Derivation of a Vacuum Refractive Index in a Stringy Space-Time Foam Model

It has been suggested that energetic photons propagating in vacuo should experience a non-trivial refractive index due to the foamy structure of space-time induced by quantum-gravitational fluctuations. The sensitivity of recent astrophysical observations, particularly of AGN Mk501 by the MAGIC Collaboration, approaches the Planck scale for a refractive index depending linearly on the photon energy. We present here a new derivation of this quantum-gravitational vacuum refraction index, based on a stringy analogue of the interaction of a photon with internal degrees of freedom in a conventional medium. We model the space-time foam as a gas of D-particles in the bulk space-time of a higher-dimensional cosmology where the observable Universe is a D3-brane. The interaction of an open string representing a photon with a D-particle stretches and excites the string, which subsequently decays and re-emits the photon with a time delay that increases linearly with the photon energy and is related to stringy uncertainty principles. We relate this derivation to other descriptions of the quantum-gravitational refractive index in vacuo.Comment: 8 pages, 3 eps figure

Physics Motivations for Future CERN Accelerators

We summarize the physics motivations for future accelerators at CERN. We argue that (a) a luminosity upgrade for the LHC could provide good physics return for a relatively modest capital investment, (b) CLIC would provide excellent long-term perspectives within many speculative scenarios for physics beyond the Standard Model, (c) a Very Large Hadron Collider could provide the first opportunity to explore the energy range up to about 30 TeV, (d) a neutrino factory based on a muon storage ring would provide an exciting and complementary scientific programme and a muon collider could be an interesting later option.Comment: 14 pages, 1 figure, Prepared for the CERN Scientific Policy Committee in September 2001, and presented to the CERN Council in December 200

Measurement of the first internal mode of polystyrene in cyclohexane and toluene through dynamic light scattering

A study of the longest internal relaxation time {dollar}\tau\sb1{dollar} of 8.42 {dollar}\times{dollar} 10{dollar}\sp6{dollar} M{dollar}\sb{\rm w}{dollar} macromolecular polystyrene dissolved in both toluene and cyclohexane was done through the use of photon correlation spectroscopy from scattered laser light. The data obtained (autocorrelation functions) were then analyzed by means of a multi-exponential fitting programme (Discrete) on the Cyber 830 computer and by a non-linear least squares program (NLLSQ) on an Apple IIe computer. The exponential decay constants derived from these fits were further used to obtain a value of {dollar}\tau\sb1{dollar} in each solvent and also to find the power relation between these decay constants and q, the magnitude of the scattering wave vector. The relaxation time {dollar}\tau\sb1{dollar}, together with the q dependence of the decay constant, was then compared to the predicted results from the Rouse-Zimm bead-and-spring model of polymers as well as other models and other researchers\u27 published results. (Abstract shortened with permission of author.)

A new method to study energy-dependent arrival delays on photons from astrophysical sources

Correlations between the arrival time and the energy of photons emitted in outbursts of astrophysical objects are predicted in quantum and classical gravity scenarios and can appear as well as a result of complex acceleration mechanisms responsible for the photon emission at the source. This paper presents a robust method to study such correlations that overcomes some limitations encountered in previous analysis, and is based on a Likelihood function built from the physical picture assumed for the emission, propagation and detection of the photons. The results of the application of this method to a flare of Markarian 501 observed by the MAGIC telescope are presented. The method is also applied to a simulated dataset based on the flare of PKS 2155-304 recorded by the H.E.S.S. observatory to proof its applicability to complex photon arrival time distributions.Comment: 18 pages, 7 figure

An Experimental Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars

The plane-stress theory presented in Part I is shown to qualitatively predict the warping of plane sections observed in transient fringe patterns obtained using birefringent coatings and in dynamic photoelastic pictures obtained by other investigators. Measurements using conventional techniques are described in which wide rectangular bars were subjected to a longitudinal step-function pressure loading produced by a shock tube. Comparisons show that the gross features of the experimental records for the head of the pulse are qualitatively predicted by the theory. Both theory and experiment show that short-wavelength second mode disturbances arrive very early. Experimentally it is observed that these disturbances are accompanied by thickness mode activity which cannot be accounted for by the plane-stress theory

White Leghorn Egg Production During Traffic-Noise Stress

Two groups of white leghorn hens were subjected to 95 db (C) level of traffic noise and 65 db (C) level of ambient non-traffic noise. No statistically significant difference in egg production was detected between the two groups