1,721,022 research outputs found
Sensitivity of spherical gravitational-wave detectors to a stochastic background of nonrelativistic scalar radiation
No full textWe analyze the signal-to-noise ratio for a relic background of scalar gravitational radiation composed of massive, nonrelativistic particles, interacting with the monopole mode of two resonant spherical detectors. We find that the possible signal is enhanced with respect to the differential mode of the interferometric detectors. This enhancement is due to (a) the absence of the signal suppression, for nonrelativistic scalars, with respect to a background of massless particles, and (b) for flat enough spectra, a growth of the signal with the observation time faster than for a massless stochastic background
A class of non-singular gravi-dilaton backgrounds
Full text linkWe present a class of static, spherically symmetric, non-singular solutions of the tree-level string effective action, truncated to first order in 0r\to \infty\alpha'\alpha'r\to 0r\to \infty\alpha'$ corrections, typical of string theory, in avoiding space-time singularities
Simulation of a non-invasive charge detector for quantum cellular automata
No full textInformation in a quantum cellular automata architecture is encoded in the polarization state of a cell, i.e. in the occupation numbers of the quantum dots of which the cell is made up. Non-invasive charge detectors of single electrons in a quantum dot are therefore needed, and recent experiments have shown that a quantum constriction electrostatically coupled to the quantum dot may be a viable solution. We have performed a numerical simulation of a system made of a quantum dot and a nearby quantum point contact defined, by means of depleting metal gates, in a two-dimensional electron gas at a GaAs/AlGaAs heterointerface. We have computed the occupancy of each dot and the resistance of the quantum wire as a function of the voltage applied to the plunger gate, and have derived design criteria for achieving optimal sensitivity. (C) 1998 Elsevier Science S.A. All rights reserved
TOWARDS THE INTEGRATION OF MAGNETOTELLURIC WITH GEOLOGICAL SEISMIC AND GRAVITY DATA WITHIN THE SIRIPRO PROJECT
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Nonlocal dilaton coupling to dark matter: Cosmic acceleration and pressure backreaction
No full textA model of nonlocal dilaton interactions, motivated by string duality symmetries, is applied to a scenario of "coupled quintessence" in which the dilaton dark energy is nonlocally coupled to the dark-matter sources. It is shown that the nonlocal effects tend to generate a backreaction which-for strong enough coupling-can automatically compensate the acceleration due to the negative pressure of the dilaton potential, thus asymptotically restoring the standard (dust-dominated) decelerated regime. This result is illustrated by analytical computations and numerical examples
Early acceleration and adiabatic matter perturbations in a class of dilatonic dark-energy models
No full textWe estimate the growth of matter perturbations in a class of recently proposed dark-energy models based on the (loop-corrected) gravidilaton string effective action, and characterized by a global attractor epoch in which dark-matter and dark-energy density scale with the same effective equation of state. Unlike most dark-energy models, we find that the accelerated phase might start even at redshifts as high as zapproximate to5 (thus relaxing the coincidence problem), while still producing at present an acceptable level of matter fluctuations. We also show that such an early acceleration is not in conflict with the recently discovered supernova SN 1997ff at zapproximate to1.7. The comparison of the predicted value of sigma(8) with the observational data provides interesting constraints on the fundamental parameters of the given model of dilaton-dark matter interactions
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