bluuebunny/crossref_metadata_2025_split huggingface dataset:
Koopman‐von Neumann formulation of classical Yang‐Mills theories: I
Authors: Carta P. , Gozzi E. , Mauro D. 
Published: June 2022

AbstractIn this paper we present the Koopman‐von Neumann (KvN) formulation of classical non‐Abelian gauge field theories. In particular we shall explore the functional (or classical path integral) counterpart of the KvN method. In the quantum path integral quantization of Yang‐Mills theories concepts like gauge‐fixing and Faddeev‐Popov determinant appear in a quite natural way. We will prove that these same objects are needed also in this classical path integral formulation for Yang‐Mills theories. We shall also explore the classical path integral counterpart of the BFV formalism and build all the associated universal and gauge charges. These last are quite different from the analog quantum ones and we shall show the relation between the two. This paper lays the foundation of this formalism which, due to the many auxiliary fields present, is rather heavy. Applications to specific topics outlined in the paper will appear in later publications.
Future state of the universe
Authors: Da̧browski M. P. 
Published: June 2022

AbstractFollowing the observational evidence for cosmic acceleration which may exclude a possibility for the universe to recollapse to a second singularity, we review alternative scenarios of its future evolution. Although the de Sitter asymptotic state is still an option, some other asymptotic states which allow new types of singularities such as Big‐Rip (due to a phantom matter) and sudden future singularities are also admissible and are reviewed in detail. The reality of these singularities which comes from the relation to observational characteristics of the universe expansion are also revealed and widely discussed.
Liouville and Fokker–Planck dynamics for classical plasmas and radiation
Authors: Alvarez‐Estrada R.F. 
Published: June 2022

AbstractWe consider a nonequilibrium statistical system formed by many classical non‐relativistic particles of opposite electric charges (plasma) and by the classical dynamical electromagnetic (EM) field. The charges interact with one another directly through instantaneous Coulomb potentials and with the dynamical degrees of freedom of the transverse EM field. The system may also be subject to external influences of: i) either static, but spatially inhomogeneous, electric and magnetic fields (case 1)), or ii) weak distributions of electric charges and currents (case 2)). The particles and the dynamical EM field are described, for any time t > 0, by the classical phase‐space probability distribution functional (CPSPDF) f and, at the initial time (t = 0), by the initial CPSPDF fin. The CPSPDF f and fin, multiplied by suitable Hermite polynomials (for particles and field) and integrated over all canonical momenta, yield new moments. The Liouville equation and fin imply a new nonequilibrium linear infinite hierarchy for the moments. In case 1), fin describes local equilibrium but global nonequilibrium, and we propose a long‐time approximation in the hierarchy, which introduces irreversibility and relaxation towards global thermal equilibrium. In case 2), the statistical system, having been at global thermal equilibrium, without external influences, for t ≤ 0, is subject to weak external charge‐current distributions: then, new hierarchies for moments and their long‐time behaviours are discussed in outline. As examples, approximate mean‐field (Vlasov) approximations are treated for both cases 1) and 2).
Paul Drude (1863–1906)*
Authors: Hoffmann D. 
Published: June 2022

AbstractIn July 1906 the physics community in Germany was shocked by the sudden death of Paul Drude, one of the key figures of a flourishing field. At the age of almost 43 years he had reached the summit of his career, having just been promoted to Director of the Physics Institute in Berlin and member of the Prussian Academy of Sciences. In the course of his academic research Drude covered the observation of macroscopic phenomena as well as the understanding of microscopic processes; he developed advanced methods to acquire reliable experimental data but also unified mathematical descriptions; he covered thermodynamics and statistical physics as well as optics and transport theory. Being always well grounded in classical physics he was also one of the first modern physicists.
Dynamic conductivity from audio to optical frequencies of semiconducting manganites approaching the metal‐insulator transition *
Authors: Lunkenheimer P. , Mayr F. , Loidl A. 
Published: June 2022

AbstractWe report the frequency‐dependent conductivity of the manganite system La1‐xSrxMnO3 (x≤0.2) when approaching the metal‐insulator transition from the insulating side. Results from low‐frequency dielectric measurements are combined with spectra in the infrared region. For low doping levels the behavior is dominated by hopping transport of localized charge carriers at low frequencies and by phononic and electronic excitations in the infrared region. For the higher Sr contents the approach of the metallic state is accompanied by the successive suppression of the hopping contribution at low frequencies and by the development of polaronic excitations in the infrared region, which finally become superimposed by a strong Drude contribution in the fully metallic state.
Inter‐band effects of magnetic field on orbital susceptibility and Hall conductivity – case of bismuth *
Authors: Fukuyama H. 
Published: June 2022

