TeV Strings and Ultrahigh-Energy Cosmic Rays

The origin and nature of ultrahigh-energy cosmic ray events, above the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy, constitute a long-standing, unsolved mistery. Neutrinos are proposed candidates but their standard interactions with matter are too weak. In the context of a TeV-scale string theory, motivated by possible extra space dimensions, the neutrino-nucleon scattering is examined. Resonant string contributions increase substantially the standard model neutrino-nucleon cross section. Although they seem insufficient to explain the trans-GZK cosmic ray events, their effects might be detected in next experiments.Comment: 12 pages, LaTeX, 2 figures; talk presented at the XXV International School of Theoretical Physics, Ustron, Poland, September 10-16, 2001. Discussion on gravity versus gauge effects improve

Resonant production of heavy MSSM Higgs bosons at the Photon Collider

Assuming a light Higgs boson is discovered, its nature may remain unknown in case that no supersymmetric particles are found. The detection and study of heavier Higgs particles is then of great interest. For this purpose the Compton-collider option of a high energy e+e- linear collider is optimal both to produce Higgs bosons and to reveal their CP-parity. Assuming realistic photon luminosities for various configurations of laser and linac polarizations, we study the heavy, neutral MSSM Higgs signals for the most relevant decay modes as well as their corresponding backgrounds. The MSSM H and A Higgs bosons with masses up to a ~80% of the linac c.m.s. energy may be observed and their CP-parity tested for Higgs masses ~450 GeV, at the gamma-gamma mode of a ~1 TeV linear collider.Comment: 1+22 pages, 8 figures; to appear in Proc. of 2nd joint ECFA/DESY Workshop on Physics Studies for a Future Linear Collider (one reference added

Eco-efficient process based on conventional machining as an alternative technology to chemical milling of aeronautical metal skin panels

El fresado químico es un proceso diseñado para la reducción de peso de pieles metálicas que, a pesar de los problemas medioambientales asociados, se utiliza en la industria aeronáutica desde los años 50. Entre sus ventajas figuran el cumplimiento de las estrictas tolerancias de diseño de piezas aeroespaciales y que pese a ser un proceso de mecanizado, no induce tensiones residuales. Sin embargo, el fresado químico es una tecnología contaminante y costosa que tiende a ser sustituida. Gracias a los avances realizados en el mecanizado, la tecnología de fresado convencional permite alcanzar las tolerancias requeridas siempre y cuando se consigan evitar las vibraciones y la flexión de la pieza, ambas relacionadas con los parámetros del proceso y con los sistemas de utillaje empleados. Esta tesis analiza las causas de la inestabilidad del corte y la deformación de las piezas a través de una revisión bibliográfica que cubre los modelos analíticos, las técnicas computacionales y las soluciones industriales en estudio actualmente. En ella, se aprecia cómo los modelos analíticos y las soluciones computacionales y de simulación se centran principalmente en la predicción off-line de vibraciones y de posibles flexiones de la pieza. Sin embargo, un enfoque más industrial ha llevado al diseño de sistemas de fijación, utillajes, amortiguadores basados en actuadores, sistemas de rigidez y controles adaptativos apoyados en simulaciones o en la selección estadística de parámetros. Además se han desarrollado distintas soluciones CAM basadas en la aplicación de gemelos virtuales. En la revisión bibliográfica se han encontrado pocos documentos relativos a pieles y suelos delgados por lo que se ha estudiado experimentalmente el efecto de los parámetros de corte en su mecanizado. Este conjunto de experimentos ha demostrado que, pese a usar un sistema que aseguraba la rigidez de la pieza, las pieles se comportaban de forma diferente a un sólido rígido en términos de fuerzas de mecanizado cuando se utilizaban velocidades de corte cercanas a la alta velocidad. También se ha verificado que todas las muestras mecanizadas entraban dentro de tolerancia en cuanto a la rugosidad de la pieza. Paralelamente, se ha comprobado que la correcta selección de parámetros de mecanizado puede reducir las fuerzas de corte y las tolerancias del proceso hasta un 20% y un 40%, respectivamente. Estos datos pueden tener aplicación industrial en la simplificación de los sistemas de amarre o en el incremento de la eficiencia del proceso. Este proceso también puede mejorarse incrementando la vida de la herramienta al utilizar fluidos de corte. Una correcta lubricación puede reducir la temperatura del proceso y las tensiones residuales inducidas a la pieza. Con este objetivo, se han desarrollado diferentes lubricantes, basados en el uso de líquidos iónicos (IL) y se han comparado con el comportamiento tribológico del par de contacto en seco y con una taladrina comercial. Los resultados obtenidos utilizando 1 wt% de los líquidos iónicos en un tribómetro tipo pin-on-disk demuestran que el IL no halogenado reduce significativamente el desgaste y la fricción entre el aluminio, material a mecanizar, y el carburo de tungsteno, material de la herramienta, eliminando casi toda la adhesión del aluminio sobre el pin, lo que puede incrementar considerablemente la vida de la herramienta.Chemical milling is a process designed to reduce the weight of metals skin panels. This process has been used since 1950s in the aerospace industry despite its environmental concern. Among its advantages, chemical milling does not induce residual stress and parts meet the required tolerances. However, this process is a pollutant and costly technology. Thanks to the last advances in conventional milling, machining processes can achieve similar quality results meanwhile vibration and part deflection are avoided. Both problems are usually related to the cutting parameters and the workholding. This thesis analyses the causes of the cutting instability and part deformation through a literature review that covers analytical models, computational techniques and industrial solutions. Analytics and computational solutions are mainly focused on chatter and deflection prediction and industrial approaches are focused on the design of workholdings, fixtures, damping actuators, stiffening devices, adaptive control systems based on simulations and the statistical parameters selection, and CAM solutions combined with the use of virtual twins applications. In this literature review, few research works about thin-plates and thin-floors is found so the effect of the cutting parameters is also studied experimentally. These experiments confirm that even using rigid workholdings, the behavior of the part is different to a rigid body at high speed machining. On the one hand, roughness values meet the required tolerances under every set of the tested parameters. On the other hand, a proper parameter selection reduces the cutting forces and process tolerances by up to 20% and 40%, respectively. This fact can be industrially used to simplify workholding and increase the machine efficiency. Another way to improve the process efficiency is to increase tool life by using cutting fluids. Their use can also decrease the temperature of the process and the induced stresses. For this purpose, different water-based lubricants containing three types of Ionic Liquids (IL) are compared to dry and commercial cutting fluid conditions by studying their tribological behavior. Pin on disk tests prove that just 1wt% of one of the halogen-free ILs significantly reduces wear and friction between both materials, aluminum and tungsten carbide. In fact, no wear scar is noticed on the ball when one of the ILs is used, which, therefore, could considerably increase tool life

