Wilson Loops and Scattering Amplitudes in Supersymmetric Field and String Theories

The long-standing problem of finding weak-strong coupling interpolating observables for supersymmetric Chern-Simons theories in three dimensions is analysed from the point of view of BPS Wilson loop operators.Analizziamo l'annoso problema della determinazione di funzioni interpolanti tra i regimi di accoppiamento debole e accoppiamento forte in teorie di Chern-Simons supersimmetriche in tre dimensioni dal punto di vista di operatori di Wilson BPS

Development of solvent-casting particulate leaching (SCPL) polymer scaffolds as improved three-dimensional supports to mimic the bone marrow niche

The need for new approaches to investigate ex vivo the causes and effects of tumor and to achieve improved cancer treatments and medical therapies is particularly urgent for malignant pathologies such as lymphomas and leukemias, whose tissue initiator cells interact with the stroma creating a three-dimensional (3D) protective environment that conventional mono- and bi-dimensional (2D) models are not able to simulate realistically. The solvent-casting particulate leaching (SCPL) technique, that is already a standard method to produce polymer-based scaffolds for bone tissue repair, is proposed here to fabricate innovative 3D porous structures to mimic the bone marrow niche in vitro. Two different polymers, namely a rigid polymethyl methacrylate (PMMA) and a flexible polyurethane (PU), were evaluated to the purpose, whereas NaCl, in the form of common salt table, resulted to be an efficient porogen. The adoption of an appropriate polymer-to-salt ratio, experimentally defined as 1:4 for both PMMA and PU, gave place to a rich and interconnected porosity, ranging between 82.1 vol% and 91.3 vol%, and the choice of admixing fine-grained or coarse-grained salt powders allowed to control the final pore size. The mechanical properties under compression load were affected both by the polymer matrix and by the scaffold's architecture, with values of the elastic modulus indicatively varying between 29 kPa and 1283 kPa. Preliminary tests performed with human stromal HS-5 cells co-cultured with leukemic cells allowed us to conclude that stromal cells grown associated to the supports keep their well-known protective and pro-survival effect on cancer cells, indicating that these devices can be very useful to mimic the bone marrow microenvironment and therefore to assess the efficacy of novel therapies in pre-clinical studies

On-shell Recursion in String Theory

We prove that all open string theory disc amplitudes in a flat background obey Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion relations, up to a possible reality condition on a kinematic invariant. Arguments that the same holds for tree level closed string amplitudes are given as well. Non-adjacent BCFW-shifts are related to adjacent shifts through monodromy relations for which we provide a novel CFT based derivation. All possible recursion relations are related by old-fashioned string duality. The field theory limit of the analysis for amplitudes involving gluons is explicitly shown to be smooth for both the bosonic string as well as the superstring. In addition to a proof a less rigorous but more powerful argument based on the underlying CFT is presented which suggests that the technique may extend to a much more general setting in string theory. This is illustrated by a discussion of the open string in a constant B-field background and the closed string on the level of the sphere.Comment: 36 + 9 pages text, one figure, v3: added discussion on relation to old-fashioned factorization, typos corrected, published versio

The generalized cusp in ABJ(M) N = 6 Super Chern-Simons theories

We construct a generalized cusped Wilson loop operator in N = 6 super Chern-Simons-matter theories which is locally invariant under half of the supercharges. It depends on two parameters and interpolates smoothly between the 1/2 BPS line or circle and a pair of antiparallel lines, representing a natural generalization of the quark-antiquark potential in ABJ(M) theories. For particular choices of the parameters we obtain 1/6 BPS configurations that, mapped on S^2 by a conformal transformation, realize a three-dimensional analogue of the wedge DGRT Wilson loop of N = 4. The cusp couples, in addition to the gauge and scalar fields of the theory, also to the fermions in the bifundamental representation of the U(N)xU(M) gauge group and its expectation value is expressed as the holonomy of a suitable superconnection. We discuss the definition of these observables in terms of traces and the role of the boundary conditions of fermions along the loop. We perform a complete two-loop analysis, obtaining an explicit result for the generalized cusp at the second non-trivial order, from which we read off the interaction potential between heavy 1/2 BPS particles in the ABJ(M) model. Our results open the possibility to explore in the three-dimensional case the connection between localization properties and integrability, recently advocated in D = 4.Comment: 53 pages, 10 figures, added references, this is the version appeared on JHE

Analytical Approach to Study the Carbon and Nitrogen Forms in a Tomato-Cultivated Soil Treated with Biochar and Biostimulants

Agro-environmental applications of biochar and biochar in combination with biostimulants in soil applications require a full understanding of the mobility and fate of the carbon and nitrogen fractions. The effects of biochar and biostimulants on forms of nitrogen and carbon in soil during field-scale incubation were investigated by a multi-analytical approach. This work presents the preliminary results of a study conducted on a tomato-cultivated agricultural land treated with low doses of biochar (about 0.1%) and different combinations of biostimulants: Micosat F®, arbuscular mycorrhiza fungi (AMF), and a consortium of Pseudomonas fluorescens, Bacillus sp., and a nitrogen-fixing bacteria (Consortium B). Forms of carbon and nitrogen and their mobility before, during, and after tomato growth, were studied with a combination of techniques that included elemental analysis, adsorption and molecular fluorescence spectroscopy, ion chromatography, and a column leaching test. Due to the low load of biochar and the short period of time, elemental analyses might not be sensitive enough to determine C and N variation in the soil. The study of the dissolved organic carbon (DOC) and nitrogen forms (DN) showed that the treatments performed with biochar and biostimulants affected the mobility of these elements with an overall decrease at the end of tomato growth. The organic carbon is mainly ascribable to humic and fulvic acids, as indicated by spectroscopic analysis. The leaching column test demonstrated that cumulative leached C is about one order of magnitude lower than the DOC. In addition, simulated rain cycles profoundly affected leaching, so it is important to design leaching tests based on local and seasonal weather conditions. Moreover, positive effects were observed in the marketable production of tomato when soil was treated with biochar combined with a mixture of biostimulants