Eccentricity fluctuations are not the only source of elliptic flow fluctuations in a multiphase transport model

Sources of event-by-event elliptic flow fluctuations in relativistic heavy-ion collisions are investigated in a multiphase parton transport model(AMPT).Besides the well-known initial eccentricity fluctuations,several other sources of elliptic flow dynamical fluctuations are identified.One is fluctuations in initial parton configurations at a given eccentricity.Configuration fluctuations are found to be as important as eccentricity fluctuations in elliptic flow development.A second is quantum fluctuations in parton-parton interactions during system evolution.A third is fluctuations caused by hadronization and final-state hadronic scatterings.The magnitudes of these fluctuations are investigated relative to the eccentricity fluctuations and the average elliptic flow magnitude.The fluctuations from the latter two sources are found to be negative.The results may have important implications for the interpretation of elliptic flow data.     

Spacetime Metric and Lightcone Fluctuations

Several aspects of the quantum fluctuations ofspacetime geometry are discussed. A model for lightconefluctuations is described in which a bath of gravitonsleads to metric fluctuations. The operational definitions of such phenomena as lightcone andhorizon fluctuations are examined. The problem ofdescribing fluctuations of a quantum stress tensor isalso discussed. The possibility that one can gain some insights about spacetime geometry fluctuationsfrom studies of the force fluctuations on materialbodies is suggested.     

Stress Tensor Fluctuations and Passive Quantum Gravity

The quantum fluctuations of the stress tensor of a quantum field are discussed, as are the resulting space-time metric fluctuations. Passive quantum gravity is an approximation in which gravity is not directly quantized, but fluctuations of the space-time geometry are driven by stress tensor fluctuations. We discuss a decomposition of the stress tensor correlation function into three parts, and consider the physical implications of each part. The operational significance of metric fluctuations and the possible limits of validity of semiclassical gravity are discussed.     

Mesoscopic fluctuations of tunneling and cotunneling in quantum dots

Recent measurements of mesoscopic tunneling and cotunneling fluctuations in Coulomb blockaded ballistic quantum dots are presented. The statistics and parametric fluctuations (as a function of magnetic field) of Coulomb blockade peak heights are found to be consistent with random-matrix-theory predictions. Mesoscopic fluctuations of elastic cotunneling, measured in the valleys between blockade peaks, are also presented along with a semiclassical explanation of the observed enhancement of the magnetic field scale of cotunneling fluctuations compared to resonant tunneling fluctuations.     

On potential and field fluctuations in two-dimensional classical charged systems

We supplement a previous paper on three-dimensional systems by studying the electric potential and field fluctuations in two-dimensional Coulomb systems. The novelty in two dimensions is that the fluctuations of the potential at a point are infinite in the thermodynamic limit. However, the potential difference between two points has finite fluctuations, which resemble the ones which occur in the three-dimensional case. The field fluctuations are also rather similar in both cases. The correlations do not have a fast decay. Explicit results are obtained for a solvable model; the fluctuations of the potential are Gaussian with an infinite variance.This laboratory is associated with the Centre National de la Recherche Scientifique.     

Large-Scale Two-Dimensional Quantum Fluctuations of Five-Dimensional and Four-Dimensional Space-Time Metrics

Large-scale two-dimensional quantum fluctuations of five-dimensional space-time metric are constructed and the effect of the fluctuations on the nested four-dimensional worlds is studied. In doing so, the fluctuations affect not all four-dimensional worlds but only a part of them. The energy-momentum tensor of four-dimensional space-time has a physical form both in the absence and in the presence of fluctuations; it means that the fluctuations can be realized by real matter. A spatial region occupied by the fluctuations constructed in this work can be infinitely large and the fluctuations can occur during a long period of time. Therefore, we refer to these fluctuations as large-scale fluctuations.     

Structural fluctuations in nanoparticles

Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature stating that fluctuations are possible only between an equilibrium and a non-equilibrium phase. The basic conditions used to describe fluctuations are well suited to calculate the limits for fluctuations as function of temperature and particle size.     

