Gravity-Wave Watching

It is suggested that gravity waves could, in several cases, be detected by means of already (or shortly to be) available technology, independently of current efforts of detection. The present is a follow-up on a recently suggested detection strategy based on gravity-wave-induced deviations of null geodesics. The new development is that a way was found to probe the waves close to the source, where they are several orders of magnitude larger than on the Earth. The effect translates into apparent shifts in stellar angular positions that could be as high as $10^{-7}$ arcsec, which is just about the present theoretical limit of detectability. (Calculation improved; results unchanged.)Comment: 17pp, plain LaTeX, UBCTP-93-00

Direct Detection of Gravity Waves through High-Precision Astrometry

It is generally accepted that a first ever direct detection of gravity waves would herald a new era in astronomy and in fundamental physics. Ever since the early sixties, increasingly larger human and material resources are being invested in the detection effort. Unfortunately, the gravity wave effects one has had to exploit so far are extraordinarily small and are usually very many orders of magnitude smaller than the noise involved. The detectors that are presently at the most advanced stage of development hope to register extremely rare, instantaneous longitudinal shifts that are expected to be orders of magnitude smaller than one Fermi. However, it was recently shown that gravity waves can manifest themselves through much larger effects than previously envisaged. One of these new effects is the periodic, apparent shift in a star's angular position due to a foreground gravity wave source. The comparative largeness of this effect stems from its being proportional not to the inverse of the gravity wave source's distance to the Earth, but to the inverse of its distance to the star's line of sight. In certain optimal but not unrealistic cases, the amplitude of this effect can reach the critical bar of one micro-arcsecond, thus raising the prospect that the long awaited first direct detection of gravity waves could be achieved by a high precision astrometry space mission such as GAIA.Comment: 11 pages, latex, no figure

Exact calculation of current correlations and admittance in the fractional quantum Hall regime

In this work, we focus on the finite frequency current-current correlations between edge states in a fractional quantum Hall two dimensional gas and on their relations to the quantum admittance. Using a refermionization method, we calculate these quantities within the same framework. Our results apply whatever the values of backscattering amplitude, frequency, voltage and temperature, allowing us to reach different regimes. Auto-correlations and cross-correlations exhibit distinct frequency dependencies that we discuss in detail.Comment: 4 pages, 7 figure

Finite-frequency noise in a non-interacting quantum dot

We calculate the non-symmetrized finite-frequency NS-FF noise for a single-level quantum dot connected to reservoirs in the spinless non-interacting case. The calculations are performed within the framework of the Keldysh Green's function formalism in the wide band approximation limit. We establish the general formula for NS-FF noise for any values of temperature, frequency and bias voltage. The electron transfer processes from one to the other reservoir act via the transmission amplitude and transmission coefficient depending on the energy. By taking the symmetrized version of this expression, we show that our result coincides with the expression of the finite frequency noise obtained by B\"uttiker using the scattering theory. We also give the explicit analytical expression for the NS-FF noise in the zero temperature limit. By performing numerical calculations, we finally discuss the evolution of the NS-FF noise spectrum when varying temperature, dot energy level, and coupling strength to the reservoirs, revealing a large variety of behaviors with different symmetry properties.Comment: Proceeding of the UPON 2015 conferenc

Transverse momentum correlations of quarks in recursive jet models

In the symmetric string fragmentation recipe adopted by PYTHIA for jet simulations, the transverse momenta of successive quarks are uncorrelated. This is a simplification but has no theoretical reason. Transverse momentum correlations are naturally expected, for instance, in a covariant multiperipheral model of quark hadronization. We propose a simple recipe of string fragmentation which lead to such correlations. The definition of the jet axis and its relation with the primordial transverse momentum of the quark is also discussed.Comment: 7 pages, 3 figures, 1 tabl

Two Algorithms for Network Size Estimation for Master/Slave Ad Hoc Networks

This paper proposes an adaptation of two network size estimation methods: random tour and gossip-based aggregation to suit master/slave mobile ad hoc networks. We show that it is feasible to accurately estimate the size of ad hoc networks when topology changes due to mobility using both methods. The algorithms were modified to account for the specific constraints of master/slave ad hoc networks and the results show that the proposed modifications perform better on these networks than the original protocols. Each of the two algorithms presents strengths and weaknesses and these are outlined in this paper.Comment: 3 pages, 2 figures, submitted to ANTS'09 - Corrected typos and definition