Coherent Scalar Field Research Articles

Harvesting quantum coherence from axion dark matter

Quantum coherence is one of the most striking features of quantum mechanics rooted in the superposition principle. Recently, it has been demonstrated that it is possible to harvest the quantum coherence from a coherent scalar field. In order to explore a new method of detecting axion dark matter, we consider a point-like Unruh–DeWitt detector coupled to the axion field and quantify a coherent measure of the detector. We show that the detector can harvest the quantum coherence from the axion dark matter. To be more precise, we consider a two-level electron system in an atom as the detector. In this case, we obtain the coherence measure [Formula: see text] where [Formula: see text] and [Formula: see text] are an observation time and the Lorentz factor. At the same time, the axion mass [Formula: see text] we can probe is determined by the energy gap of the detector.

Generation and catalysis of coherence with scalar fields

Recently it has been demonstrated that it is possible to harvest quantum resources other than entanglement from a coherent scalar field. Employing time-dependent perturbation theory, we present a complete analysis of the conditions under which a spatially extended Unruh-DeWitt detector coupled to the proper time derivative of the field can harvest coherence for any initial state of the field, as well as the energy cost that is required for each harvest. By studying harvesting under repeatable extractions it is proven that when the detector interacts with the field through a delta coupling coherence is catalytic. For a Gaussian smeared detector it is shown that harvesting from a coherent field depends on the phase of its amplitude distribution and its initial energy as well as on the mean radius of the detector and the mean interaction duration between the two. For a detector moving at a constant velocity and with a mean radius of the same order as its transition wavelength, we observe that, for relativistic speeds, coherence swelling effects are present the intensity of which depends on the dimension of the underlying Minkowski spacetime.

Direct observation of diffraction-induced far-field polarization effects in electromagnetic beams

Traditional Fraunhofer diffraction theory explains the far-field diffraction of fully coherent scalar fields; however, it does not include the partial coherence and partial polarization features, which are essential characteristics of a light field. We report, to the best of our knowledge, the first experimental demonstration of effect on the degree and state of polarization of partially coherent light fields caused by Fraunhofer diffraction. We have investigated this effect by synthesizing a near-unpolarized optical field having vectorial partial spatial coherence features and diffracting it with a circular aperture. We demonstrate that the spatial coherence can cause polarization modulations at the far-field, which can be reversed/nullified by controlling the size of the diffracting element. The conceptual clarity brought out by this experimental demonstration will be useful in polarization-sensitive applications such as imaging and tomography.

Aberrated dark-field imaging systems

We study generalized dark-field imaging systems. These are a subset of linear shift-invariant optical imaging systems, that exhibit arbitrary aberrations, and for which normally-incident plane-wave input yields zero output. We write down the theory for the forward problem of imaging coherent scalar optical fields using such arbitrarily-aberrated dark-field systems, and give numerical examples. The associated images may be viewed as a form of dark-field Gabor holography, utilizing arbitrary outgoing Green functions as generalized Huygens-type wavelets, and with the Young-type boundary wave forming the holographic reference.

Non-equilibrium [formula omitted] theory in open systems as a toy model of quantum field theory of the brain

We investigate non-equilibrium relativistic ϕ4 theory in open systems (the relevant system and the two reservoirs) as a toy model of quantum field theory of the brain, Quantum Brain Dynamics (QBD). We give time evolution equations of quantum fields, that is the Klein–Gordon (KG) equations for background coherent scalar fields and the Kadanoff–Baym (KB) equations for quantum fluctuations. Next we introduce a relativistic kinetic entropy current with the gradient expansion technique and show the H-theorem in the presence of Next-to-Leading-Order self-energy of the coupling expansion and tunneling between systems in d+1 dimensions. Finally we demonstrate numerical simulations with KG and KB equations in 1+1 dimensions. We find that the decoherence (field–particle conversion), the entropy production and the chemical equilibration occur in time evolution of the relevant system and the two reservoirs. We also demonstrate how the background coherent fields transfer between systems. The presented formalism is proposed as a mathematical representation of QBD.

Brief History of Ultra-light Scalar Dark Matter Models

This is a review on the brief history of the scalar field dark matter model also known as fuzzy dark matter, BEC dark matter, wave dark matter, or ultra-light axion. In this model ultra-light scalar dark matter particles with mass m = O(10-22)eV condense in a single Bose-Einstein condensate state and behave collectively like a classical wave. Galactic dark matter halos can be described as a self-gravitating coherent scalar field configuration called boson stars. At the scale larger than galaxies the dark matter acts like cold dark matter, while below the scale quantum pressure from the uncertainty principle suppresses the smaller structure formation so that it can resolve the small scale crisis of the conventional cold dark matter model.