AbstractInterband effects of magnetic field on oribital susceptibility and Hall conductivity have been theoretically studied with special reference to single crystal bismuth (Bi), whose energy bands near the band‐edges are similar to those of Dirac electrons. It has long been known that orbital susceptibilty in Bi has a maximum when the Fermi energy is located in the band‐gap and then the density of states at the Fermi energy is vanishing. This implies that the magnetic field induces persisitint current even in the insulating state. On the other hand, weak‐field Hall conducctivity, which reflects transport current, has turned out to be vanishing if the Fermi energy is in the band‐gap. Interesting possibility has been pointed out of the inter‐band contributions to the Hall conductivity once the Fermi energy lies slightly in the energy band.
Optical conductivity of clean metals *
Authors: Rosch A. 
Published: June 2022

AbstractWe briefly review some basic aspects of transport in clean metals focusing on the role of electron‐electron interactions and neglecting the effects of impurities, phonons and interband transitions. Both for small Fermi surfaces of two and three‐dimensional metals and open Fermi surfaces of quasi one‐dimensional metals the dc conductivity σ is largely dominated by momentum and pseudo‐momentum conservation, respectively. In general, the frequency and temperature dependencies of σ(o,T) have very little in common. For small Fermi surfaces in three dimensions we find for example that the scattering rate is quadratic in frequency, Γ ∝ o2, even in the absence of a T2 contribution.
Optical conductivity to probe boson structure*
Authors: Carbotte J.P. , Schachinger E. 
Published: June 2022

AbstractThe phonon structure in optical data can be inverted to obtain the transport electron‐phonon spectral density α2Ftr(o). For more general electron‐boson exchange models we test the accuracy of using Allen's approximate relationship between spectral density and optical scattering rate instead of complete Eliashberg equation results. Both,s‐wave and d‐wave superconducting gap symmetries are considered.
Einstein Lecture – Passion for precision*
Authors: Hänsch T.W. 
Published: June 2022

AbstractOptical frequency combs from mode‐locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective.
Angular momenta and eigenvectors of the weakly coupled T ⊗ t Jahn‐Teller system
Authors: Barentzen H. 
Published: June 2022

AbstractThe eigenvalues of the weakly coupled T ⊗ t Jahn‐Teller problem are known for several decades, and the same holds also true for the eigenstates. These, however, are only given in the traditional position representation, which proves inconvenient if one attempts to extend the weak‐coupling treatment into the region of stronger coupling. Here the solution of the T ⊗ t eigenvalue problem at weak coupling is derived in terms of creation and annihilation operators. This reformulation of the problem is nontrivial, since the algebraic form of the oscillator eigenvectors, being simultaneous angular‐momentum eigenstates, has been worked out only recently and is probably still widely unknown. The electronic and oscillator eigenstates are then coupled to form eigenvectors of the total angular momentum. Finally, in preparation for an extension of the weak‐coupling treatment, the action of the boson creation and annihilation operators on the oscillator eigenvectors is calculated, thus completing the algebraic approach to the weakly coupled T ⊗ t system.
Negative refraction and quantum vacuum effects in gyroelectric chiral medium and anisotropic magnetoelectric material
Authors: Shen J.Q. , Norgren M. , He S. 
Published: June 2022

AbstractSome nontrivial effects (negative refraction and quantum vacuum effects) in gyroelectric chiral medium and magnetoelectric material are studied. It is shown that the refractive indices corresponding to some of the eigen modes in the gyroelectric chiral medium and magnetoelectric material may have negative real parts since both the gyroelectric and magnetoelectric parameters can dramatically reduce the refractive indices in certain frequency bands. As an anisotropic electromagnetic environment could be created due to the breaking of universal symmetry of vacuum mode distribution (and hence the noncompensation effect of a pair of counter‐propagating vacuum modes arises) inside the magnetoelectric material, the quantum vacuum in such an anisotropic electromagnetic environment may have a nonzero angular momentum. A novel quantum vacuum effect (angular momentum transfer between the quantum vacuum and the anisotropic magnetoelectric material) that may accompany the effect of magnetoelectric negative refraction is suggested. Such a nontrivial effect can be utilized to design sensitive, accurate measurement techniques, e.g., nanoscale‐sensitivity sensor.
Dynamical adjustment of propagators in Renormalization Group flows
Authors: Salmhofer M. 
Published: June 2022

AbstractA class of continuous renormalization group flows with a dynamical adjustment of the propagator is introduced and studied theoretically for fermionic and bosonic quantum field theories. The adjustment allows to include self–energy effects nontrivially in the denominator of the propagator and to adapt the scale decomposition to a moving singularity, and hence to define flows of Fermi surfaces in a natural way. These flows require no counterterms, but the counterterms used in earlier treatments can be constructed using them. The influence of propagator adjustment on the strong–coupling behaviour of flows is examined for a simple example, and some conclusions about the strong coupling behaviour of renormalization group flows are drawn.
On linear electromagnetic constitutive laws that define almost‐complex structures
Authors: Delphenich D.H. 
Published: June 2022

