11 research outputs found
On Four-Point Functions of Half-BPS Operators in General Dimensions
We study four-point correlation functions of half-BPS operators of arbitrary
weight for all dimensions d=3,4,5,6 where superconformal theories exist. Using
harmonic superspace techniques, we derive the superconformal Ward identities
for these correlators and present them in a universal form. We then solve these
identities, employing Jack polynomial expansions. We show that the general
solution is parameterized by a set of arbitrary two-variable functions, with
the exception of the case d=4, where in addition functions of a single variable
appear. We also discuss the operator product expansion using recent results on
conformal partial wave amplitudes in arbitrary dimension.Comment: The discussion of the case d=6 expanded; references added/correcte
Wireless propagation modeling by using ray-tracing
The asymptotic high frequency techniques, based on the Geometrical Optics (GO), the Geometrical Theory of Diffraction (GTD), and its extension such as the Uniform Theory of Diffraction (UTD), can be used to study the propagation of wireless electromagnetic signals in complex environments. Indeed, at high frequencies, it is possible to use the ray concept to trace the paths followed by electromagnetic waves from the transmitting to the receiving antenna, and to calculate the attenuation suffered by virtue of its interaction with the obstacles present in its environment. After a brief overview of the evaluation of electromagnetic fields by using the GO and/or the GTD/UTD, the fundamental geometric concepts of the ray-tracing algorithms are presented. Next, some acceleration techniques, necessary to efficiently model wireless propagation in outdoor and indoor environments, are discussed. Furthermore, leveraging the fact that the ray-tracing algorithm provides all the data necessary for a complete characterization of wireless propagation, it is used to derive some important parameters such as Path Loss, Delay Spread, channel frequency and impulse response, Power Delay Profile and Spreading Function