オリフィス下流における物質移行係数の直接測定およびLESによる乱流スカラー輸送の解析

It is necessary to evaluate the geometry factor for predicting the flow accelerated corrosion (FAC) of carbon steel piping in a complicated flow field. Geometry factor is defined as the ratio of wall mass transfer coefficient in the piping systems such as orifice to that in a straight pipe. The mass transfer coefficient behind the orifice is computed by large eddy simulation (LES) and is also measured by electrochemical method. The experimental measurement is conducted with the pipe of the test section made of Ni, in which the whole pipe surface acts as electrode (referred as ’overall electrode condition’). The obtained results are compared with the previous experiments, in order to clarify the effect of the area of the electrode, with a point electrode embedded in an insulated pipe (referred as ‘point electrode condition’). Geometry factor obtained from the overall electrode condition is larger than that of a point electrode measurement. In order to simulate the mass transfer coefficient in pipe flow, we adopt the analogy between mass transfer and heat transfer, and calculate the unsteady temperature field using the numerical data of LES. Geometry factor predicted by heat transfer coefficient agrees well with that measured in overall electrode condition. The large scale motions with vortex structure of separated flow from the orifice influence the instantaneous scalar fields. Analyses of turbulent scalar transport and space-time correlation between wall scalar transfer and flow fields reveal that the mean wall scalar transfer is affected by not only near the wall region but also the coherent scalar fields away from the wall.

Coherence vortices in vortex-free partially coherent x-ray fields

We show that coherence vortices, namely screw-type topological defects in the phase of the cross-spectral density associated with a partially coherent scalar electromagnetic field, can be obtained for paraxial fields even in the absence of both scatterers and spatial vortices. The results are especially interesting at x-ray wavelengths, for which the paraxial (small-angle) approximation is usually met. A formal analogy is drawn between the cross-spectral density of a translation-invariant partially coherent system and a focused coherent wave field. This correspondence leads to a natural explanation of the coherence vortices as analogous to physical vortices that may appear around the focus of aberrated lenses. In addition, the Gouy phase shift, typical of any focused complex scalar wave field, is also derived for the one-dimensional cross section of cross-spectral density.

Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses

Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

Non-Gaussianity as a signature of thermal initial condition of inflation

We study non-Gaussianities in the primordial perturbations in single field inflation where there is radiation era prior to inflation. Inflation takes place when the energy density of radiation drops below the value of the potential of a coherent scalar field. We compute the thermal average of the two, three and four point correlation functions of inflaton fluctuations. The three point function is proportional to the slow roll parameters and there is an amplification in $f_{NL}$ by a factor of 65 to 90 due to the contribution of the thermal bath, and we conclude that the bispectrum is in the range of detectability with the 21-cm anisotropy measurements. The four point function on the other hand appears in this case due to the thermal averaging and the fact that thermal averaging of four-point correlation is not the same as the square of the thermal averaging of the two-point function. Due to this fact $\tau_{NL}$ is not proportional to the slow-roll parameters and can be as large as -42. The non-Gaussianities in the four point correlation of the order 10 can also be detected by 21-cm background observations. We conclude that a signature of thermal inflatons is a large trispectrum non-Gaussianity compared to the bispectrum non-Gaussianity.

Is Dark Matter a BEC or Scalar Field?

This is a brief review on the history of the Bose-Einstein condensate (BEC) or boson star model of galactic dark matter halos, where ultra-light scalar dark matter particles condense in a single BEC quantum state. The halos can be described as a self-gravitating, possibly self-interacting, coherent scalar field. On a scale larger than galaxies, dark matter behaves like cold dark matter while below that scale the quantum mechanical nature suppresses the dark matter structure formation due to the minimum length scale determined by the mass $m\st{>}{\sim}10^{-24} eV$ and the self-interaction of the particles. This property could alleviate the cusp problem and missing satellite problems of the $\Lambda$CDM model. Furthermore, this model well reproduces the observed rotation curves of spiral and dwarf galaxies, which makes the model promising.

Noninterferometric characterization of partially coherent scalar wave fields and application to scattered light

We report on the application of a simple propagation-based phase-space tomographic technique to the determination of characteristic projections through the mutual optical intensity and the generalized radiance of a scalar, quasi-monochromatic partially coherent wave field. This method is applied to the reconstruction of the coherence functions of an initially spatially coherent optical wave field that has propagated through a suspension of polystyrene microspheres. As anticipated, we see that the field separates into a ballistic, or unscattered, component and a scattered component with a much shorter coherence length. Good agreement is obtained between experimental results and the results of a model based on a wave-transport equation.

Scalar field oscillations contributing to dark energy

We use action-angle variables to describe the basic physics of coherent scalar field oscillations in the expanding universe. These analytical mechanics methods have some advantages, like the identification of adiabatic invariants. As an application, we show some instances of potentials leading to equations of state with $p<\ensuremath{-}\ensuremath{\rho}/3$, thus contributing to the dark energy that causes the observed acceleration of the universe.

