bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation and propagation of localized states in extended systems
Authors: Bestehorn M. , Grigorieva E.V. 
Published: June 2022

AbstractWe study a one‐species‐diffusion equation supplemented by a nonlinear saturation term. If this term includes temporal delay, a rich spatio‐temporal behavior already at the critical point where the steady homogeneous solution gets unstable is expected. Normal form transformation into a complex Ginzburg‐Landau equation shows that the condition for phase turbulence is always fulfilled. As a secondary instability of these chaotic states well ordered spiral waves and targets are found numerically. Here the system shows features well‐known from excitable media. Finally we propose the construction of logical circuits by means of a network built up by one‐dimensional excitable media.
Asymptotic properties of nonlinear diffusion, nonlinear drift‐diffusion, and nonlinear reaction‐diffusion equations
Authors: Frank T.D. 
Published: June 2022

AbstractWe review a Fokker‐Planck approach to nonlinear evolution equations such as nonlinear diffusion equations and nonlinear drift‐diffusion equations and extend this approach to nonlinear reaction‐diffusion equations. Using this Fokker‐Planck approach along with appropriately defined entropy and free energy measures, we show that transient solutions converge to stationary ones in the long time limit. Implications for bifurcation theory are also addressed.
An impedance spectroscopy study in poly(butylene adipate) ionomers
Authors: Yakuphanoglu F. , Yoo Y.T. , Okutan M. 
Published: June 2022

AbstractPoly(butylenes adipate) ionomers (PBAi) were synthesized using dimethyl 5‐sulfoisophthalate sodium salt (DMSI) up to 5 mol% of diacid monomer. We have investigated electrical and dielectric properties of the ionomers to evaluate alternating current (AC) parameters such as impedance, conductance, dielectric constant, admittance, susceptance, dielectric loss, and resistance by an impedance spectroscopy. It is seen that the ionic conductances of the ionomers increase with increasing content of DMSI. The AC conductance for the ionomers was found to vary as ωs with the index s ≥ 1. A decrease in the relative dielectric constant of the ionomers is observed with the increase in the ionic content. The electrical relaxation in the dielectric spectra of the ionomers was not observed due to the orientation polarization of the dipoles. It is also observed that the tangent loss increases with the increase in the ionic content.
Matrix perturbation theory for driven three‐level systems with damping
Authors: Sanchez B.N. , Brandes T. 
Published: June 2022

AbstractWe investigate the dynamics of the Λ system driven by two resonant laser fields in presence of dissipation for coupling strengths where the rotating‐wave approximation starts to break down. This regime is characterised by Rabi frequencies being approximately equal or smaller than the field frequencies. A systematic procedure to obtain an expansion for the solution of the Bloch evolution equations of the system is presented. The lowest contribution results to be the well‐known rotating‐wave approximation. The method is based on a semi‐classical treatment of the problem, and its predictions are interpreted fully quantum mechanically. The theory is illustrated by a detailed study of the disappearance of coherent population trapping as the intensities of the fields increase.
QCD sum rules and models for generalized parton distributions*
Authors: Radyushkin A. 
Published: June 2022

AbstractI use QCD sum rule ideas to construct models for generalized parton distributions. To this end, the perturbative parts of QCD sum rules for the pion and nucleon electromagnetic form factors are interpreted in terms of GPDs and two models are discussed. One of them takes the double Borel transform at adjusted value of the Borel parameter as a model for nonforward parton densities, and another is based on the local duality relation. Possible ways of improving these Ansätze are briefly discussed.
Generalized parton distributions, nucleon form factors, and large‐t processes*
Authors: Vanderhaeghen M. 
Published: June 2022

AbstractThe connection of generalized parton distributions (GPDs) to processes at large momentum transfer (high‐t), and the links between GPDs and elastic nucleon form factors are discussed here. These links, in the form of sum rules, represent powerful constraints on parametrizations of GPDs. A Regge parametrization for the GPDs at small‐t, which is surprisingly observed from the chiral quark soliton model results, is extended to the large‐t region and it is found to catch the basic features of proton and neutron electromagnetic form factor data. It is furthermore discussed how these GPDs at large‐t enter into two‐photon exchange processes and resolve the discrepancy between Rosenbluth and polarization experiments of elastic electron nucleon scattering.
Derivation of Poincaré invariance from general quantum field theory
Authors: Froggatt C.D. , Nielsen H.B. 
Published: June 2022

