First quantized approaches to neutrino oscillations and second quantization

Neutrino oscillations are treated from the point of view of relativistic first quantized theories and compared to second quantized treatments. Within first quantized theories, general oscillation probabilities can be found for Dirac fermions and charged spin 0 bosons. A clear modification in the oscillation formulas can be obtained and its origin is elucidated and confirmed to be inevitable from completeness and causality requirements. The left-handed nature of created and detected neutrinos can also be implemented in the first quantized Dirac theory in the presence of mixing; the probability loss due to the changing of initially left-handed neutrinos to the undetected right-handed neutrinos can be obtained in analytic form. Concerning second quantized approaches, it is shown in a calculation using virtual neutrino propagation that both neutrinos and antineutrinos may also contribute as intermediate particles. The sign of the contributing neutrino energy may have to be chosen explicitly without being automatic in the formalism. At last, a simple second quantized description of the flavor oscillation phenomenon is devised. In this description there is no interference terms between positive and negative components, but it still gives simple normalized oscillation probabilities. A new effect appearing in this context is an inevitable but tiny violation of the initial flavor of neutrinos. The probability loss due to the conversion of left-handed neutrinos to right-handed neutrinos is also presented.

Analytic properties of thermal corrected boson propagators

We investigate the analytic properties of finite-temperature self-energies of bosons interacting with fermions at one-loop order. A simple boson-fermion model was chosen due to its interesting features of having two distinct couplings of bosons with fermions. This leads to a quite different analytic behavior of the bosons self-energies as the external momentum K-mu=(k(0),k) approaches zero in the two possible limits. It is shown that the plasmon and Debye masses are consistently obtained at the pole of the corrected propagator even when the self-energy is analytic at the origin in the frequency-momentum space.

A emergência do pluralismo teórico-metodológico na alfabetização: em busca de uma prática pedagógica para formar escritores

This qualitative research was performed with the goal of investigating the contributions of theoretical and methodological perspectives in the alphabetization process, aiming to train proficient writers of texts with communicative function. Hence, such were the goals established for this research: giving a retrospective look on the synthetic and analytic methods of teaching literacy; verifying the possibilities and limits of theoretical and methodological approaches of acquiring the ability to write and identifying the teachers’ ideas concerning basic concepts (such as literacy, text and textual genres) imbued in the teaching of writing; and establishing which activities they develop in the course of teaching whether the pedagogical practices of the teacher observed contributed to the formation of students who were capable of producing significant texts of diverse genres, suitable to the objectives, to the readers, and to the context of the circulation of texts. The research was done in a public elementary school, in a 2nd grade class of the city of Jaú. Subjects of the research were four teachers and twenty-eight children. For this work, two instruments were used for data collecting: a questionnaire and direct observation, registered in research diaries. Among the observations made were that, although there are many studies on literacy, the practices actually adopted in class are empirical in nature and do not contribute to the process of developing individual writing or reading skills at all; rather, it is only valued the ability of establishing relations between phonemes and graphemes; literacy teachers do not have adequate knowledge of concepts of literacy, teaching, text and textual genres, valuing only one methodological theory and disregarding other contributions on the field of text production