2PI effective action for gauge theories: Renormalization

We discuss the application of two-particle-irreducible (2PI) functional techniques to gauge theories, focusing on the issue of non-perturbative renormalization. In particular, we show how to renormalize the photon and fermion propagators of QED obtained from a systematic loop expansion of the 2PI effective action. At any finite order, this implies introducing new counterterms as compared to the usual ones in perturbation theory. We show that these new counterterms are consistent with the 2PI Ward identities and are systematically of higher order than the approximation order, which guarantees the convergence of the approximation scheme. Our analysis can be applied to any theory with linearly realized gauge symmetry. This is for instance the case of QCD quantized in the background field gauge.Comment: 21 pages, 8 figures. Uses JHEP3.cl

Advanced FE models of stiffened cleat angle connections

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.In this paper, the development of reliable 3D FE models of stiffened angle connections is dealt with. These advanced models will permit to obtain the assessment of the 3D deformational response of some future tests. Abaqus® finite element code was used to carry the 3D finite element analyses out. Symmetry was considered for these numerical analyses so a quarter of the geometry was modelled. The results obtained are compared with those from the analysis of the analogous specimens but without the top angle stiffener, showing an important increase in the initial connection stiffness. At the same time, the stress increment in the column panel zone due to the presence of the angle stiffener has been discussed

Ward Identities for the 2PI effective action in QED

We study the issue of symmetries and associated Ward-like identities in the context of two-particle-irreducible (2PI) functional techniques for abelian gauge theories. In the 2PI framework, the $n$-point proper vertices of the theory can be obtained in various different ways which, although equivalent in the exact theory, differ in general at finite approximation order. We derive generalized (2PI) Ward identities for these various $n$-point functions and show that such identities are exactly satisfied at any approximation order in 2PI QED. In particular, we show that 2PI-resummed vertex functions, i.e. field-derivatives of the so-called 2PI-resummed effective action, exactly satisfy standard Ward identities. We identify another set of $n$-point functions in the 2PI framework which exactly satisfy the standard Ward identities at any approximation order. These are obtained as field-derivatives of the two-point function \bcG^{-1}[\phi], which defines the extremum of the 2PI effective action. We point out that the latter is not constrained by the underlying symmetry. As a consequence, the well-known fact that the corresponding gauge-field polarization tensor is not transverse in momentum space for generic approximations does not constitute a violation of (2PI) Ward identities. More generally, our analysis demonstrates that approximation schemes based on 2PI functional techniques respect all the Ward identities associated with the underlying abelian gauge symmetry. Our results apply to arbitrary linearly realized global symmetries as well.Comment: 33 pages, 2 figure

Experiencia de asistencia remota nunha asignatura base dunha enxeñería

[Resumo] Neste traballo reflíctese unha experiencia de asistencia remota nunha asignatura base dunha enxeñería. Trátase da asignatura Resistencia dos Materiais, impartida no segundo cuatrimestre en distintos graos no ámbito da enxeñería industrial. A teoría, boletíns de exercícios e prácticas de laboratorio impartíronse en modalidade asíncrona mediante videos breves realizados con ScreenCastOMatic, usando como repositorio a páxina de Moodle da asignatura. Asociado a cada tema había un cuestionario Moodle para reforzar a teoría. Realizouse unha programación síncrona de casos prácticos con un foro de dúbidas asociado. A avaliación constaba de exame final, cuestionarios e práctica de laboratorio. Os exercicios do exame abríanse paulatinamente en Moodle e resolvíanse a man para ser posteriormente escaneados e enviados via correo electrónico. As tutorías, resolvéronse síncronamente por correo electrónico. As incidencias foron pouco significativas, debidas maioritariamente á entrega do exame fóra do prazo establecido. Os resultados, vistos coa perspectiva de anos anteriores, foron excelentes non só pola elevada taxa de éxito, senon tamén pola baixa taxa de non presentados.[Abstract] This work reflects an experience of remote assistance in a basic subject of an engineering. The subject Mechanics of Materials, taught in the second semester in different degrees in the field of industrial engineering. The theory, exercise bulletins and laboratory practices were taught in asynchronous mode using short videos made with ScreenCastOMatic, using the subject's Moodle page as a repository. Associated with each topic was a Moodle questionnaire to reinforce the theory. A synchronous scheduling of case studies was conducted with an associated question forum. Tutorials were resolved synchronously by email. The assessment consisted of final exam, questionnaires and laboratory practice. The exam exercises were gradually opened in Moodle and solved by hand to be subsequently scanned and emailed. The incidences were insignificant, mainly due to the delivery of the exam outside the established deadline. The results, seen with the perspective of previous years, were excellent not only by the high success rate, but also by the low rate of not presenting.http://hdl.handle.net/2183/2879

Uso de test interactivos en la plataforma Moodle para una asignatura base de una ingeniería

[Resumen] La plataforma Moodle cuenta con interesantes herramientas que pueden resultar útiles a la hora de motivar al alumnado e incrementar la tasa de éxito asociada a una asignatura. El presente artículo muestra la experiencia del uso de la herramienta "prueba tipo test" de Moodle en una asignatura de segundo curso de una ingeniería. Tras haberse detectado un bajo seguimiento de la asignatura durante el curso, se tomó la decisión de complementar los boletines de prácticas con test teóricos que constaban básicamente de dos tipos de cuestiones: preguntas simples con un texto sencillo asociado y varias opciones de respuesta, y cuestiones gráficas donde el alumnado debe arrastrar el gráfico correcto a la cuestión requerida. Los test eran susceptibles de repetirse, quedando reflejados en la aplicación todos los intentos y el éxito o fracaso en cada uno de ellos. En un primer término, se decidió que la participación fuese voluntaria, confiando en obtener una atención razonable e incrementar por tanto el seguimiento de la asignatura. Tras una experiencia negativa, con posterioridad, se ofrecieron los test de nuevo como una opción voluntaria, pero advirtiendo al alumnado de que una de las cuestiones sería requerida en el examen. Este cambio incrementó la participación y, por consiguiente, el seguimiento de la asignatura como se demostrará en este trabajo. De la correlación entre alumnos participantes y aprobados en el examen final, puede extrapolarse un beneficio directo de esta medida, que invita a mantenerla y tal vez complementarla

2PI Effective Action and Evolution Equations of N = 4 super Yang-Mills

We employ nPI effective action techniques to study N = 4 super Yang-Mills, and write down the 2PI effective action of the theory. We also supply the evolution equations of two-point correlators within the theory.Comment: 16 pages, 6 figures. Figure 2 replaced, approximation scheme clarified, references adde