Fate of oscillating scalar fields in a thermal bath and their cosmological implications

Relaxation process of a coherent scalar field oscillation in the thermal bath is investigated using nonequilibrium quantum field theory. The Langevin-type equation of motion is obtained which has a memory term and both additive and multiplicative noise terms. The dissipation rate of the oscillating scalar field is calculated for various interactions such as Yukawa coupling, three-body scalar interaction, and biquadratic interaction. When the background temperature is larger than the oscillation frequency, the dissipation rate arising from the interactions with fermions is suppressed due to the Pauli-blocking, while it is enhanced for interactions with bosons due to the induced effect. In both cases, we find that the microphysical detailed-balance relation drives the oscillating field to a thermal equilibrium state. That is, for low-momentum modes, the classical fluctuation-dissipation theorem holds and they relax to a state the equipartition law is satisfied, while higher-momentum modes reach the state the number density of each quanta consists of the thermal boson distribution function and zero-point vacuum contribution. The temperature-dependent dissipation rates obtained here are applied to the late reheating phase of inflationary universe. It is found that in some cases the reheat temperature may take a somewhat different value from the conventional estimates, and in an extreme case the inflaton can dissipate its energy without linear interactions that leads to its decay. Furthermore the evaporation rate of the Affleck-Dine field at the onset of its oscillation is calculated.

Roles of a coherent scalar field on the evolution of cosmic structures

A coherently oscillating scalar field, an axion as an example, is known to behave as a cold dark matter. The arguments were usually made in the Newtonian context. Ratra proved the case in relativistic context using the synchronous gauge. In this Letter we present another proof based on a more suitable gauge condition, the uniform-curvature gauge, which fits the problem. By a proper time averaging the perturbed oscillating scalar field behaves as a cold dark matter on the relevant scales including the superhorizon scale.

Grand-Unified-Theory Baryogenesis after Preheating.

At the end of inflation the universe is frozen in a near zero-entropy state with energy density in a coherent scalar field and must be ``defrosted'' to produce the observed entropy and baryon number. We propose that the baryon asymmetry is generated by the decay of supermassive Grand Unified Theory (GUT) bosons produced non-thermally in a preheating phase after inflation. We show that baryogenesis is possible for an inflaton masses of order 10^{13} GeV and a GUT Higgs boson mass of order 10^{14} GeV, thus solving many drawbacks facing GUT baryogenesis in the old reheating scenario.

Gravitational lenses and unconventional gravity theories

We study gravitational lensing by clusters of galaxies in the context of the generic class of unconventional gravity theories of the scalar--tensor type. For positive energy scalar fields with any dynamics, the bending of light by a weakly gravitating system (galaxy or cluster) is always smaller than the bending predicted by general relativity for the mass of visible and hitherto undetected matter (but excluding the scalar field energy). The same conclusion obtains within general relativity if a nonnegligible part of the mass in clusters is in coherent scalar fields, {\it i.e.\/} Higgs fields. Thus the observational claim that clusters of galaxies deflect light much more strongly than would be expected from the observable matter contained by them, cannot be interpreted in terms of some scalar-tensor unconventional gravity theory with no dark matter. If the observations eventually show that the matter distribution inferred via general relativity from the lensing is very much like that determined from the dynamics of test objects, then scalar--tensor unconventional gravity will be irrelevant for understanding the mass discrepancy in clusters. However, even a single system in which the dynamically determined mass significantly exceeds the lensing mass suggested by general relativity, would be very problematic for the dark matter picture, but would be entirely consistent with unconventional scalar--tensor gravity.

Relativistie Cosmology With Quantum Corrections

Homogeneous isotropic, anisotropic, and inhomogeneous cosmological models are studied using Einstein's general relativity with quntum corrections in field theoretical approximation. In particular we discuss coherent scalar fields and curvature squared terms in the gravitational Lagrangian. The conformal equivalence of the field equations of fourth order to general relativity with a scalar field as source is an example of the geometrization of a matter field. The aemiclassical quantum eorrections of the scalar fields can avoid the initial cosmological singularity and they lead to an inflationary evolution stage as transient attrator. The review provides new points of view on questions like the probability of the inflationary stage and the question of mechanisms for multiple inflation.

Stability of cosmological scalar fields

The Jeans instability criterium is generalized to a coherent scalar field using a quantum approach. A critical analysis of previous works about this matter is performed. The cosmological evolution of the Jeans mass during the dustlike and radiationlike matter-dominated phases of a Friedman universe is obtained. A gauge-invariant approach is used to apply our results to inflationary models.

Cosmological models with coherent scalar field oscillations in fourth-order gravity

Spatially flat Friedman models driven at early times by a coherent scalar field and the vacuum polarisation are considered. Maxima and minima as well as inflationary expansion of the scale factor result from both effects. The possibility of a start of the cosmological expansion at a finite bounce is a welcome property, but in the flat model it leads to an unstable late-time behaviour.