bluuebunny/crossref_metadata_2025 huggingface dataset:
The dual curvature tensors and dynamics of gravitomagnetic matter
Authors: Shen J.Q.
Published: June 2022

Gravitomagnetic charge that can also be referred to as the dual mass or magnetic mass is the topological charge in gravity theory. A gravitomagnetic monopole at rest can produce a stationary gravitomagnetic field. Due to the topological nature of gravitomagnetic charge, the metric of spacetime where the gravitomagnetic matter is present will be nonanalytic. In this paper both the dual curvature tensors (which can characterize the dynamics of gravitational charge/monopoles) and the antisymmetric gravitational field equation of gravitomagnetic matter are presented. We consider and discuss the mathematical formulation and physical properties of the dual curvature tensors and scalar, antisymmetric source tensors, dual spin connection (including the low‐motion weak‐field approximation), dual vierbein field as well as dual current densities of gravitomagnetic charge. It is shown that the dynamics of gravitomagnetic charge can be founded within the framework of the above dual quantities. In addition, the duality relationship in the dynamical theories between the gravitomagnetic charge (dual mass) and the gravitoelectric charge (mass) is also taken into account in the present paper.
On gravitational radiation and the energy flux of matter
Authors: Maluf J.W. , Faria F.F.
Published: June 2022

A suitable derivative of Einstein's equations in the framework of the teleparallel equivalent of general relativity (TEGR) yields a continuity equation for the gravitational energy‐momentum. In particular, the time derivative of the total gravitational energy is given by the sum of the total fluxes of gravitational and matter fields energy. We carry out a detailed analysis of the continuity equation in the context of Bondi and Vaidya's metrics. In the former space‐time the flux of gravitational energy is given by the well known expression in terms of the square of the news function. It is known that the energy definition in the realm of the TEGR yields the ADM (Arnowitt‐Deser‐Misner) energy for appropriate boundary conditions. Here we show that the same energy definition also describes the Bondi energy. The analysis of the continuity equation in Vaidya's space‐time shows that the variation of the total gravitational energy is determined by the energy flux of matter only.
On the correspondence between a screw dislocation in gradient elasticity and a regularized vortex
Authors: Lazar M.
Published: June 2022

We show the correspondence between a screw dislocation in gradient elasticity and a regularized vortex. The effective Burgers vector, nonsingular distortion and stress fields of a screw dislocation and the effective circulation, smoothed velocity and momentum of a vortex are given and discussed.
The 2‐matrix of the spin‐polarized electron gas: contraction of sum rules and spectral resolutions*
Authors: Ziesche P. , Tasnádi F.
Published: June 2022

See original Ann. Phys. (Leipzig) 13, 124 (2004)
Reduced density matrices, their spectral resolutions, and the Kimball‐Overhauser approach*
Authors: Ziesche P. , Tasnádi F.
Published: June 2022

See original Ann. Phys. (Leipzig) 13, 232 (2004)
Deep inside the pion. Reconciling QCD theory with data *
Authors: Bakulev A.P. , Mikhailov S.V. , Stefanis N.G.
Published: June 2022

Recent developments in the QCD description of the pion structure are reviewed. The CLEO pion‐photon transition data analysis favors a distribution amplitude for the pion that is double‐humped but endpoint‐suppressed. After a short outline of the derivation of this amplitude from QCD sum rules with nonlocal condensates, we present the fully fledged analysis of the CLEO data prefaced by predictions for the Fγρπ form factor and commenting on the inherent theoretical uncertainties due to higher twists and NNLO perturbative corrections. We supplement our discussion by considering within QCD factorization theory, the electromagnetic pion form factor at NLO accuracy on one hand, and diffractive di‐jets production on the other, comparing our predictions with the respective experimental data from JLab and the Fermilab E791 collaboration. In all cases, the agreement is impressive.
Transversity in the chiral quark–soliton model and single spin asymmetries ***
Authors: Efremov A.V.
Published: June 2022

A short review of single spin asymmetries in deep inelastic semi‐inclusive processes, connected with prediction of chiral quark‐soliton model for the nucleon transversity distributions, its possible theoretical understanding in the framework of QCD‐induced approach and arising difficulties is given.
Some comments on the handbag approach to wide‐angle exclusive scattering*
Authors: Kroll P.
Published: June 2022

