Causal approach for the electron-positron scattering in Generalized Quantum Electrodynamics

In this paper we study the generalized electrodynamics contribution for the electron-positron scattering process, $e^{-}e^{+}\rightarrow e^{-}e^{+}$, the Bhabha scattering. Within the framework of the standard model, for energies larger when compared to the electron mass, we calculate the cross section expression for the scattering process. This quantity is usually calculated in the framework of the Maxwell electrodynamics and, by phenomenological reasons, corrected by a cut-off parameter. On the other hand, by considering the generalized electrodynamics instead of Maxwell's, we can show that the effects played by the Podolsky mass is actually a natural cut-off parameter for this scattering process. Furthermore, by means of experimental data of Bhabha scattering we will estimate its lower bound value. Nevertheless, in order to have a mathematically well defined description of our study we shall present our discussion in the framework of the Epstein-Glaser causal theory.Comment: 24 pages, V2 to match published versio

The Epstein-Glaser causal approach to the Light-Front QED4_{4}. I: Free theory

In this work we present the study of light-front field theories in the realm of axiomatic theory. It is known that when one uses the light-cone gauge pathological poles $(k^{+}) ^{-n}$ arises, demanding a prescription to be employed in order to tame these ill-defined poles and to have correct Feynman integrals due to the lack of Wick rotation in such theories. In order to shed a new light on this long standing problem we present here a discussion based on the use rigorous mathematical machinery of distributions combined with physical concepts, such as causality, to show how to deal with these singular propagators in a general fashion without making use of any prescription. The first step of our development will consist in showing how analytic representation for propagators arises by requiring general physical properties in the framework of Wightman's formalism. From that we shall determine the equal-time (anti)commutation relations in the light-front form for the scalar, fermionic fields and for the dynamical components of the electromagnetic field. In conclusion, we introduce the Epstein-Glaser causal method in order to have a mathematical rigorous treatment of the free propagators of the theory, allowing us to discuss the general treatment for propagators of the type $(k^{+}) ^{-n}$. Moreover, we show that at given conditions our results reproduce known prescriptions in the literature.Comment: 34 pages, v2 matching the published versio

Two-fluid temperature-dependent relativistic waves in magnetized streaming pair plasmas

A relativistic two-fluid temperature-dependent approach for a streaming magnetized pair plasma is considered. Such a scenario corresponds to secondary plasmas created at the polar caps of pulsar magnetospheres. In the model the generalized vorticity rather than the magnetic field is frozen into the fluid. For parallel propagation four transverse modes are found. Two are electromagnetic plasma modes which at high temperature become light waves. The remaining two are Alfveacutenic modes split into a fast and slow mode. The slow mode is cyclotron two-stream unstable at large wavelengths and is always subluminous. We find that the instability cannot be suppressed by temperature effects in the limit of large (finite) magnetic field. The fast Alfveacuten mode can be superluminous only at large wavelengths, however it is always subluminous at high temperatures. In this incompressible approximation only the ordinary mode is present for perpendicular propagation. For oblique propagation the dispersion relation is studied for finite and large strong magnetic fields and the results are qualitatively described.Institute for Fusion Studie

Informational completeness of continuous-variable measurements

We justify that homodyne tomography turns out to be informationally complete when the number of independent quadrature measurements is equal to the dimension of the density matrix in the Fock representation. Using this as our thread, we examine the completeness of other schemes, when continuous-variable observations are truncated to discrete finite-dimensional subspaces.Comment: To appear in Phys. Rev.

Parental Education Sets the Expectation

First-generation students are worse than their non-first generation peers in their ability to recognize and respond to faculty members’ expectations (Collier & Morgan, 2008). Further, first-generation students have a lower sense of self-efficacy (Hellman, 1996) and lower self esteem(McGregor, Mayleben, Buzzanga, Davis, & Becker, 1991) than other students. I expected first generation students to more inaccurately predict how they will perform on their first introduction to psychology exam compared to their non-first generation student peers. I also expected first generation students to place a higher value of importance on their exam and experience higher levels of depression than their non-first generation student peers after the exam. We use a framework that investigates the relationship between parent’s educational attainment and college student’s educational expectations. We further this investigation by exploring how first generation status influences exam importance prior to a midterm and levels of depression experienced after the midterm. College students (N = 1435) reported their expectations and reactions before and shortly after, their midterm exam in an introductory course. They reported their expectations about how they would perform on the exam, the importance of the exam, and their depression. We examined how first generation status influenced each of these three variables. We expected first generation students to report more inaccurate expectations on exam performance, higher levels of exam importance, and higher levels of depression. Our hypothesis attempted to bridge the limited research on first generation expectations to the literature on first generation student’s well-being. First generation students and their non-first generation peers differed in their expectations and actual exam performance. First generation students reported lower expectations and performed worse than their non-first generation peers. Whether or not students were the first in their family to attend college did not affect the accuracy of their expectations for their midterm grade. First generation students and their non-first generation peers were similarly inaccurate in predicting their exam performance. Students who were first generation did differ from other students in the importance placed on the exam, and they experienced higher levels of depression after the exam