On c=1c=1 critical phases in anisotropic spin-1 chains

Quantum spin-1 chains may develop massless phases in presence of Ising-like and single-ion anisotropies. We have studied c=1 critical phases by means of both analytical techniques, including a mapping of the lattice Hamiltonian onto an O(2) nonlinear sigma model, and a multi-target DMRG algorithm which allows for accurate calculation of excited states. We find excellent quantitative agreement with the theoretical predictions and conclude that a pure Gaussian model, without any orbifold construction, describes correctly the low-energy physics of these critical phases. This combined analysis indicates that the multicritical point at large single-ion anisotropy does not belong to the same universality class as the Takhtajan-Babujian Hamiltonian as claimed in the past. A link between string-order correlation functions and twisting vertex operators, along the c=1 line that ends at this point, is also suggested.Comment: 9 pages, 3 figures, svjour format, submitted to Eur. Phys. J.

Gauge/string duality and scalar glueball mass ratios

It has been shown by Polchinski and Strassler that the scaling of high energy QCD scattering amplitudes can be obtained from string theory. They considered an AdS slice as an approximation for the dual space of a confining gauge theory. Here we use this approximation to estimate in a very simple way the ratios of scalar glueball masses imposing Dirichlet boundary conditions on the string dilaton field. These ratios are in good agreement with the results in the literature. We also find that they do not depend on the size of the slice.Comment: 5 pages, no figures. References updated. Version published in JHE

Low-Dimensional Spin Systems: Hidden Symmetries, Conformal Field Theories and Numerical Checks

We review here some general properties of antiferromagnetic Heisenberg spin chains, emphasizing and discussing the role of hidden symmetries in the classification of the various phases of the models. We present also some recent results that have been obtained with a combined use of Conformal Field Theory and of numerical Density Matrix Renormalization Group techniques.Comment: To be published in the proceedings of the XIII Conference on "Symmetries in Physics", held in Bregenz (Voralberg, Austria), 21-24/7/2003. Plain LaTeX2e, 4 EPS figure

Reconstructing the ancient urban landscape in a long-lived city: the Asculum Project, combining research, territorial planning and preventative archaeology

The Asculum Project started in 2012 by the Bologna University in agreement with the former Soprintendenza per iBeni Archeologici delle Marche and the Municipality of Ascoli Piceno, mainly as a project of urban archaeology and preventative archaeology in a city which has been inhabited for a very long period of time. A proper integrated methodology and the combination of a wide range of data, including that gathered from geophysical surveys, archaeological digs, historic cartography, bibliographic and archival data, allowed us to reconstruct the cityscape during the Roman Age and its development over the centuries. The understanding of the ancient urban landscape also included a detailed morphological study aimed at the reconstruction of the Roman paleosurface, carried out using data derived from coring samples and stratigraphic digs. In parallel, particular attention was directed to the modern 3D documentation of the historical buildings of the city, by means of laser scanner and the analysis of the stratigraphy of the surviving walls. The new surveys covered, in particular, the still extant Roman buildings, such as the temples incorporated by the churches of San Venanzio and San Gregorio Magno, as well as the Sostruzioni dell’Annunziata. These last acquisitions made it possible to reconstruct the overall layout and urban plan of the town during the Roman Age, as well as to shed new light on the conformation of the ancient landscape at the time of the oldest Piceni settlement. One of the most interesting aspects of the operating practices applied in the project was to reconcile the needs for preservation and research with the aim of a sustainable urban development

FFLO oscillations and magnetic domains in the Hubbard model with off-diagonal Coulomb repulsion

We observe the effect of non-zero magnetization m onto the superconducting ground state of the one dimensional repulsive Hubbard model with correlated hopping X. For t/2 < X < 2t/3, the system first manifests Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) oscillations in the pair-pair correlations. For m = m1 a kinetic energy driven macroscopic phase separation into low-density superconducting domains and high-density polarized walls takes place. For m > m2 the domains fully localize, and the system eventually becomes a ferrimagnetic insulator.Comment: IOP RevTeX class, 18 pages, 13 composite *.eps figure