The handbag mechanism for wide‐angle exclusive scattering reactions is discussed and compared to other theoretical approaches. The role of power laws in observables is critically examined. Applications of the handbag mechanism to Compton scattering and meson photoproduction are presented. The soft physics input to these processes are specific form factors which represent 1/x moments of generalized parton distributions at zero skewness. A recent analysis of the nucleon form factors provides these GPDs and, hence, the new form factors.
Recent progress in the understanding of single spin asymmetries*
Authors: Metz A. , Schlegel M.
Published: June 2022

Over the past years a lot of progress has been made in the understanding of single spin asymmetries in hard scattering processes. We briefly review this subject, covering the non‐vanishing of time‐reversal odd parton distributions, universality of fragmentation functions, and the discovery of previously unknown time‐reversal odd parton distributions at subleading twist. Interestingly enough, all these developments were initiated by simple model calculations.
SU(3) constraints on cryptoexotic pentaquarks*
Authors: Praszałowicz M.
Published: June 2022

We examine SU(3) constraints on the spectrum and decay widths of cryptoexotic nucleon‐like states in antidecuplet of pentaquarks. We show that in the ideal mixing scenario the number of free matrix elements describing splittings reduces from 4 to 2. Model‐independent sum rules are derived. Using as input Θ+ and Ξ3/2 masses we show that it is difficult to interpret Roper and N*(1710) nucleon resonances as cryptoexotic pentaquarks. Large Nc limit for antidecuplet and accompanying octet in the diqaurk picture and the analogy with the soliton model is also discussed.
New insight into nuclear structure from QCD*
Authors: Thomas A.W.
Published: June 2022

The natural building blocks of atomic nuclei within the framework of QCD are colorless clusters of quarks, with the quantum numbers of nucleons but with internal structure modified by the local mean scalar field. A key parameter of the nucleon in such an approach is the scalar polarizability, which characterizes the response of a nucleon to an applied scalar field. This response leads naturally to 3‐, 4‐ and higher‐body effective forces, each proportional to a higher power of the scalar polarizabilty. Recent progress on the important problem of chiral extrapolation of lattice QCD data suggests a way to estimate the scalar polarizability of the nucleon, with initial results consistent with successful phenomenlogical estimates. This may be seen as a first step in the struggle to derive nuclear structure from QCD itself.
Generation of photons on demand using cavity quantum electrodynamics
Authors: Walther H.
Published: June 2022

The paper gives a survey on recent experiments on the deterministic generation of photons. Experiments using Rydberg atoms in microwave cavities and trapped ions in optical cavities are discussed. The latter experiments show that lasers on the basis of single atoms are possible.
Special Relativity and Lorentz Invariance
Authors: Lämmerzahl C.
Published: June 2022

Lorentz Invariance, the main ingredient of Special Relativity, is one of the pillars of modern physics. Though Special Relativity has been replaced by General Relativity, Lorentz Invariance is still valid locally. All physical fields have to obey the laws of local Lorentz Invariance. This is also the reason why gravity within the theory of General Relativity has to be described by the metric tensor. Here we give a short introduction into the early experiments and show that they disproved the exact validity of the Galilean framework for the description of classical mechanics. After a short summary of Special Relativity, the procedure of synchronization is analyzed. It is emphasized that no experiment should depend on the synchronization. Otherwise it might be possible to simulate or compensate effects by choosing another synchronization. Accordingly, the requirement of synchronization independence is a guideline for the choice of appropriate measurable quantities which then reveal relativistic physics in an unambiguous manner. Examples are given. In a subsequent article the modern experiments implementing this kind of notions will be discussed. Also some remarks are made on the importance of Lorentz Invariance in daily life. Finally we comment on possible violations of Lorentz Invariance and their measurability.
On the interaction of mesoscopic quantum systems with gravity
Authors: Kiefer C. , Weber C.
Published: June 2022

We review the different aspects of the interaction of mesoscopic quantum systems with gravitational fields. We first discuss briefly the foundations of general relativity and quantum mechanics. Then, we consider the non‐relativistic expansions of the Klein‐Gordon and Dirac equations in the post‐Newtonian approximation. After a short overview of classical gravitational waves, we discuss two proposed interaction mechanisms: (i) the use of quantum fluids as generator and/or detector of gravitational waves in the laboratory, and (ii) the inclusion of gravitomagnetic fields in the study of the properties of rotating superconductors. The foundations of the proposed experiments are explained and evaluated.
Tidal dynamics of relativistic flows near black holes
Authors: Chicone C. , Mashhoon B.
Published: June 2022

