Influence of Impact Parameter Fluctuations on Transverse Momentum Fluctuations

The preliminary NA49 results on the energy dependence of transverse momentum fluctuations over the whole SPS energy range exhibit an unexpected effect. The $\Phi_{p_{T}}$ fluctuation measure - used by the NA49 experiment - manifests a different behavior for different charge combinations. Whereas the $\Phi_{p_{T}}$ is consistent with zero and independent of energy for negatively charged particles, it significantly increases for both all charged and positively charged particles at lower SPS energies. The string-hadronic model UrQMD is applied here to explain this effect. The UrQMD simulations show that the number of protons is strongly correlated with impact parameter and that the event-by-event impact parameter fluctuations are responsible for the event-by-event transverse momentum fluctuations of positively charged and all charged particles where protons are included. The observations presented in this article are important for all experiments measuring event-by-event fluctuations, especially for those using all charged particles in the analysis. The results can be also crucial for detectors with acceptances extending to the beam/target spectator domains.Comment: Errata: Section 4, the end of the first paragraph - sentence in brackets modifie

Quantum Fractal Fluctuations

We numerically analyse quantum survival probability fluctuations in an open, classically chaotic system. In a quasi-classical regime, and in the presence of classical mixed phase space, such fluctuations are believed to exhibit a fractal pattern, on the grounds of semiclassical arguments. In contrast, we work in a classical regime of complete chaoticity, and in a deep quantum regime of strong localization. We provide evidence that fluctuations are still fractal, due to the slow, purely quantum algebraic decay in time produced by dynamical localization. Such findings considerably enlarge the scope of the existing theory.Comment: revtex, 4 pages, 5 figure

Stochastic Spacetime and Brownian Motion of Test Particles

The operational meaning of spacetime fluctuations is discussed. Classical spacetime geometry can be viewed as encoding the relations between the motions of test particles in the geometry. By analogy, quantum fluctuations of spacetime geometry can be interpreted in terms of the fluctuations of these motions. Thus one can give meaning to spacetime fluctuations in terms of observables which describe the Brownian motion of test particles. We will first discuss some electromagnetic analogies, where quantum fluctuations of the electromagnetic field induce Brownian motion of test particles. We next discuss several explicit examples of Brownian motion caused by a fluctuating gravitational field. These examples include lightcone fluctuations, variations in the flight times of photons through the fluctuating geometry, and fluctuations in the expansion parameter given by a Langevin version of the Raychaudhuri equation. The fluctuations in this parameter lead to variations in the luminosity of sources. Other phenomena which can be linked to spacetime fluctuations are spectral line broadening and angular blurring of distant sources.Comment: 15 pages, 3 figures. Talk given at the 9th Peyresq workshop, June 200