AbstractStarting from a very general quantum field theory we seek to derive Poincaré invariance in the limit of low energy excitations. We do not, of course, assume these symmetries at the outset, but rather only a very general second quantised model. Many of the degrees of freedom on which the fields depend turn out to correspond to a higher dimension. We are not yet perfectly successful. In particular, for the derivation of translational invariance, we need to assume that some background parameters, which a priori vary in space, can be interpreted as gravitational fields in a future extension of our model. Assuming translational invariance arises in this way, we essentially obtain quantum electrodynamics in just 3+1 dimensions from our model. The only remaining flaw in the model is that the photon and the various Weyl fermions turn out to have their own separate metric tensors.
Dirac particle in a plane wave field and the semi‐classical approximation
Authors: Bourouaine S. 
Published: June 2022

AbstractIn this paper we investigate the influence of photon represented by plane wave field on Dirac particle in the context of path integral approach given by Fradkin and Gitman formalism. In our case, although the action relative to Dirac particle in plane wave field seems to be non quadratic, the result obtained by semi‐classical approach is the same as that found by an exact calculation. Hence; when we add the plane wave field to any quadratic actions related to Fradkin and Gitman approach, the total action behaves like quadratic.
Quantum phase diagram for homogeneous Bose‐Einstein condensate
Authors: Kleinert H. , Schmidt S. , Pelster A. 
Published: June 2022

AbstractWe calculate the quantum phase transition for a homogeneous Bose gas in the plane of s‐wave scattering length as and temperature T. This is done by improving a one‐loop result near the interaction‐free Bose‐Einstein critical temperature Tc(0) with the help of recent high‐loop results on the shift of the critical temperature due to a weak atomic repulsion based on variational perturbation theory. The quantum phase diagram shows a nose above Tc(0), so that we predict the existence of a reentrant transition above Tc(0), where an increasing repulsion leads to the formation of a condensate.
Quadratic metric‐affine gravity
Authors: Vassiliev D. 
Published: June 2022

AbstractWe consider spacetime to be a connected real 4‐manifold equipped with a Lorentzian metric and an affine connection. The 10 independent components of the (symmetric) metric tensor and the 64 connection coefficients are the unknowns of our theory. We introduce an action which is (purely) quadratic in curvature and study the resulting system of Euler–Lagrange equations. In the first part of the paper we look for Riemannian solutions, i.e. solutions whose connection is Levi‐Civita. We find two classes of Riemannian solutions: 1) Einstein spaces, and 2) spacetimes with pp‐wave metric of parallel Ricci curvature. We prove that for a generic quadratic action these are the only Riemannian solutions. In the second part of the paper we look for non‐Riemannian solutions. We define the notion of a “Weyl pseudoinstanton” (metric compatible spacetime whose curvature is purely of Weyl type) and prove that a Weyl pseudoinstanton is a solution of our field equations. Using the pseudoinstanton approach we construct explicitly a non‐Riemannian solution which is a wave of torsion in a spacetime with Minkowski metric. We discuss the possibility of using this non‐Riemannian solution as a mathematical model for the neutrino.
Ginzburg–Landau equations and boundary conditions for superconductors in static magnetic fields
Authors: Bünemann J. , Gebhard F. 
Published: June 2022

AbstractWe derive the Ginzburg–Landau equations for superconductors in static magnetic fields. Instead of the square of the gauge‐invariant gradient of the order‐parameter wave function, we consider the quantum‐mechanical expression for the kinetic energy in the Ginzburg–Landau energy functional. We introduce a new surface term in the free energy functional which results in the de Gennes interface conditions. The phenomenological Ginzburg–Landau theory thus contains three length scales which must be determined from microscopic theory: the Ginzburg–Landau coherence length, the London penetration depth, and the de Gennes length.
Excited 0+ states in 156,158,160,162 Gd
Authors: Gerçeklioglu M. 
Published: June 2022