We point out novel consequences of general relativity involving tidal dynamics of ultrarelativistic relative motion. Specifically, we use the generalized Jacobi equation and its extension to study the force‐free dynamics of relativistic flows near a massive rotating source. We show that along the rotation axis of the gravitational source, relativistic tidal effects strongly decelerate an initially ultrarelativistic flow with respect to the ambient medium, contrary to Newtonian expectations. Moreover, an initially ultrarelativistic flow perpendicular to the axis of rotation is strongly accelerated by the relativistic tidal forces. The astrophysical implications of these results for jets and ultrahigh energy cosmic rays are briefly mentioned.
The relativistic energy spectrum of hydrogen
Authors: Marsch E.
Published: June 2022

The method originally used by Dirac to derive his equation for a single electron is here applied to the two‐particle system electron plus proton, considered as an elementary fermion, to obtain a relativistic two‐particle Dirac‐Breit‐type Hamiltonian for the hydrogen atom. This problem can be solved exactly. Thus the relativistic energy levels of the hydrogen atom as a system bound by the static Coulomb force are obtained. The radial part of the resulting Hamiltonian operates in a four‐dimensional space describing particles, respectively antiparticles, i. e. electron and positron as well as proton and antiproton. The spin of a particle is described by the normal two‐component Pauli spinor, and therefore standard theoretical tools for dealing with angular‐momentum coupling can be exploited. The classical energy states of the hydrogen atom are retained in the appropriate non‐relativistic limit, in particular the energy levels resulting from Schrödinger's equation. The exact energy spectrum shows the expected dependence on the reduced mass of the two‐particle system, and thus describes the recoil of the core properly. The fine structure of the hydrogen spectrum arises from a dependence of the energy levels upon the quantum number of the total angular momentum.
Spontaneous emission of light from atoms: the model
Authors: Marecki P. , Szpak N.
Published: June 2022

We investigate (non‐relativistic) atomic systems interacting with quantum electromagnetic field (QEF). The resulting model describes spontaneous emission of light from a two‐level atom surrounded by various initial states of the QEF. We assume that the quantum field interacts with the atom via the standard, minimal‐coupling Hamiltonian, with the A2 term neglected. We also assume that there will appear at most single excitations (photons). By conducting the analysis on a general level we allow for an arbitrary initial state of the QEF (which can be for instance: the vacuum, the ground state in a cavity, or the squeezed state). We derive a Volterra‐type equation which governs the time evolution of the amplitude of the excited state. The two‐point function of the initial state of the QEF, integrated with a combination of atomic wavefunctions, forms the kernel of this equation.
Proof of perturbative gauge invariance for tree diagrams to all orders
Authors: Dütsch M.
Published: June 2022

It is proved that classical BRS‐invariance of the Lagrangian implies perturbative gauge invariance for tree diagrams to all orders. The proof applies in particular to the Einstein Hilbert Lagrangian of gravity.
Non‐Volkov solutions for a charge in a plane wave
Authors: Bagrov V. , Gitman D.
Published: June 2022

As it is known, a set of solutions of the Klein‐Gordon and Dirac equations with a plane‐wave field was found for the first time by Volkov. We construct new solutions of these equations different from the Volkov ones. In particular, the new solutions are characterized by quantum numbers different from Volkov solutions. In fact, our result is based on the demonstration that the transversal charge motion in a plane wave can be mapped by a special quantum transformation to transversal free particle motion. Similarly, we find new sets of solutions of the Klein‐Gordon and Dirac equations with the combined electromagnetic field.
Massive supersymmetric quantum gauge theory
Authors: Grigore D.R. , Gut M. , Scharf G.
Published: June 2022

We continue the study of the supersymmetric vector multiplet in a purely quantum framework. We obtain some new results which make the connection with the standard literature. First we construct the one‐particle physical Hilbert space taking into account the (quantum) gauge structure of the model. Then we impose the condition of positivity for the scalar product only on the physical Hilbert space. Finally we obtain a full supersymmetric coupling which is gauge invariant in the supersymmetric sense in the first order of perturbation theory. By integrating out the Grassmann variables we get an interacting Lagrangian for a massive Yang‐Mills theory related to ordinary gauge theory; however the number of ghost fields is doubled so we do not obtain the same ghost couplings as in the standard model Lagrangian.
Effective descriptions of complex quantum systems: path integrals and operator ordering problems
Authors: Eckern U. , Gruber M.J. , Schwab P.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