Extensions in FormCalc 5.3

We present a new tool for editing Feynman diagrams as well as several extensions in version 5.3 of the package FormCalc for the calculation of Feynman diagrams.Comment: 8 pages, contribution to the proceedings of the ACAT workshop, Amsterdam, April 23-27, 200

Lepton Flavor Violation in Little Higgs Models

We report on our study of the LFV processes \mu \to e\gamma, \mu\to eee and \mu \to e conversion in the context of Little Higgs models. Specifically we examine the Littlest Higgs with T-parity (LHT) and the Simplest Little Higgs (SLH) as examples of a Product group and Simple group Little Higgs models respectively. The necessary Feynman rules for both models are obtained in the 't Hooft Feynman Gauge up to order v^2/f^2 and predictions for the branching ratios and conversion rates of the LFV processes are calculated to leading order (one-loop level). Comparison with current experimental constraints show that there is some tension and, in order to be within the limits, one requires a higher breaking scale f, alignment of the heavy and light lepton sectors or almost degenerate heavy lepton masses. These constraints are more demanding in the SLH than in the LHT case.Comment: 6 pages, 3 figures, to appear in Proceedings of the XXXIII Intl. Conf. of Theoretical Physics, "Matter to the Deepest", Ustron, Poland, September 11-16, 2009; v2: comments and references adde

Lepton Flavour Violating Z Decays in the MSSM

The possibility to observe lepton flavour violating Z decays in the GigaZ option of DESY's TESLA project consistently with present bounds from other processes is analyzed in the context of the minimal supersymmetric standard model. In particular, constraints on the slepton mass matrices from radiative lepton decays are updated and taken into account. Their correlation to the present measurement of the muon anomalous dipole moment is briefly discussed.Comment: 5 pages, 3 figures. Talk presented at the 6th International Symposium on Radiative Corrections RADCOR 2002, and the 6th Zeuthen Workshop on Elementary Particle Theory, Loops and Legs in Quantum Field Theory, Kloster Banz, Germany, 8-13 September, 2002. To appear in the proceeding

Probing TeV gravity at neutrino telescopes

Models with extra dimensions and the fundamental scale at the TeV could imply sign als in large neutrino telescopes due to gravitational scattering of cosmogenic neu trinos in the detection volume. Apart from the production of microscopic black hol es, extensively studied in the literature, we present gravity-mediated interactions at larger distances, that can be calculated in the e ikonal approximation. In these elastic processes the neutrino loses a small fracti on of energy to a hadronic shower and keeps going. The event rate of these events is higher than that of black hole formation and the signal is distinct: no charged leptons and possibly multiple-bang events.Comment: 5 pages; to appear in the proceedings of the Workshop on Exotic Physics with Neutrino Telesocpes, Uppsala 20-22 September 200

Excursions into FeynArts and FormCalc

Programming techniques which extend the capabilities of FeynArts and FormCalc are introduced and explained using examples from real applications.Comment: 5 pages, proceedings contribution to Loops and Legs 2006, Eisenach, German