2,674 research outputs found
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 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 being related to the statistical
parameter of the anyons by . 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, âString theory, gauge theory & dualityâ)
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 â 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 â15 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
Algebraic bosonization: the study of the Heisenberg and Calogero-Sutherland models
We propose an approach to treat (1+1)--dimensional fermionic systems based on
the idea of algebraic bosonization. This amounts to decompose the elementary
low-lying excitations around the Fermi surface in terms of basic building
blocks which carry a representation of the W_{1+\infty} \times {\overline
W_{1+\infty}} algebra, which is the dynamical symmetry of the Fermi quantum
incompressible fluid. This symmetry simply expresses the local particle-number
current conservation at the Fermi surface. The general approach is illustrated
in detail in two examples: the Heisenberg and Calogero-Sutherland models, which
allow for a comparison with the exact Bethe Ansatz solution.Comment: 51 pages, plain LaTe
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