We study certain aspects of the effective, occasionally called collective, description of complex quantum systems within the framework of the path integral formalism, in which the environment is integrated out. Generalising the standard Feynman‐Vernon Caldeira‐Leggett model to include a non‐linear coupling between “particle” and environment, and considering a particular spectral density of the coupling, a coordinate‐dependent mass (or velocity‐dependent potential) is obtained. The related effective quantum theory, which depends on the proper discretisation of the path integral, is derived and discussed. As a result, we find that in general a simple effective low‐energy Hamiltonian, in which only the coordinate‐dependent mass enters, cannot be formulated. The quantum theory of weakly coupled superconductors and the quantum dynamics of vortices in Josephson junction arrays are physical examples where these considerations, in principle, are of relevance.
Proximity effect between superconductors and ferromagnets: from thin films to nanostructures
Authors: v. Löhneysen H. , Beckmann D. , Pérez‐Willard F. , Schöck M. , Strunk C. , Sürgers C.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

Experimental investigations of superconductor/ferromagnet (S/F) interfaces which probe the penetration of the superconducting pairing amplitude into the ferromagnet are reviewed. The microscopic basis for this proximity effect is the process of Andreev reflection which can be used to extract the current spin‐polarization in F from current‐voltage characteristics. Initial studies focused on S/F layers and multilayers, while more recent experiments investigated nanostructured point contacts in local and nonlocal configurations.
Green functions for nearest‐ and next‐nearest‐neighbor hopping on the Bethe lattice
Authors: Kollar M. , Eckstein M. , Byczuk K. , Blümer N. , van Dongen P. , Radke de Cuba M.H. , Metzner W. , Tanasković D. , Dobrosavljević V. , Kotliar G. , Vollhardt D.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

We calculate the local Green function for a quantum‐mechanical particle with hopping between nearest and next‐nearest neighbors on the Bethe lattice, where the on‐site energies may alternate on sublattices. For infinite connectivity the renormalized perturbation expansion is carried out by counting all non‐self‐intersecting paths, leading to an implicit equation for the local Green function. By integrating out branches of the Bethe lattice the same equation is obtained from a path integral approach for the partition function. This also provides the local Green function for finite connectivity. Finally, a recently developed topological approach is extended to derive an operator identity which maps the problem onto the case of only nearest‐neighbor hopping. We find in particular that hopping between next‐nearest neighbors leads to an asymmetric spectrum with additional van‐Hove singularities.
Symmetries and pre‐metric electromagnetism
Authors: Delphenich D.H.
Published: June 2022

The equations of pre‐metric electromagnetism are formulated as an exterior differential system on the bundle of exterior differential 2‐forms over the spacetime manifold. The general form for the symmetry equations of the system is computed and then specialized to various possible forms for an electromagnetic constitutive law, namely, uniform linear, non‐uniform linear, and uniform nonlinear. It is shown that in the uniform linear case, one has four possible ways of prolonging the symmetry Lie algebra, including prolongation to a Lie algebra of infinitesimal projective transformations of a real four‐dimensional projective space. In the most general non‐uniform linear case, the effect of non‐uniformity on symmetry seems inconclusive in the absence of further specifics, and in the uniform nonlinear case, the overall difference from the uniform linear case amounts to a deformation of the electromagnetic constitutive tensor by the electromagnetic field strengths, which induces a corresponding deformation of the symmetry Lie algebra that was obtained in the linear uniform case.
The gravitational energy‐momentum tensor and the gravitational pressure
Authors: Maluf J.W.
Published: June 2022

In the framework of the teleparallel equivalent of general relativity it is possible to establish the energy‐momentum tensor of the gravitational field. This tensor has the following essential properties: (1) it is identified directly in Einstein's field equations; (2) it is conserved and traceless; (3) it yields expressions for the energy and momentum of the gravitational field; (4) is is free of second (and highest) derivatives of the field variables; (5) the gravitational and matter energy‐momentum tensors take place in the field equations on the same footing; (6) it is unique. However it is not symmetric. We show that the spatial components of this tensor yield a consistent definition of the gravitational pressure.
A gravitational mechanism for the acceleration of ultrarelativistic particles
Authors: Chicone C. , Mashhoon B.
Published: June 2022