AbstractIt is shown that not all linear electromagnetic constitutive laws will define almost‐complex structures on the bundle of 2‐forms on the spacetime manifold when composed with the Poincaré duality isomorphism, but only a restricted class of them that includes linear spatially isotropic and some bi‐isotropic constitutive laws. Although this result does not trivialize the formulation of the basic equations of pre‐metric electromagnetism, it does affect their reduction to metric electromagnetism by its effect on the types of media that are reducible, and possibly its effect on the way that such media support the propagation of electromagnetic waves.
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

AbstractAfter discovering a subtle sign error in our previous work we have redone our calculations of the superexchange couplings in the ferromagnetic Mott insulator YTiO3. In contrast to the earlier result, the corrected calculations give realistic ferromagnetic Heisenberg couplings for Ti–Ti bonds in the crystallographic ab planes as well as along the c direction. The calculated antisymmetric (Dzyaloshinskii‐Moriya) and symmetric anisotropy terms of the superexchange Hamiltonian are also modified. Based on the calculated superexchange couplings we determine the magnetic order of the Ti ions and the spin‐wave spectrum, and both are found in acceptable agreement with experiment. Our model, in which the orbital degrees of freedom are frozen by the crystal field, also reproduces the experimentally observed orbital ordering pattern of the Ti ions. Therefore, this model provides a consistent picture of the orbital and of the magnetic ordering mechanisms in YTiO3. These mechanisms are coupled together, and have been a subject of considerable debate.
Semiclassical expansion of quantum characteristics for many‐body potential scattering problem
Authors: Krivoruchenko M.I. , Fuchs C. , Faessler A. 
Published: June 2022

AbstractIn quantum mechanics, systems can be described in phase space in terms of the Wigner function and the star‐product operation. Quantum characteristics, which appear in the Heisenberg picture as the Weyl's symbols of operators of canonical coordinates and momenta, can be used to solve the evolution equations for symbols of other operators acting in the Hilbert space. To any fixed order in the Planck's constant, many‐body potential scattering problem simplifies to a statistical‐mechanical problem of computing an ensemble of quantum characteristics and their derivatives with respect to the initial canonical coordinates and momenta. The reduction to a system of ordinary differential equations pertains rigorously at any fixed order in ħ. We present semiclassical expansion of quantum characteristics for many‐body scattering problem and provide tools for calculation of average values of time‐dependent physical observables and cross sections. The method of quantum characteristics admits the consistent incorporation of specific quantum effects, such as non‐locality and coherence in propagation of particles, into the semiclassical transport models. We formulate the principle of stationary action for quantum Hamilton's equations and give quantum‐mechanical extensions of the Liouville theorem on conservation of the phase‐space volume and the Poincaré theorem on conservation of 2p‐forms. The lowest order quantum corrections to the Kepler periodic orbits are constructed. These corrections show the resonance behavior.
A more direct representation for complex relativity
Authors: Delphenich D.H. 
Published: June 2022

AbstractAn alternative to the representation of complex relativity by self‐dual complex 2‐forms on the spacetime manifold is presented by assuming that the bundle of real 2‐forms is given an almost‐complex structure. From this, one can define a complex orthogonal structure on the bundle of 2‐forms, which results in a more direct representation of the complex orthogonal group in three complex dimensions. The geometrical foundations of general relativity are then presented in terms of the bundle of oriented complex orthogonal 3‐frames on the bundle of 2‐forms in a manner that essentially parallels their construction in terms of self‐dual complex 2‐forms. It is shown that one can still discuss the Debever‐Penrose classification of the Riemannian curvature tensor in terms of the representation presented here.
Close coupling approach in optically allowed atomic transitions
Authors: Bougouffa S. 
Published: June 2022

AbstractIn general the calculations of the cross sections in atomic collisions theory need a treatment of a system of coupled integro‐differential equations. We perform a numerical technique for calculations of electrons scattering with sodium atom. The cross sections are evaluated in the close coupling approach, where the problem is formulated in three coupling channel approximation. It is found that the three‐channel problem results are typically in good agreement with experiment and two‐channel calculations for intermediate energy range.The difference in the other range of energy can be assigned to the number of the used set of coupled differential equations in the 32S ↞ 32P transition of sodium.
A scheme for distributed quantum search through simultaneous state transfer mechanism
Authors: Gupta M. , Pathak A. 
Published: June 2022

