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

Time dependent neutrino billiards

Quantum dynamica of a massless Dirac particle in time-dependent 1D box and circular billiard with time-dependent radius is studied. An exact analytical wave functions and eigenvalues are obtained for the case of linear time-dependence of the boundary position

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

Domain walls in a non-linear 2-sigma model with homogeneous quartic polynomial potential

[EN] In this paper the domain wall solutions of a Ginzburg-Landau non-linear 2-sigma hybrid model are exactly calculated. There exist two types of basic domain walls and two families of composite domain walls. The domain wall solutions have been identified by using a Bogomolny arrangement in a system of sphero-conical coordinates on the sphere 2. The stability of all the domain walls is also investigated

Domain walls in a non-linear S2-sigma model with homogeneous quartic polynomial potential

In this paper the domain wall solutions of a Ginzburg-Landau non-linear S2-sigma hybrid model are exactly calculated. There exist two types of basic domain walls and two families of composite domain walls. The domain wall solutions have been identified by using a Bogomolny arrangement in a system of sphero-conical coordinates on the sphere S2. The stability of all the domain walls is also investigated

Phase diagram and quasiparticles of a lattice SU(2) scalar-fermion model in 2+1 dimensions

The phase diagram at zero temperature of a lattice SU(2) scalar-fermion model in 211 dimensions is studied numerically and with mean-field methods. Special attention is devoted to the strong coupling regime. We have developed a new method to adapt the hybrid Monte Carlo algorithm to the O(3) non-linear σ model constraint. The charged excitations in the various phases are studied at the mean-field level. Bound states of two charged fermions are found in a strongly coupled paramagnetic phase. On the other hand, in the strongly coupled antiferromagnetic phase fermionic excitations around momenta (±π/2, ±π/2, ±π/2) emerge

Análisis estructural 3D de los invernaderos multitunel del sudeste de España. Elementos verticales

Este trabajo analiza la capacidad estructural de los elementos verticales que componen el pórtico resistente más limitativo de la variante de invernadero multitúnel más utilizada en el sudeste de España. Se estudia la influencia de la longitud y anchura del invernadero en la distribución de tensiones que se produce en dichos elementos. Se ha realizado un modelo tridimensional de elementos finitos con el programa ROBOT MILLENNIUM en su versión 20.1 en el que se ha representado la estructura de barras que conforma el invernadero. Se han analizado los resultados de tensiones normales máximas de 16 estructuras con geometría de túnel similar, pero de diferente anchura y longitud, de tal forma que la superficie en planta oscila entre los 600 m 2 y los 38.400 m 2 . El cálculo de las acciones existentes sobre los invernaderos se ha realizado según la norma UNE-EN 13031-1. Los resultados numéricos obtenidos han sido estudiados para determinar la influencia de las dimensiones del invernadero en la distribución de tensiones. Aunque se observan significativas reducciones en las tensiones con la adición de túneles, no se puede generalizar la influencia del aumento de las dimensiones del invernadero en los cambios tensionales del mismo. Los resultados obtenidos se consideran de gran utilidad para la optimización de las estructuras de los invernaderos multitúnel así como para garantizar la seguridad mecánica de las misma

Comportamiento de 13 modelos de cinta de riego en condiciones de invernadero con agua regenerada

El objetivo de este trabajo ha sido seleccionar modelos de cinta de riego con una mejor adaptación a las condiciones de invernadero y riego con aguas regeneradas. Se ha evaluado el comportamiento de 13 modelos comerciales de cintas de riego seleccionados de entre los más utilizados en los cultivos hortícolas al aire libre, y aquellos que, las empresas instaladoras y fabricantes consideren que, por sus características, pueden tener un buen comportamiento con este tipo de aguas. En la evaluación de campo todos los emisores han presentado valores de uniformidad elevados al comienzo de la campaña de riego. Cinco de las cintas se clasifican como excelentes y el resto como buenas. Al finalizar las 114 horas de trabajo decae sustancialmente la uniformidad. El comportamiento tras la finalización de la primera campaña de riego se puede considerar equiparable al obtenido en un estudio previo con una selección de 20 emisores en ramal convencional y este tipo de aguas. Se puede concluir que las cintas de riego localizado pueden ser una alternativa a los ramales de riego convencionales cuando se riega con aguas residuales urbanas regeneradas, siempre que se elija un material de una mínima calidad y el ratio de sustitución garantice una uniformidad alta

T=0 Phase Diagram of the Double-Exchange Model

We present the T=0 phase diagram of the double-exchange model (ferromagnetic Kondo lattice model) for all values of the carrier concentration $n$ and Hund's couplng $J$, within dynamical mean field theory. We find that depending on the values of $n$ and $J$, the ground state is either a ferromagnet, a commensurate antiferromagnet or some other incommensurate phase with intermediate wave vectors . The antiferromagnetic phase is separated by first order phase boundaries and wide regimes of phase separation. The transition from the ferromagnetic phase to an incommensurate phase is second order.Comment: 4 pages, 5 figures. The analysis now includes incommensurate phases with arbitrary wave vectors. Correspondingly, the figures have been change

Pathways to quiescence: SHARDS view on the star formation histories of massive quiescent galaxies at 1.0 < z < 1.5

et al.We present star formation histories (SFHs) for a sample of 104 massive (stellar massM> 1010 M) quiescent galaxies (MQGs) at z = 1.0-1.5 from the analysis of spectrophotometric data from the Survey for High-z Absorption Red and Dead Sources (SHARDS) and HST/WFC3 G102 and G141 surveys of the GOODS-North field, jointly with broad-band observations from ultraviolet (UV) to far-infrared (far-IR). The sample is constructed on the basis of restframe UVJ colours and specific star formation rates (sSFRs = SFR/Mass). The spectral energy distributions (SEDs) of each galaxy are compared to models assuming a delayed exponentially declining SFH. A Monte Carlo algorithm characterizes the degeneracies, which we are able to break taking advantage of the SHARDS data resolution, by measuring indices such as MgUV and D4000. The population of MQGs shows a duality in their properties. The sample is dominated (85 per cent) by galaxies with young mass-weighted ages, t 1.0, when our galaxies were 0.5-1.0 Gyr old. According to these SFHs, all the MQGs experienced a luminous infrared galaxy phase that lasts for ~500 Myr, and half of them an ultraluminous infrared galaxy phase for ~100 Myr. We find that the MQG population is almost assembled at z ~ 1, and continues evolving passively with few additions to the population.We acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2012-31277. NCL acknowledges financial support from AYA2013-46724-P. AAH and AHC acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA2012-31447, which is partly funded by the Fondo Europeo de Desarrollo Regional programme. The work of AC is supported by the STARFORM Sinergia Project funded by the Swiss National Science Foundation. SC acknowledges support from the ERC via an Advanced Grant under grant agreement no. 321323-NEOGAL. DC thanks AYA2012-32295. GB acknowledges support for this work from the National Autonomous University of México (UNAM), through grant PAPIIT IG100115.Peer Reviewe