AbstractExcited Kπ = 0+ states in 156,158,160,162 Gd isotopes are studied by using the pairing plus quadrupole model (PPQ). To determine the nature and the general trend of the properties of these states depending on the neutron number, B(E2), ρ2(E0) values and two‐nucleon transfer strengths are calculated. We observe that by means of the PPQ model, approximately 13‐14 0+ states can be obtained up to 3.3 MeV for the nuclei in question, where most of them are two‐quasiparticle (2qp) in character.
The variable viscoelasticity oscillator
Authors: Soon C.M. , Coimbra C.F.M. , Kobayashi M.H. 
Published: June 2022

AbstractThe complex dynamics of a variable viscoelasticity oscillator is studied using the novel concept of Variable‐Order (VO) Calculus. The damping force in the oscillator varies continuously between the elastic and viscous regimes depending on the position of the mass. The oscillator considered here is composed of a linear spring of stiffness k that inputs a restitutive force Fk = ‐k x, a VO damper of order q(x(t)) that generates a damping force Fq = ‐cq 𝒟q(x(t)) x, and a mass m. A modified Runge‐Kutta method is used in conjunction with a trapezoidal numerical integration technique to yield a second‐order accurate method for the solution of the resulting VO Differential Equation (VODE). The VO oscillator is also modelled using a Constant Order (CO) formulation where a number of CO fractional order differentials are weighted to simulate the VO behavior. The CO formulation asymptotically approaches the VO results when a relatively large number of weights is used. For the viscoelastic range of 0 ≤ q ≤ 1, the dynamics of the oscillator is well approximated by the CO formulation when 5 or more fractional terms are included (e.g., 0, 1/4, 1/2, 3/4, and 1).
Non‐relativistic quantum scattering from non‐local separable potentials: the eigenchannel approach
Authors: Augusiak R. 
Published: June 2022

AbstractA recently formulated version of the eigenchannel method [R. Szmytkowski, Ann. Phys. (N.Y.) 311, 503 (2004)] is applied to quantum scattering of Schrödinger particles from non‐local separable potentials. Eigenchannel vectors and negative cotangents of eigenphase‐shifts are introduced as eigensolutions to some weighted matrix spectral problem, without a necessity of prior construction and diagonalization of the scattering matrix. Explicit expressions for the scattering amplitude, the total cross section in terms of the eigenchannel vectors and the eigenphase‐shifts are derived. An illustrative example is provided.
Modeling Na clusters in Ar matrices
Authors: Fehrer F. , Mundt M. , Reinhard P.‐G. , Suraud E. 
Published: June 2022

AbstractWe present a microscopic model for Na clusters embedded in raregas matrices. The valence electrons of the Na cluster are described by time‐dependent density‐functional theory at the level of the local‐density approximation (LDA). Particular attention is paid to the semi‐classical picture in terms of Vlasov‐LDA. The Na+ ions and Ar atoms are handled as classical particles whereby the Ar atoms carry two degrees of freedom, position and dipole polarization. The interaction between Na+ ions and electrons is mediated through local pseudo‐potentials. The coupling to the Ar atoms is described by (long‐range) polarization potentials and (short‐range) repulsive cores. The ingredients are taken from elsewhere developed standards. A final fine‐tuning is performed using the NaAr molecule as benchmark. The model is then applied to embedded systems Na8ArN. By close comparison with quantum‐mechanical results, we explore the capability of the Vlasov‐LDA to describe such embedded clusters. We show that one can obtain a reasonable description by appropriate adjustments in the fine‐tuning phase of the model.
Gravity and the quantum vacuum inertia hypothesis
Authors: Rueda A. , Haisch B. 
Published: June 2022

