Search results for "quantum field"
showing 10 items of 492 documents
Accurate Determination of the Neutron Skin Thickness of Pb208 through Parity-Violation in Electron Scattering
2021
We report a precision measurement of the parity-violating asymmetry A_{PV} in the elastic scattering of longitudinally polarized electrons from ^{208}Pb. We measure A_{PV}=550±16(stat)±8(syst) parts per billion, leading to an extraction of the neutral weak form factor F_{W}(Q^{2}=0.00616 GeV^{2})=0.368±0.013. Combined with our previous measurement, the extracted neutron skin thickness is R_{n}-R_{p}=0.283±0.071 fm. The result also yields the first significant direct measurement of the interior weak density of ^{208}Pb: ρ_{W}^{0}=-0.0796±0.0036(exp)±0.0013(theo) fm^{-3} leading to the interior baryon density ρ_{b}^{0}=0.1480±0.0036(exp)±0.0013(theo) fm^{-3}. The measurement accurately co…
Resonance Dipole-Dipole Interaction Between Two Accelerated Atoms in the Presence of a Reflecting Plane Boundary
2018
We study the resonant dipole-dipole interaction energy between two uniformly accelerated identical atoms, one excited and the other in the ground state, prepared in a correlated {\em Bell-type} state, and interacting with the scalar field or the electromagnetic field nearby a perfectly reflecting plate. We suppose the two atoms moving with the same uniform acceleration, parallel to the plane boundary, and that their separation is constant during the motion. We separate the contributions of vacuum fluctuations and radiation reaction field to the resonance energy shift of the two-atom system, and show that Unruh thermal fluctuations do not affect the resonance interaction, which is exclusivel…
Semiclassical geons as solitonic black hole remnants
2013
We find that the end state of black hole evaporation could be represented by non-singular and without event horizon stable solitonic remnants with masses of the order the Planck scale and up to similar to 16 units of charge. Though these objects are locally indistinguishable from spherically symmetric, massive electric (or magnetic) charges, they turn out to be sourceless geons containing a wormhole generated by the electromagnetic field. Our results are obtained by interpreting semiclassical corrections to Einstein's theory in the first-order (Palatini) formalism, which yields second-order equations and avoids the instabilities of the usual (metric) formulation of quadratic gravity. We als…
Structure of the electromagnetic field around the free electron in nonrelativistic QED.
1991
We study, within the framework of nonrelativistic QED, the structure of the electromagnetic field in the neighborhood of a free spinless electron dressed by the interaction with the vacuum field. We introduce a suitable formalism that correlates electron position and field operators. The quantum average value obtained by applying correlated field operator to the dressed state gives the average value of the corresponding field quantity as a function of distance from the electron. The results obtained separately for the electric- and magnetic-field energy density around the particle display contributions that have quantum origin and that cancel in summing of the two, yielding the total energy…
Nonthermal effects of acceleration in the resonance interaction between two uniformly accelerated atoms
2016
We study the resonance interaction between two uniformly accelerated identical atoms, one excited and the other in the ground state, prepared in a correlated (symmetric or antisymmetric) state and interacting with the scalar field or the electromagnetic field in the vacuum state. In this case (resonance interaction), the interatomic interaction is a second-order effect in the atom-field coupling. We separate the contributions of vacuum fluctuations and radiation reaction to the resonance energy shift of the system, and show that only radiation reaction contributes, while Unruh thermal fluctuations do not affect the resonance interaction. We also find that beyond a characteristic length scal…
Berry's phase in Cavity QED: proposal for observing an effect of field quantization
2002
Geometric phases are well known in classical electromagnetism and quantum mechanics since the early works of Pantcharatnam and Berry. Their origin relies on the geometric nature of state spaces and has been studied in many different systems such as spins, polarized light and atomic physics. Recent works have explored their application in interferometry and quantum computation. Earlier works suggest how to observe these phases in single quantum systems adiabatically driven by external classical devices or sources, where, by classical, we mean any system whose state does not change considerably during the interaction time: an intense magnetic field interacting with a spin 1/2, or a birefringe…
Design of Wideband MIMO Car-to-Car Channel Models Based on the Geometrical Street Scattering Model
2012
Published version of an article in the journal: Modelling and Simulation in Engineering. Also available from the publisher at: http://dx.doi.org/10.1155/2012/264213 Open access We propose a wideband multiple-input multiple-output (MIMO) car-to-car (C2C) channel model based on the geometrical street scattering model. Starting from the geometrical model, a MIMO reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. The proposed channel model assumes an infinite number of scatterers, which are uniformly distributed in two rectangular areas located on both sides of the street. Analytical solutions a…
On the Problems of Symbol-Spaced Tapped-Delay-Line Models for WSSUS Channels
2007
Article from the journal: Wireless Communications and Mobile Computing The deposited fulltext is a preprint of the definitive article at Wiley Interscience http://dx.doi.org/10.1002/wcm.683 This paper analyzes the validity and statistical behavior of symbol-spaced tapped-delay-line (SSTDL) models for wide-sense stationary uncorrelated scattering (WSSUS) mobile radio channels. SSTDL models are obtained by sampling the channel impulse response (CIR) in delay domain at a rate equal to the reciprocal of the symbol duration. They were proposed more than four decades ago as canonical channel models for band-limited timevariant linear (TVL) systems, and are nowadays widely in use for assessing the…
The design of measurement-based underwater acoustic channel simulators using the INLSA algorithm
2015
This paper utilizes the iterative nonlinear least square approximation (INLSA) algorithm for designing measurement-based wideband shallow underwater acoustic (UWA) channel simulators. Measurement-based channel simulators are essential for the test, optimization, and performance analysis of UWA communication systems. The aim is to fit the time-variant channel impulse response (TVCIR) of the simulation model to that of the measured UWA channel. The performance of the designed UWA channel simulator is assessed by comparing the time-frequency correlation function (TFCF), the power delay profile (PDP), and the probability density function (PDF) of the channel envelope with the corresponding quan…
Large-photon-number limit and the essential singularity in finite quantum electrodynamics
1976
It is shown that the essential singularity in finite quantum electrodynamics can be located by considering only those diagrams with a large number of photons exchanged in the single-fermion loop, without photons emitted and absorbed on a fermion line. (AIP)