bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivation of Poincaré invariance from general quantum field theory
Authors: Froggatt C.D. , Nielsen H.B.
Published: June 2022

Starting 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

In 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

We 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

We 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

We 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

Excited 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

The 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

A 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

We 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

In 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

This 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

Bicrystal 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

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

Assuming 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

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

Using 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

The 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

We 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

The 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

We 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.
Strong‐field tests of gravity with the double pulsar
Authors: Kramer M. , Stairs I.H. , Manchester R.N. , McLaughlin M.A. , Lyne A.G. , Ferdman R.D. , Burgay M. , Lorimer D.R. , Possenti A. , D'Amico N. , Sarkissian J. , Joshi B.C. , Freire P.C.C. , Camilo F.
Published: June 2022

This first‐ever double‐pulsar system was discovered in 2003, consisting of two visible pulsars which orbit the common centre of mass in a slightly eccentric orbit in only 2.4 hours. One of the pulsars appears to be old and recycled with a spin period of only 22 ms. Its companion is younger and rotating slower with a period of 2.8 s, confirming the long‐proposed recycling theory for millisecond pulsars. The system provides an exciting opportunity to study the workings of pulsar magnetospheres and represents a truly unique laboratory for relativistic gravitational physics. Both aspects are greatly facilitated by the very fortunate fact that the orbit is seen nearly perfectly edge on. This alignment allows the detection of the Shapiro delay in the pulse arrival times of the 22‐ms pulsar when its pulses propagate through the curved space‐time near the slowly rotating pulsar. In addition to updating on the continuing observations, this contribution introduces a new timing model that represents a variation of Damour‐Deruelle (1986) for highly inclined orbits.
Dark matter and galaxy formation
Authors: Silk J.
Published: June 2022

Dark matter presents a challenge for gravitational theory. It is best attacked in two ways; by studying the confrontation of structure formation with observation and by direct and indirect searches. In this review, I will focus on those aspects of dark matter that are relevant for understanding galaxy formation, and describe the outlook for detecting the most elusive component, non‐baryonic dark matter.
Is general relativity ‘essentially understood’? *
Authors: Friedrich H.
Published: June 2022

The content of Einstein's theory of gravitation is encoded in the properties of the solutions to his field equations. There has been obtained a wealth of information about these solutions in the ninety years the theory has been around. It led to the prediction and the observation of physical phenomena which confirm the important role of general relativity in physics. The understanding of the domain of highly dynamical, strong field configurations is, however, still quite limited. The gravitational wave experiments are likely to provide soon observational data on phenomena which are not accessible by other means. Further theoretical progress will require, however, new methods for the analysis and the numerical calculation of the solutions to Einstein's field equations on large scales and under general assumptions. We discuss some of the problems involved, describe the status of the field and recent results, and point out some open problems.
Projective geometry and special relativity
Authors: Delphenich D.H.
Published: June 2022

Some concepts of real and complex projective geometry are applied to the fundamental physical notions that relate to Minkowski space and the Lorentz group. In particular, it is shown that the transition from an infinite speed of propagation for light waves to a finite one entails the replacement of a hyperplane at infinity with a light cone and the replacement of an affine hyperplane – or rest space – with a proper time hyperboloid. The transition from the metric theory of electromagnetism to the pre‐metric theory is discussed in the context of complex projective geometry, and ultimately, it is proposed that the geometrical issues are more general than electromagnetism, namely, they pertain to the transition from point mechanics to wave mechanics.
Cosmologies from higher‐order string corrections
Authors: Tsujikawa S.
Published: June 2022

We study cosmologies based on low‐energy effective string theory with higher‐order string corrections to a tree‐level action and with a modulus scalar field (dilaton or compactification modulus). In the presence of such corrections it is possible to construct nonsingular cosmological solutions in the context of Pre‐Big‐Bang and Ekpyrotic universes. We review the construction of nonsingular bouncing solutions and resulting density perturbations in Pre‐Big‐Bang and Ekpyrotic models. We also discuss the effect of higher‐order string corrections on a dark energy universe and show several interesting possibilities of the avoidance of future singularities.
Dark energy: current issues
Authors: Polarski D.
Published: June 2022

The observed recent accelerated expansion of the Universe constitutes a dramatic departure from traditional views. The mechanism behind this accelerated expansion is still mysterious and is a major challenge to present‐day cosmology. Though it can be due to a new perfect fluid with negative pressure coined Dark Energy, it could also originate from modifications of gravity. We present some Dark Energy models in the context of General Relativity and review in some details the properties of Dark Energy models in scalar‐tensor gravity. We emphasize that observations probing both the background and the perturbations will constrain the proposed model most effectively.
No cross‐interactions between the Weyl graviton and the massless Rarita‐Schwinger field
Authors: Bizdadea C. , Cioroianu E.M. , Lungu A.C. , Săraru S.C.
Published: June 2022