Correlation properties of black-body radiation in the context of the electron cyclotron emission of a magnetized plasma

Summary The quest for the cause of the anomalously large heat transport in magnetically confined thermonuclear plasmas has motivated detailed studies of fluctuations of various plasma parameters and, among others, of the electron temperature fluctuations. For an optically thick plasma the fluctuations of the electron cyclotron emission, ECE, are proportional to the electron temperature fluctuations up to a critical frequency where this ceases to be true. For the ultimate purpose of recovering, by correlation analysis, the actual plasma temperature fluctuations from the fluctuations of the measured radiation at frequencies above the critical, the mutual correlation properties of two ECE beams are analyzed and a criterion is obtained to decide when the thermal radiation fluctuations are uncorrelated and hence ignorable. The author of this paper has agreed to not receive the proofs for correction.     

Classical Coulomb systems: Screening and correlations revisited

From the laws of macroscopic electrostatics of conductors (in particular, the existence of screening), taken as given, one can deduce universal properties for the thermal fluctuations in a classical Coulomb system at equilibrium. The universality is especially apparent in the long-range correlations of the electrical potentials and fields. The charge fluctuations are derived from the field fluctuations. This is a convenient way to study the surface charge fluctuations on a conductor with boundaries. Explicit results are given for simple geometries. The potentials and the fields have Gaussian fluctuations, except for a short-distance cutoff.laboratory associated with the Centre National de la Recherche Scientifique.     

Effect of equilibrium fluctuations on superfluid density in layered superconductors

Using a phenomenological approach based on the fluctuation-dissipation theorem we calculate suppression of superconducting currents due to phase fluctuations and find that, in contrast to a recent prediction, the effect of thermal fluctuations cannot account for linear temperature dependence of the superfluid density in high-T(c) superconductors at low temperatures. Quantum fluctuations are found to dominate over thermal fluctuations at low temperatures. Near T(c) sizable thermal fluctuations are found to suppress the critical current in the stack direction stronger than in the direction along the layers. The spectral density of voltage fluctuations at small frequencies is nonzero, in contrast to what may be expected from a naive interpretation of the Nyquist formula.     

Fluctuations in the phase-conjugate signal generated via degenerate four-wave mixing

The excess fluctuations of the phase-conjugate (PC) signal generated via pulsed degenerate four-wave mixing (DFWM) in sodium vapor are investigated. Various dye-laser oscillator and amplifier combinations are employed to trace the sources of these fluctuations. For DFWM driven by an externally-stabilized cw dye-laser oscillator amplified with a dye system pumped by the smoothed pulses of a Nd:YAG laser, the PC excess fluctuations are very highly correlated with the energy fluctuations of the input amplified dye-laser pulses. Thus, input-pulse selection on the basis of energy alone permits observation of the quantum-mechanical fluctuations of the PC signal.     

On the slow dynamics of density fluctuations near the colloidal glass transition

Slow dynamics of density fluctuations near the colloidal glass transition is discussed from a new viewpoint by numerically solving a nonlinear stochastic diffusion equation for the density fluctuations recently proposed by one of the present authors (MT). The effects of spatial heterogeneities on the dynamics of density fluctuations are then investigated in an equilibrium system. The spatial heterogeneities are generated by the nonlinear density fluctuations, while in a nonequilibrium system they are described by a nonlinear deterministic equation for the average number density. The dynamics of equilibrium density fluctuations is thus shown to be quite different from that of nonequilibrium ones, leading to a logarithmic decay followed by less distinct α- and β-relaxation processes. Received 9 March 2002 and Received in final form 19 September 2002     