AbstractIn previous work it has been shown that the electromagnetic quantum vacuum, or electromagnetic zero‐point field, makes a contribution to the inertial reaction force on an accelerated object. We show that the result for inertial mass can be extended to passive gravitational mass. As a consequence the weak equivalence principle, which equates inertial to passive gravitational mass, appears to be explainable. This in turn leads to a straightforward derivation of the classical Newtonian gravitational force. We call the inertia and gravitation connection with the vacuum fields the quantum vacuum inertia hypothesis. To date only the electromagnetic field has been considered. It remains to extend the hypothesis to the effects of the vacuum fields of the other interactions. We propose an idealized experiment involving a cavity resonator which, in principle, would test the hypothesis for the simple case in which only electromagnetic interactions are involved. This test also suggests a basis for the free parameter η(ν) which we have previously defined to parametrize the interaction between charge and the electromagnetic zero‐point field contributing to the inertial mass of a particle or object.
Semiclassical quantum gravity: statistics of combinatorial Riemannian geometries
Authors: Bombelli L. , Corichi A. , Winkler O. 
Published: June 2022

AbstractThis paper is a contribution to the development of a framework, to be used in the context of semiclassical canonical quantum gravity, in which to frame questions about the correspondence between discrete spacetime structures at “quantum scales” and continuum, classical geometries at large scales. Such a correspondence can be meaningfully established when one has a “semiclassical” state in the underlying quantum gravity theory, and the uncertainties in the correspondence arise both from quantum fluctuations in this state and from the kinematical procedure of matching a smooth geometry to a discrete one. We focus on the latter type of uncertainty, and suggest the use of statistical geometry as a way to quantify it. With a cell complex as an example of discrete structure, we discuss how to construct quantities that define a smooth geometry, and how to estimate the associated uncertainties. We also comment briefly on how to combine our results with uncertainties in the underlying quantum state, and on their use when considering phenomenological aspects of quantum gravity.
Ca‐doped Ba2Cu3O7–δ bicrystal junctions fabricated on asymmetric SrTiO3 substrates
Authors: Malisa A. 
Published: June 2022

AbstractBicrystal grain–boundary Josephson junctions of Ca–doped YBa2Cu3O7–δ that is Y0.7Ca0.3Ba2Cu3O7–δ were fabricated on three bicrystal SrTiO3 (001) substrates with asymmetric 30°, 40° and 45° orientations. An enhancement of the critical current density in these Ca–doped junctions was observed when compared with normal YBCO grain–boundary junctions with similar angular orientations. The observed increase in the critical current density is large for the junctions fabricated on the asymmetric 30° bicrystal substrate and small or negligible, for those on the asymmetric 45° bicrystal substrate. The critical current was modulated by a magnetic field applied in the plane of the junctions. However, the Fraunhofer pattern observed due to the applied magnetic field deviates from the ideal one.
Magnetic and quasiparticle excitations in cuprates
Authors: Bennemann K.‐H. 
Published: June 2022

AbstractDedicated to Bernhard Mühlschlegel on the occasion of his 80th birthdayAssuming for simplicity that the electrons or the holes in cuprate superconductors interact predominantly with spin‐fluctuations, we determine within the random phase approximation (RPA)the dynamical susceptibility, in particular the resonance peak resulting as feedback from superconductivity, as well as the elementary quasiparticle excitations in hole‐doped systems.
Orbital order, anisotropic spin couplings, and the spin‐wave spectrum of the ferromagnetic Mott insulator YTiO3
Authors: Schmitz R. , Entin‐Wohlman O. , Aharony A. , Müller‐Hartmann E. 
Published: June 2022

AbstractDedicated to Bernhard Mühlschlegel on the occasion of his 80th birthdayUsing a point‐charge calculation of the electrostatic crystal field, we determine the non‐degenerate orbital ground state of the ferromagnetic Mott insulator YTiO3, which is found to agree perfectly with experiment. Based on the orbital order, we obtain by perturbation theory an effective spin Hamiltonian that describes the magnetic superexchange between nearest‐neighbor Ti ions. The superexchange Hamiltonian includes, in addition to the isotropic Heisenberg coupling, antisymmetric (Dzyaloshinskii‐Moriya) and symmetric anisotropy terms, caused by the spin‐orbit interaction on the Ti ions. We find ferromagnetic Heisenberg couplings for Ti–Ti bonds in the crystallographic ab planes, but antiferromagnetic ones for Ti–Ti bonds between planes, in contradiction with experiment (which gives ferromagnetic couplings for both). Difficulties in calculating realistic values for the isotropic couplings of YTiO3 have been already reported in the literature. We discuss possible origins for these discrepancies. However, the much smaller values we obtain for the symmetric and antisymmetric anisotropies may be expected to be reliable. We therefore combine the experimentally‐deduced isotropic coupling with the calculated anisotropic ones to determine the magnetic order of the Ti ions, which is found to be in satisfactory agreement with experiment. Based on this magnetic order, we derive the spin‐wave spectrum. We find an acoustic branch with a very small zone‐center gap and three optical spin‐wave modes with sizeable zone‐center gaps. The acoustic branch reproduces the one reported in experiment, and the optical ones are in a satisfactory agreement with experiment, upon a proper folding of the magnetic Brillouin zone.
“Superluminal” phenomena can be attributed to instantaneous transfer of excitations in the near field zone
Authors: Perel'man M.E. 
Published: June 2022

