abstract

Because of long range interactions, the elementary excitations in a quark-gluon plasma have an unusual, non exponential damping.

abstract

In the 1950’s Hanbury Brown and Twiss showed that one could measure the angular sizes of astronomical radio sources and stars from correlations of signal intensities, rather than amplitudes, in independent detectors. Their subsequent correlation experiments demonstrating quantum bunching of photons in incoherent light beams were seminal in the development of quantum optics. Since that time the technique of “intensity interferometry” has become a valuable probe of high energy nuclear and particle collisions, providing information on the space-time geometry of the collision. The effect is one of the few measurements in elementary particle detection that depends on the wave mechanics of the produced particles. Here we discuss the basic physics of intensity interferometry, and its current applications in high energy nuclear physics, as well as recent applications in condensed matter and atomic physics.

abstract

I will present the Lund Model fragmentation in a somewhat different way than what is usually done. It is true that the formulas are derived from (semi-)classical probability arguments, but they can be motivated in a quantum mechanical setting and it is in particular possible to derive a transition matrix element. I will present two scenarios, one based upon Schwinger tunneling and one upon Wilson loop operators. The results will coincide and throw some light upon the sizes of the three main phenomenological parameters which occur in the Lund Model. After that I will show that in this way it is possible to obtain a model for the celebrated Bose–Einstein correlations between two bosons with small relative momenta. This model will exhibit non-trivial two- and three-particle BE correlations, influence the observed \(\rho \)-spectrum and finally be different for charged and neutral pion correlations.

abstract

The existence within galaxies of unidentified matter whose only action is gravity has been known since nearly two decades. Important information on its location has been obtained in the very last few years, thanks to deep stellar surveys, to the microlensing events detected by the EROS, MACHO and OGLE experiments that trace dark stellar-size objects as well as to the quite recent HIPPARCOS data that have determined very accurately the stellar phase-space and whence the gravitational potential in the solar neighborhood. We review these results and discuss what they imply on the nature of Dark Matter within our Galaxy.

abstract

Even for free fields, canonical quantization is problematic when the space-time is not flat. There is a problem in identifying the proper degrees of freedom of the quantum field. In particular, for open Friedmann–Robertson–Walker universes modes which are not \(L^{2}\)-normalizable may exist, and there is a controversy whether or not they contribute to the quantum fluctuations. We have shown unambiguously that these modes are allowed by quantum mechanics. Their appearance turns out to be an essential ingredient if one wants to insure invariance properties of the correlation functions in the maximal symmetric de Sitter case.