Charged open strings in a background field and Euler-Heisenberg effective action

This talk is based on work made with L. Magnea and R. Russo. We give an explicit expression of the multiloop partition function of open bosonic string theory in the presence of a constant gauge field strength. The Schottky parametrization allows to perform the field theory limit, which at two-loop level reproduces the Euler-Heisenberg effective action for adjoint scalars minimally coupled to the background gauge field.Comment: To be published in the Proceedings of ICHEMP '05, Marrakech, Morocc

Twisted determinants and bosonic open strings in an electromagnetic field

The bosonization equivalence between the 2-dimensional Dirac and Laplacian operators can be used to derive new interesting identities involving Theta functions. We use these formulae to compute the multiloop partition function of the bosonic open string in presence of a constant electromagnetic field.Comment: 7 pages; Contribution to the proceedings of the 36th International Symposium Ahrenshoop. v2: References adde

Pinching parameters for open (super) strings

We present an approach to the parametrization of (super) Schottky space obtained by sewing together three-punctured discs with strips. Different cubic ribbon graphs classify distinct sets of pinching parameters; we show how they are mapped onto each other. The parametrization is particularly well-suited to describing the region within (super) moduli space where open bosonic or Neveu-Schwarz string propagators become very long and thin, which dominates the IR behaviour of string theories. We show how worldsheet objects such as the Green's function converge to graph theoretic objects such as the Symanzik polynomials in the $\alpha ' \to 0$ limit, allowing us to see how string theory reproduces the sum over Feynman graphs. The (super) string measure takes on a simple and elegant form when expressed in terms of these parameters.Comment: 68 pages, 31 figure

Anyonic Realization of the Quantum Affine Lie Algebras

We give a realization of the quantum affine Lie algebras \uqa and \uqc in terms of anyons defined on a one-dimensional chain (or on a two-dimensional lattice), the deformation parameter $q$ being related to the statistical parameter $\nu$ of the anyons by $q = e^{i\pi\nu}$. In the limit of the deformation parameter going to one we recover the Feingold-Frenkel fermionic construction of undeformed affine Lie algebras.Comment: 8p, LaTeX, subeqn.sty. Also available at http://lapphp0.in2p3.fr/preplapp/psth/anyon_ac.ps.g

Multi-loop open string amplitudes and their field theory limit

JHEP is an open-access journal funded by SCOAP3 and licensed under CC BY 4.0This work was supported by STFC (Grant ST/J000469/1, ‘String theory, gauge theory & duality’) and by MIUR (Italy) under contracts 2006020509 004 and 2010YJ2NYW 00

Electrical and ultraviolet characterization of 4H-SiC Schottky photodiodes

Fabrication and electrical and optical characterization of 4H-SiC Schottky UV photodetectors with nickel silicide interdigitated contacts is reported. Dark capacitance and current measurements as a function of applied voltage over the temperature range 20 °C – 120 °C are presented. The results show consistent performance among devices. Their leakage current density, at the highest investigated temperature (120 °C), is in the range of nA/cm2 at high internal electric field. Properties such as barrier height and ideality factor are also computed as a function of temperature. The responsivities of the diodes as functions of applied voltage were measured using a UV spectrophotometer in the wavelength range 200 nm - 380 nm and compared with theoretically calculated values. The devices had a mean peak responsivity of 0.093 A/W at 270 nm and −15 V reverse bias

Effetti legali e negoziali degli accordi di ristrutturazione dei debiti

Gli effetti legali e gli efffetti negoziali degli accordi di ristrutturazione dei debiti ex art. 182 bis, l.f. Tre norme sull'efficacia. Formazione progressiva della fattispecie e deviazioni patologiche. Dalle trattative all'accordo. Le trattative. II. L'accordo e i suoi rapporti col procedimento. Effetti negoziali ed effetti legali. La "pubblicazione"e i suoi effetti. L' "accordo" come fattispecie: causa unitaria e oggetto "libero". Rilevanza mediata del contratto nella produzione degli effetti legali. Requisiti minimi dell'accordo: forma e parti; unanimit\ue0 e relativit\ue0 dell'accordo; struttura dell'accordo.III. Effetti della conclusione del procedimento. Rigetto dell'omologazione. Omologazione e regolare esecuzione. IV. Patologie negoziali emergenti dopo l'omologazione. Omologazione e vizi dell'accordo. Mancata esecuzione o sopravvenuta "inidoneit\ue0" dell'accordo a garantire il regolare pagamento dei creditori estranei: la risoluzione dell'accordo; rimedi spettanti ai creditori estranei; rapporti fra sopravvenuta dichiarazione di fallimento ed efficacia dell'accordo; modificabilit\ue0 dell'accordo? Omologazione e vizi genetici dell'accordo. V. Effetti dell'apertura del fallimento. Apertura del fallimento. L'esenzione dalla revocatoria fallimentare. Azionabilit\ue0 della revocatoria ordinaria. Impossibilit\ue0 di prededurre la cd. "nuova finanza". Le responsabilit\ue0

The extended conformal theory of Luttinger systems

We describe the recently introduced method of algebraic bosonization of the $(1+1)$-dimensional Luttinger systems by discussing in detail the specific case of the Calogero-Sutherland model, and mentioning the hard-core Bose gas. We also compare our findings with the exact Bethe Ansatz results.Comment: 9 pages, plain Latex file, ,based on a talk given by S. Sciuto at the II International Sakharov Conference on Physics, Moscow, Russia, 20-24 May 9