A new mechanism of mass protection for fermions

We present a way of protecting a Dirac fermion interacting with a scalar (Higgs) field from getting a mass from the vacuum. It is obtained through an implementation of translational symmetry when the theory is formulated with a momentum cutoff, which forbids the usual Yukawa term. We consider that this mechanism can help to understand the smallness of neutrino masses without a tuning of the Yukawa coupling. The prohibition of the Yukawa term for the neutrino forbids at the same time a gauge coupling between the right-handed electron and neutrino. We prove that this mechanism can be implemented on the lattice.Comment: LATTICE99(Higgs,Yukawa,SUSY), 3 page

The Need for Unification and Harmonization in a Maritime Licensing Standard for Recreational Craft

The objective of this document is to make clear the importance of simplifying the transit of pleasure boats and their skippers safely in the European territory with the foreseeable improvement of the functioning of the internal market. In many European countries recreational skippers are required to have specific training and experience in order to demonstrate their maritime competence. These licenses for navigation allow a recreational vessel to be skippered in each national territory. One of the main objectives of these qualifications is to reduce the number of accidents in recreational boating. Generally speaking, in the European Union, as regards the requirements for the management of pleasure craft, both private and professional, the requirements are very different depending on the member state

Massless Decoupled Doublers: Chiral Yukawa Models and Chiral Gauge Theories

We present a new method for regularizing chiral theories on the lattice. The arbitrariness in the regularization is used in order to decouple massless replica fermions. A continuum limit with only one fermion is obtained in perturbation theory and a Golterman-Petcher like symmetry related to the decoupling of the replicas in the non-perturbative regime is identified. In the case of Chiral Gauge Theories gauge invariance is broken at the level of the regularization, so our approach shares many of the characteristics of the Rome approach.Comment: 11 page

A measure of conductivity for lattice fermions at finite density

We study the linear response to an external electric field of a system of fermions in a lattice at zero temperature. This allows to measure numerically the Euclidean conductivity which turns out to be compatible with an analytical calculation for free fermions. The numerical method is generalizable to systems with dynamical interactions where no analytical approach is possible.Comment: version to be published in Physics Letters

Monte Carlo studies of antiferromagnetic spin models in three dimensions

We study several antiferromagnetic formulations of the O(3) spin model in three dimensions by means of Monte Carlo simulations. We discuss about the vacua properties and analyze the phase transitions. Using Finite Size Scaling analysis we conclude that all phase transitions found are of first orderComment: 4 pages, 2 Postscript figures. Contribution to Lattice '9

Phase diagram and influence of defects in the double perovskites

The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo O_6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.Comment: 4 pages, 3 postscript figures, some errata correcte

Stratigraphy of Late Pleistocene coastal deposits in Northern Spain

Stratigraphical and sedimentological analysis, geological mapping and geochronological dating (luminescence, uranium/thorium, and radiocarbon) were undertaken on Late Pleistocene coastal deposits (raised beaches and periglacial deposits) in north-west Spain. Correlation of the 26 outcrops studied and their geometric relationships allowed the establishment of four stratigraphic units: Unit 1, sandy and gravelly raised beaches located above a rocky abrasion platform 1.5 –3.5 m above the modern mean sea level; Unit 2, matrix-supported breccias of head deposits; Unit 3, muddy peats formed in swamp depressions; and Unit 4, clast-supported conglomerates, breccias, and sands, deposited by intermittent current activity. Thermoluminescence (TL) and infrared-stimulated luminescence dating (IRSL) assigned Unit 1 to OIS 5; Unit 2 to OIS 4/3; and Unit 4 to OIS 3–2. Radiocarbon dating confi rmed the results obtained for Units 2 and 4 and that Unit 3 was contemporaneous with Unit 2. Comparison of these outcrops with others from raised beaches located in the central part of the northern Spanish coast (Cantabria) showed that the Cantabrian sector has been uplifted 2–3 m more than the north-west coast since the Last Interglacial. It is probable that Galicia acted as a hinge line between the uplifting north and the active, faulted atlantic margin of the Iberian Peninsula.En este trabajo se analizan los depósitos del Pleistoceno fi nal en el sector costero del noroeste de la Península Ibérica desde el punto de vista estratigráfi co y sedimentológico. Se han estudiado y correlacionado 26 afl oramientos, lo que ha permitido la diferenciación de cuatro unidades litoestratigráfi cas, cuya edad ha sido obtenida mediante las técnicas de luminiscencia, radiocarbono y uranio/torio. La Unidad 1 corresponde a playas levantadas arenosas y de gravas, que descansan sobre una plataforma de abrasión rocosa situada entre 1,5 y 3,5 metros sobre el actual nivel medio del mar. La Unidad 2 consiste en brechas matriz soportadas originadas como depósitos de ladera y de arroyada al pie de paleopendientes. La Unidad 3, formada por fangos orgánicos y turbas, corresponde a turberas en zonas deprimidas encharcadas. La Unidad 4, que consiste en conglomerados, brechas y arenas, se formó como depósitos aluviales, generalmente en corrientes esporádicas. Las dataciones por luminiscencia (teniendo en cuenta las limitaciones disdel método en este tipo de materiales), indican que la Unidad 1 corresponde al OIS 5, la 2 a los estadios 4 – 3, la 3 es contemporánea de la 2 y la 4 se formó durante los estadios isotópicos 3 – 2. Las dataciones de radiocarbono confi rman los resultados obtenidos para las unidades 2 y 4. La comparación de estos afl oramientos con las playas levantadas de Oyambre y Merón en Cantabria, muestran que este último sector ha sufrido un levantamiento de entre 2 y 3 metros más que el norte de Galicia desde el Último Interglacial. Es posible que Galicia norte actuara durante el Cuaternario fi nal como una zona relativamente estable entre el Golfo de Vizcaya, en el que se produce levantamiento y la costa atlántica peninsular, con claros indicios de neotectónica

A lattice field theoretical model for high-TcT_c superconductivity

We present a 2+1-dimensional lattice model for the copper oxide superconductors and their parent compounds, in which both the charge and spin degrees of freedom are treated dynamically. The spin-charge coupling parameter is associated to the doping fraction in the cuprates. The model is able to account for the various phases of the cuprates and their properties, not only at low and intermediate doping but also for (highly) over-doped compounds. We acquire a qualitative understanding of high-$T_c$ superconductivity as a Bose-Einstein condensation of bound charge pairs.Comment: talk presented in the Lattice 97 conferenc