Imagine a swarm of free particles near a point P outside a gravitating mass M and a free reference particle at P that is on a radial escape trajectory away from M. Relative to this reference particle and in a Fermi normal coordinate system constructed along its worldline, the particles in the swarm that move along the radial direction and are ultrarelativistic (that is, they have speeds above c/√2) decelerate toward this terminal speed. On the other hand, the swarm particles that are ultrarelativistic and move in directions normal to the radial (jet) directions accelerate to almost the speed of light by the gravitational tidal force of the mass M. The implications of these effects as well as the influence of the higher‐order terms on the tidal acceleration mechanism are investigated. The observational evidence in support of these general relativistic effects is briefly discussed.
Gravitational lensing as a powerful astrophysical tool: Multiple quasars, giant arcs and extrasolar planets
Authors: Wambsganss J.
Published: June 2022

In the 25 years since the discovery of the first double quasar Q0957+561, gravitational lensing has established itself as a valuable tool in many branches of astronomy. Fields as different as galactic structure, cosmology, or extrasolar planets benefit from the gravitational lensing effect. This article starts with a brief historic reflection, then the basics of light deflection are reviewed. Observable lensing effects and a few examples of strong lensing phenomena are shown. In the main part four applications of ''strong'' lensing will be presented and discussed:

The determination of the Hubble constant from time delay measurements in multiple quasars; it is argued that this method of determining H0 is competitive with other methods by now. The lensing‐derived values of H0 are on the low side.

Microlensing of quasars– the effects of compact stellar‐mass objects on the apparent brightness – allows us to constrain the quasar size and the occurrence of dark matter objects.

The frequency of giant luminous arcs strongly depends on the high mass end of the galaxy cluster distribution. Recent investigations show that arc statistics is in agreement with the concordance cosmological model.
Searching for extrasolar planets is one of the most recent applications of gravitational lensing. The first detection shows that the method works well. This planet‐search method is complementary to other programs and has the potential to detect exo‐planets with lower masses than other ground‐based techniques.

An outlook is provided on the prospects of gravitational lensing in the next few years. In particular the magnification effect on faint high‐redshift sources will be used for the investigation of the early universe, and the detection of low‐mass extrasolar planets will provide a valuable sample for statistical evaluations of the frequency of exoplanets.
Topological censorship and chronology protection
Authors: Friedman J. , Higuchi A.
Published: June 2022

Over the past two decades, substantial efforts have been made to understand the way in which physics enforces the ordinary topology and causal structure that we observe on observed scales – from subnuclear to cosmological. We review the status of topological censorship and the topology of event horizons; chronology protection in classical and semiclassical gravity; and related progress in establishing quantum energy inequalities.
Black holes surrounded by uniformly rotating rings
Authors: Petroff D. , Ansorg M.
Published: June 2022

This paper provides a brief summary of a talk on rings surrounding Black Holes that was given at the spring meeting 2005 of the German physical society (DPG). A detailed discussion of the topics covered in the talk can be found in [1].
Gauge fixing procedure in the extended BRST theory. The example of the abelian 2‐forms
Authors: Constantinescu R. , Ionescu C.
Published: June 2022

The paper proposes a general procedure to find the form of the gauge fixing term in the extended BRST quantization of the gauge theories, a difficult problem in the standard approach. Our proposal is based on the many level structure of the extended spaces and leads to a simple form of the gauge fixing term. The abelian 2‐form model is completely analyzed as an example.
Koopman‐von Neumann formulation of classical Yang‐Mills theories: I
Authors: Carta P. , Gozzi E. , Mauro D.
Published: June 2022

In 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.
Quantum cosmology: expectations and results
Authors: Kiefer C.
Published: June 2022

I critically review the status of quantum cosmology. The expectations on such a theory are compared with the obtained results. The issues being discussed include the role of boundary conditions, singularity avoidance, the quantum‐to‐classical transition and the origin of irreversibility, and structure formation.
Future state of the universe
Authors: Da̧browski M. P.
Published: June 2022

Following 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

We 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

In 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

We 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

Interband 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

We 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

The 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

Optical 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

The 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

Some 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

A 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

It 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

After 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

In 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

An 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.
Full counting statistics and field theory*
Authors: Nazarov Y.V.
Published: June 2022

We review the relations between the full counting statistics and the field theory of electric circuits. We demonstrate that for large conductances the counting statistics is determined by non‐trivial saddle‐point of the field. Coulomb effects in this limit are presented as quantum corrections that can strongly renormalize the action at low energies.
Close coupling approach in optically allowed atomic transitions
Authors: Bougouffa S.
Published: June 2022

In 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

Using 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

Acceleration‐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

An 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

The 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

Einstein'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

A 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.