Noise power fluctuations and the masking of sine signals

This article is concerned with fluctuations in noise power and with the role that such fluctuations play in the masking of sine signals by noise. Several measures of noise fluctuations are discussed: the fourth moment of the waveform, the fourth moment of the envelope, and the crest factor. Relationships among these quantities are found for cases of equal-amplitude random-phase noise and Rayleigh-distributed-amplitude noise. Of particular interest is a special non-Gaussian noise called low-noise noise in which the fluctuations are small by any of our measures. The results of frozen-noise masking experiments are reported, where the noise waveform was fixed for all stimulus presentations. In separate experiments, equal-amplitude random-phase Gaussian noise, with typical fluctuations, and low-noise noise, with almost no fluctuations were used. The data show that for a noise bandwidth less than the critical bandwidth, the masked threshold is about 5 dB lower for low-noise noise than for Gaussian noise. When the noise bandwidth is larger than the critical bandwidth, the masked threshold is the same for both kinds of noise. It is concluded that noise power fluctuations increase masked threshold by about 5 dB and that filtering by the auditory system reintroduces fluctuations into broadband low-noise noise.     

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 that can be linked to spacetime fluctuations are spectral line broadening and angular blurring of distant sources.     

Fluctuations of quantum entanglement

It is emphasized that quantum entanglement determined in terms of the von Neumann entropy operator is a stochastic quantity and, therefore, can fluctuate. The rms fluctuations of the entanglement entropy of two-qubit systems in both pure and mixed states have been obtained. It has been found that entanglement fluctuations in the maximally entangled states are absent. Regions where the entanglement fluctuations are larger than the entanglement itself (strong fluctuation regions) have been revealed. It has been found that the magnitude of the relative entanglement fluctuations is divergent at the points of the transition of systems from an entangled state to a separable state. It has been shown that entanglement fluctuations vanish in the separable states.     

无耗散介观电感耦合电路的量子效应

本文从无耗散的电感耦合电路的经典运动方程出发,分别研究了这一耦合电路在其任意的本征态下和压缩真空态下电路中电荷、电流的量子涨落,其结果表明,每个回路中的电荷、电流都存在着量子涨落,且两回路中的量子噪音是相互关联的。     

Quantum Fluctuations in a Mesoscopic Inductance Coupling Circuit

Starting from the equation of motion of a mesoscopic inductance coupling circuit,the quantum fluctuations of charge and current in the circuit are investigated inboth the eigenstates of the system and the squeezed vacuum state. The resultsshow that there exist quantum fluctuations of the charge and current in bothcases, and the fluctuations in each component circuit are connected.     

On the Physical Origin of Long-Ranged Fluctuations in Fluids in Thermal Nonequilibrium States

Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.     

Gradient-driven fluctuations in microgravity

Equilibrium fluctuations of thermodynamic variables, such as density or concentration, are known to be small and typically occur at a molecular length scale. In contrast, theory predicts that non-equilibrium fluctuations grow very large both in amplitude and spatial size. On earth, the presence of gravity and buoyancy forces severely limits the development of the fluctuations. We will present the results of a 14-year long international collaboration on an experiment on non-equilibrium fluctuations in a single liquid and in a polymer solution under microgravity conditions. Non-equilibrium conditions are generated by applying a temperature gradient across millimetre-size liquid slabs. Phase modulations introduced by fluctuations are measured using a quantitative shadowgraph method, with the optical axis parallel to the temperature gradient. Thousands of images are analysed and their two-dimensional power spectra yield the fluctuation structure function S(q), once data are reduced accounting for the instrumental transfer function T(q). The mean-squared amplitude of the fluctuations exhibits an impressive power-law dependence at larger q and a crossover at low q showing that the fluctuation size is limited by the sample thickness. The shape of the structure function, its increase due to removing gravity, and its dependence on applied gradient are in reasonable agreement with available theoretical predictions.     

Suppression of superconductivity in disordered interacting wires

We study superconductivity suppression due to thermal fluctuations in disordered wires using the replica nonlinear sigma-model (NLsigmaM). We show that in addition to the thermal phase slips there is another type of fluctuations that result in a finite resistivity. These fluctuations are described by saddle points in NLsigmaM and cannot be treated within the Ginzburg-Landau approach. The contribution of such fluctuations to the wire resistivity is evaluated with exponential accuracy. The magnetoresistance associated with this contribution is negative.