in PT. The neutron tracking system exploits the reconstruction of the recoil protons produced in two consecutive (n, p) elastic scattering interactions to measure simultaneously the neutron incoming direction and energy. The tracker active media is a matrix of thin squared scintillating fibers arranged in orthogonally oriented layers that are read out by a sensor (SBAM) based on SPAD (Single-Photon Avalanche Diode) detectors developed in collaboration with the Fondazione Bruno Kessler (FBK)

Nonperturbative versus perturbative effects in generalized parton distributions

Generalized parton distributions (GPDs) are studied at the hadronic (nonperturbative) scale within different assumptions based on a relativistic constituent quark model. In particular, by means of a meson-cloud model we investigate the role of nonperturbative antiquark degrees of freedom and the valence quark contribution. A QCD evolution of the obtained GPDs is used to add perturbative effects and to investigate the GPDs' sensitivity to the nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 17 pages, 10 figures; submitted to Phys. Rev.