Electromagnetic Corrections to Charged Pion Scattering at Low Energies

The electromagnetic corrections to the low energy scattering amplitude involving charged pions only are investigated at leading and next-to-leading orders in the two-flavour chiral expansion. As an application, the corresponding variation in the strong $2S-2P$ level shift is evaluated. The relative variation is of the order of 5%.Comment: LateX2e, 10 pages, 2 figure

On the holomorphic factorization for superconformal fields

For a generic value of the central charge, we prove the holomorphic factorization of partition functions for free superconformal fields which are defined on a compact Riemann surface without boundary. The partition functions are viewed as functionals of the Beltrami coefficients and their fermionic partners which variables parametrize superconformal classes of metrics.Comment: 5 pages, LATEX, MPI-Ph/92-7

High Efficiency Detection of Argon Scintillation Light of 128nm Using LAAPDs

The possibility of efficient collection and detection of vacuum ultraviolet light as emitted by argon, krypton, and xenon gas is studied. Absolute quantum efficiencies of large area avalanche photodiodes (LAAPDs) are derived at these wavelengths. VUV light of wavelengths down to the 128nm of Ar emission is shown to be detectable with silicon avalanche photodiodes at quantum efficiencies above 42%. Flexible Mylar foil overcoated with Al+MgF$_2$ is measured to have a specular reflectivity of $\sim$91% at argon emission wavelength. Low-pressure argon gas is shown to emit significant amounts of non-UV radiation. The average energy expenditure for the creation of non-UV photons in argon gas at this pressure is measured to be below 378 eV.Comment: 5 pages, 4 figures, Talk given at IEEE 2005 Nuclear Science Symposium and Medical Imaging Conference, Puerto Ric

Reanalysis of pion pion phase shifts from K -> pi pi decays

We re-investigate the impact of isospin violation for extracting the s-wave pion pion scattering phase shift difference delta_0(M_K) - delta_2(M_K) from K -> pi pi decays. Compared to our previous analysis in 2003, more precise experimental data and improved knowledge of low-energy constants are used. In addition, we employ a more robust data-driven method to obtain the phase shift difference delta_0(M_K) - delta_2(M_K) = (52.5 \pm 0.8_{exp} \pm 2.8_{theor}) degrees.Comment: 8 page

Complete One-Loop Renormalization of the Higgs-Electroweak Chiral Lagrangian

Employing background-field method and super-heat-kernel expansion, we compute the complete one-loop renormalization of the electroweak chiral Lagrangian with a light Higgs boson. Earlier results from purely scalar fluctuations are confirmed as a special case. We also recover the one-loop renormalization of the conventional Standard Model in the appropriate limit.Comment: 15 pages, no figures; v2: reference and comments added, typos fixed, matches published versio

The Late Prehistory of the Alutiiq People: Culture Change on the Kodiak Archipelago From 1200-1750 A.D.

Esta tesis se centra en un estudio experimental sobre la adquisición de las obstruyentes del chino y del español como L3 las oclusivas, las africadas y las fricativas. En este estudio, participaron dos grupos de hablantes: un grupo de nativos chinos cuya L2 es el inglés y cuya L3 es el español y un grupo de nativos españoles cuya L2 es el inglés y cuya L3 es el chino. Los dos grupos constituyen el grupo de análisis de su L3, al mismo tiempo, sirven de grupo de control de su L1. Ambos grupos de informantes participaron en una serie de experimentos, tanto de producción como de percepción. En la tarea de producción, se leyeron textos fonéticamente equilibrados para cada lengua y, en la de percepción, se llevó a cabo una tarea de identificación de los fonemas que presentaban alguna dificultad en la producción. De esta forma, se comprobó si en la adquisición de las obstruyentes el proceso de producción precedía al de percepción. Para analizar los datos de producción, se utilizaron dos métodos diferentes: la categorización de errores y el análisis acústico de los datos. Los resultados obtenidos señalan un comportamiento diferente en función del tipo de análisis, de la categoría, de la lengua y del tipo de tarea. En primer lugar, la sistematización de los errores requiere un análisis acústico para categorizar las realizaciones que produce el hablante. Algunas realizaciones producidas por el grupo de aprendices, que han sido categorizadas como correctas, muestran en un análisis acústico posterior características diferentes a las del grupo de nativos. En segundo lugar, categorías diferentes de sonidos presentan distintos resultados de adquisición; por lo tanto, no se pueden tratar de la misma forma. El chino y el español, aunque cuentan con algunos fonemas similares, no poseen exactamente las mismas características, lo que da lugar a una reflexión sobre el concepto de fonemas similares. La producción y la percepción también muestran resultados diferentes, indicando una complejidad en la relación de ambos procesos. Por último, los resultados obtenidos nos ayudan a interpretar mejor las interacciones entre los sistemas fónicos de un hablante y entender las influencias interlingüísticas que se pueden dar entre las lenguas que conoce un mismo hablante.This thesis aims at investigating the acquisition of Spanish and Mandarin Chinese by L3 learners. The sounds under investigation are the obstruents, namely, stops, affricates and fricatives. Two groups of participants were involved in the study: L1 Mandarin Chinese, L2 English, and L3 Spanish speakers; L1 Spanish, L2 English and L3 Mandarin Chinese speakers. The participants took part in a series of perception and production tasks for data elicitation in Chinese and Spanish. The production tasks involve in reading phonetically balanced passages. Based on their performance in production, perceptual tests were designed on those sounds which presented more difficulty. For data analysis, production data were categorized based on acoustic observation in the spectrogram and only those production which were categorized as authentic production were submitted for acoustic comparison. Later, perception tasks were performed on the sounds where more mistakes were observed. The results show that different tasks, languages, and sounds may have an effect on participants' performance. It also seems that categorization is not enough to evaluate the learners' production, since the sounds which were categorized as correct production show different acoustic performance from that of the native speakers. Secondly, not all sounds show the same degree of difficulty. Some sounds were produced and perceived more accurately than others. Thus, it may be more adequate to treat them separately during the investigation. Moreover, even though Mandarin and Spanish share some similar phonemes, they may differ acoustically. The relationship between production and perception seems to be complex and no unique pattern has been observed. All the findings seem to suggest that the cross-linguistic influence may be observed in these learners. It takes different directions and it can either facilitate or hinder learners' acquisition. Learners' L3 seems to be influenced by their L1 and L2. There also seems to be a regressive transfer on their L1

Matrix Elements of Electroweak Penguin Operators in the 1/Nc Expansion

It is shown that the K -> pi pi matrix elements of the four-quark operator Q_7, generated by the electroweak penguin-like diagrams of the Standard Model, can be calculated to first non-trivial order in the chiral expansion and in the 1/Nc expansion. Although the resulting B factors B_7^(1/2) and B_7^(3/2) are found to depend only logarithmically on the matching scale, mu, their actual numerical values turn out to be rather sensitive to the precise choice of mu in the GeV region. We compare our results to recent numerical evaluations from lattice-QCD and to other model estimates.Comment: 10 pages, LateX, two figures (inserted). Improved comparison with the lattice results. Results unchange