AbstractUsing a quantum network model, we present a scheme for distributed implementation of Grover's algorithm. The proposed scheme can implement a quantum search over data bases stored in different computers. Entanglement is used to carry out different non‐local operations over the spatially distributed quantum computers. A method to transfer the combined state of many qubits over the entanglement and subsequently refreshing the entangled pair is presented. This method of simultaneous s tate transfer from one computer to the other, is shown to result in a constant communication complexity.
Nonlocal Lagrangians for accelerated systems
Authors: Chicone C. , Mashhoon B. 
Published: June 2022

AbstractAcceleration‐induced nonlocality and the corresponding Lorentz‐invariant nonlocal field equations of accelerated systems in Minkowski spacetime are discussed. Under physically reasonable conditions, the nonlocal equation of motion of the field can be derived from a variational principle of stationary action involving a nonlocal Lagrangian that is simply obtained by composing the local inertial Lagrangian with the nonlocal transformation of the field to the accelerated system. The implications of this approach for the electromagnetic and Dirac fields are briefly discussed.
An unknown story: Majorana and the Pauli‐Weisskopf scalar electrodynamics
Authors: Esposito S. 
Published: June 2022

AbstractAn account is given of an interesting but unknown theory by Majorana regarding scalar quantum electrodynamics, elaborated several years before the known Pauli‐Weisskopf theory. Theoretical calculations and their interpretation are given in detail, together with a general historical discussion of the main steps towards the building of a quantum field theory for electrodynamics. A possible peculiar application to nuclear constitution, as conceived around 1930, considered by Majorana is as well discussed.
Algebraic decomposition of the electromagnetic constitutive tensor. A step towards a pre‐metric based gravitation?
Authors: Matagne E. 
Published: June 2022

AbstractThe aim of this paper is to provide an algebraic decomposition of the principal part of the electromagnetic constitutive tensor χμνρσ (a pre‐metric structure), in a sum of terms of the form

where the Z(i) are invariant scalars and gμν(i)unimodular conformal metrics. If the space‐time is also equipped with a volume measure, such a decomposition is equivalent to a similar decomposition of the associated area metric, where the gμν(i) are ordinary metrics. It has been recently argued [8] that, if such a particular decomposition should be available, it would then be possible to find a compatible connection and derived tensors.
Geodesic‐invariant equations of gravitation
Authors: Verozub L. 
Published: June 2022

AbstractEinstein's equations of gravitation are not invariant under geodesic mappings, i.e. under a certain class of mappings of the Christoffel symbols and the metric tensor which leave the geodesic equations in a given coordinate system invariant. A theory in which geodesic mappings play the role of gauge transformations is considered.
Feedback control in flashing ratchets*
Authors: Craig E.M. , Kuwada N.J. , Lopez B.J. , Linke H. 
Published: June 2022

AbstractA flashing ratchet uses a time‐dependent, spatially periodic, asymmetric potential to rectify thermal motion of Brownian particles. Here we review approaches to improve the particle flux in this type of Brownian motor by feedback strategies that switch the potential based on the instantaneous particle distribution. We review strategies that are based on the force experienced by the particles, and introduce a new feedback strategy that is based on the expected displacement that can be achieved. Langevin dynamics simulations show that this maximum net displacement strategy performs better than force‐based strategies in the limit of very small particle numbers and not too high temperatures. We also review the effects of time delay and noisy channels on feedback control, and perform a feasibility analysis of an experimental system that can realize feedback control using a computer‐controlled, scanning‐line optical trap and suspended microspheres.
Option pricing theory for financial assets with memory*
Authors: Schulz M. 
Published: June 2022

AbstractDiffusion processes play an important role in physics as well as in financial sciences. The usual description by stochstic differential equations considers the Wiener process as external stochastic term, while the deterministic drift term is local in time. However, the complexity of the interaction between the observed diffusive degree of freedom and the hidden dynamics of the whole system, e.g., the coupling between a certain particle and the surrounding liquid or the relations between the price of a financial asset and the global market, requires the consideration of possible memory effects.In the present paper we analyze the effects of a non‐Markovian asset price model on the corresponding European option prices. This model considers drift terms which are non‐local in time, so that memory effects appear. As the main result we present a generalized Black‐Scholes equation considering the whole history of the asset price evolution.
Recent developments in quantum key distribution: Theory and practice*
Authors: Mauerer W. , Helwig W. , Silberhorn Ch. 
Published: June 2022

AbstractQuantum key distribution is among the foremost applications of quantum mechanics, both in terms of fundamental physics and as a technology on the brink of commercial deployment. Starting from principal schemes and initial proofs of unconditional security for perfect systems, much effort has gone into providing secure schemes which can cope with numerous experimental imperfections unavoidable in real world implementations. In this paper, we provide a comparison of various schemes and protocols. We analyse their efficiency and performance when implemented with imperfect physical components. We consider how experimental faults are accounted for using effective parameters. We compare various recent protocols and provide guidelines as to which components propose best advances when being improved.