AbstractThe observation of superluminal transmission of photons created discussions of their reality and significance. To analyze the possibility of such phenomena in general, the most general method is employed based on the covariant theory of dispersion relations. It is shown that superluminal phenomena can only be realized as tunneling of excitations within the near field zone. On this basis, the main experimental data can be described as sequential processes of single photon scattering. Their temporal distribution is estimated by taking into account the scattering time. Thus, the difference is explained between the advance of the superluminal part of the light pulse (i.e., the transition time of single photons) and the signal velocity of the macroscopic pulse of light.
Absence of weak electron localization in (Co/Pt)n‐multilayer‐nanowires with perpendicular anisotropy
Authors: Brands M. , Carl A. , Dumpich G. 
Published: June 2022

AbstractWe report on low temperature resistance and magnetoresistance (MR) measurements for various (Co/Pt)n‐multilayer‐nanowires with perpendicular magnetic anisotropy and different widths, designed as model systems for the experimental observation of weak electron localization effects in ferromagnetic systems as proposed by Dugaev et al. [Phys. Rev. B 64, 144423 (2001)]. The low temperature MR is found to originate from both the anisotropic MR and domain wall scattering. The temperature dependence of the resistance shows a logarithmic resistance increase with decreasing temperature, as it is typical for quantum corrections in two dimensional systems. Upon application of a perpendicular magnetic field, however, the slope of the logarithmic resistance increase does not change in magnitude, which proofs that weak localization effects are not present, at least within the accuracy of our measurements. Instead, the observed quantum corrections of the resistance are well explained by enhanced electron‐electron interaction effects in two dimensions. The results are discussed with regard to recent experimental as well as theoretical works.
Spin equation and its solutions
Authors: Bagrov V.G. , Gitman D.M. , Baldiotti M.C. , Levin A.D. 
Published: June 2022

AbstractThe aim of the present article is to study in detail the so‐called spin equation (SE) and present both the methods of generating new solution and a new set of exact solutions. We recall that the SE with a real external field can be treated as a reduction of the Pauli equation to the (0+1)‐dimensional case. Two‐level systems can be described by an SE with a particular form of the external field. In this article, we also consider associated equations that are equivalent or (in one way or another) related to the SE. We describe the general solution of the SE and solve the inverse problem for this equation. We construct the evolution operator for the SE and consider methods of generating new sets of exact solutions. Finally, we find a new set of exact solutions of the SE.
Was Einstein right?
Authors: Will C.M. 
Published: June 2022

AbstractWe review the experimental evidence for Einstein's special and general relativity. A variety of high precision null experiments verify the weak equivalence principle and local Lorentz invariance, while gravitational redshift and other clock experiments support local position invariance. Together these results confirm the Einstein Equivalence Principle which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak‐field, post‐Newtonian limit of metric theories strongly favor general relativity. The Binary Pulsar provides tests of gravitational‐wave damping and of strong‐field general relativity. Recently discovered binary pulsar systems may provide additional tests. Future and ongoing experiments, such as the Gravity Probe B Gyroscope Experiment, satellite tests of the Equivalence Principle, and tests of gravity at short distance to look for extra spatial dimensions could constrain extensions of general relativity. Laser interferometric gravitational‐wave observatories on Earth and in space may provide new tests of gravitational theory via detailed measurements of the properties of gravitational waves.