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

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

Recovery and reuse of abandoned buildings for student housing: A case study in Catania, Italy

Over the past 15 years, housing supply for university students has increased significantly given the considerable attention provided by national institutions on the issue of student housing. In Italy, however, only approximately 4% of students live in university residences. Since 2001, interventions on existing buildings have accounted for approximately 60% of the overall measures proposed for new university residences; these interventions comprise most of the available public economic resources. The possibility of recovering and reusing existing buildings for university residences is remarkable for the city of Catania because most of the students are enrolled in university courses located within the historic city center. Moreover, abandoned buildings are currently a significant part of the city׳s architectural heritage. This research aims to develop an articulated and integrated set of frameworks to support the various phases of the design process for recovering and then reusing existing buildings as university residences. The proposed approach applies existing dimensional standards and environmental sustainability principles to a constructed building using traditional techniques. Keywords: University residences, Historic center, Recovery, Reuse, Refurbishment, Retrofi

Multiloop String Amplitudes with B-Field and Noncommutative QFT

The multiloop amplitudes for the bosonic string in presence of a constant B-field are built by using the basic commutation relations for the open string zero modes and oscillators. The open string Green function on the annulus is obtained from the one loop scattering amplitude among N tachyons. For higher loops, it is necessary to use the so called three Reggeon vertex, which describes the emission from the open string of another string and not simply of a tachyon. We find that the modifications to the three (and multi) Reggeon vertex due to the B-field only affect the zero modes and can be written in a simple and elegant way. Therefore we can easily sew these vertices together and write the general expression for the multiloop N-Reggeon vertex, which contains any loop string amplitude, in presence of the B-field. The field theory limit is also considered in some examples at two loops and reproduces exactly the results of a noncommutative scalar field theory.Comment: Latex. 27 pages. 9 figures v2: typos corrected, references added; v3: ref. added, version to appear in NP

Synopsis of a Treasure. A Transdisciplinary Study of Medieval Gold Workings Biographies

The article aims to show how a transdisciplinary approach can contribute to a better understanding of the composite biography of a precious object. The study focuses on the Cintola del Duomo (Museum of the Opera del Duomo, Pisa), one of the most famous objects in the history of goldsmithing, both for its exceptional manufacturing quality and for its devotional value. For a long time, the Cintola was considered a fragment of a long garland – decorated with precious stones, enamel, and silver plates – that was displayed on the façade of the Cathedral on certain days of the liturgical calendar. Detailed historical studies suggested that the garland was lost in the early 1300s, while the object now in the museum is more likely to be a reconstruction, decorated with ancient and modern gems. In situ diagnostic campaigns were carried out on the garland using portable Raman spectroscopy (i-Raman, B&W Tek) and portable X-Ray fluorescnece (XRF) (Elio, Bruker) to reveal the identity of the gems and enamels preliminarily studied by gemmological analysis. The combination of analytical techniques made it possible to better outline the complex history of the artefacts. The analysis provided information on the identity of the gems, proposing an interesting question about their possible relationship with the crown of Henry VII of Luxembourg (in the same museum). The study includes aspects related to the materiality of the objects, revealing the socio-cultural context in which the object was produced and supporting its recontextualisation in the museum as a symbolic representation of the past

Twisted determinants on higher genus Riemann surfaces

We study the Dirac and the Laplacian operators on orientable Riemann surfaces of arbitrary genus g. In particular we compute their determinants with twisted boundary conditions along the b-cycles. All the ingredients of the final results (including the normalizations) are explicitly written in terms of the Schottky parametrization of the Riemann surface. By using the bosonization equivalence, we derive a multi-loop generalization of the well-known g=1 product formulae for the Theta-functions. We finally comment on the applications of these results to the perturbative theory of open charged strings.Comment: LaTeX, 26 pages,v3: typos correcte