The proof of the fact that there are no nontrivial, consistent cross‐couplings that can be added between the Weyl graviton and the massless Rarita‐Schwinger field is accomplished by means of a cohomological approach, based on the deformation of the solution to the master equation from the antifield‐Becchi‐Rouet‐Stora‐Tyutin (BRST) formalism. The procedure developed here relies on the assumptions of locality, smoothness, (background) Lorentz invariance, Poincaré invariance, and preservation of the number of derivatives with respect to each field (the last hypothesis was made only in antighost number zero).
Another century of ellipsometry*
Authors: Schubert M.
Published: June 2022

In commemoration of the inventor – Paul Karl Ludwig Drude – examples of contemporary interest in the vivid field of ellipsometry are presented. More than 100 years after his provision of the general concept and the first experimental application, ellipsometry has matured as tool‐of‐excellence in almost all materials research areas. This contribution reviews selected applications in solid‐state materials physics and engineering addressing state‐of‐the‐art ellipsometry concepts. Particular emphasis is placed on the generalized ellipsometry framework. Infrared ellipsometry and magnetooptic infrared ellipsometry provide access to yet another important achievement of Paul Drude in optical physics: The free electron model in conductors, but also clearly reveal deviations from thereof within charge‐correlated systems, exemplified here by the observation of Landau level splitting in two‐dimensional electron gases using synchrotron light source ellipsometry at terahertz frequencies.
Verifying the Drude response*
Authors: Dressel M. , Scheffler M.
Published: June 2022

By now more than 100 years passed since Paul Drude suggested his highly acclaimed model of electronic transport. In the form advanced by A. Sommerfeld, the Drude model is still heavily utilized to describe, for instance, the optical properties of metals. Surprisingly, the key prediction of the Drude model, the frequency dependence of the complex conductivity with its pronounced roll‐off was directly observed in an experiment only very recently. Here we present direct and independent measurements of both the real and imaginary parts of the metallic conductivity in a large range of frequency around the scattering rate.
Electrodynamics of correlated electron matter *
Authors: Dordevic S.V. , Basov D.N.
Published: June 2022

Infrared spectroscopy has emerged as a premier experimental technique to probe enigmatic effects arising from strong correlations in solids. Here we report on recent advances in this area focusing on common patterns in correlated electron systems including transition metal oxides, intermetallics and organic conductors. All these materials are highly conducting substances but their electrodynamic response is profoundly different from the canonical Drude behavior observed in simple metals. These unconventional properties can be attributed in several cases to the formation of spin and/or charge ordered states, zero temperature phase transitions and strong coupling to bosonic modes.
Superconducting fluctuations in Bi2Sr2Ca1‐xDyxCu2O8+δ as seen by terahertz spectroscopy *
Authors: Orenstein J. , Corson J. , Oh S. , Eckstein J.N.
Published: June 2022

More than one hundred years ago Paul Drude derived the frequency‐dependent conductivity σ(o) of a gas of point charges, showing that the width of the spectrum was related to the scattering rate of carriers. Seventy five years later, in the late 1970's and early 1980's, it was recognized that σ(o) of a two‐dimensional superconductor above it's transition temperature Tc could be described by the Drude response of interpenetrating gases of electrons and vortices. Here we describe measurements of σ(o) in the high‐Tc superconductor system Bi2Sr2Ca1‐xDyxCu2O8+δ (BSCCO) using time‐domain THz spectroscopy that provide evidence for vortices above Tc. We compare this evidence with results obtained by other probes of fluctuations in cuprate superconductors.
Drude behavior in the far‐infrared conductivity of cuprate superconductors
Authors: Liu H.L. , Quijada M. , Romero D.B. , Tanner D.B. , Zibold A. , Carr G.L. , Berger H. , Forró L. , Mihaly L. , Cao G. , O Beom‐Hoan , Markert J.T. , Rice J.P. , Burns M.J. , Delin K.A.
Published: June 2022

When viewed at frequencies below about 8 THz (250 cm‐1; 30 meV) the ab‐plane optical conductivity of the cuprate superconductors (in their normal state) is well described by a Drude model. Examples include optimally‐doped YBa2Cu3O7‐δ and Bi2Sr2CaCu2O8; even the underdoped phases have a Drude character to their optical conductivity. A residual Drude‐like normal fluid is seen in the superconducting state in most cases; the scattering rate of this quasiparticle contribution collapses at Tc.
Concerning the state‐change due to the measurement process***
Authors: Lüders G.
Published: June 2022

The statistical transformation theory contains procedures for the computation of measurement probabilities, but requires for its completion a statement about the state‐change due to the measurement process. We discuss and reject an ansatz suggested for this by J. von Neumann. We submit an ansatz for the state‐change which is essentially identical to the ‘reduction of the wave function’. It permits a deepening of the concept of compatibility of measurements. Finally, measurements of states subject to con straints are considered.
Gravitational model of the string
Authors: Dzhunushaliev V.
Published: June 2022

It is shown that an infinite gravitational flux tube solution in 5D Kaluza‐Klein gravity with the cross section in the Planck region after 5D ⇒ 4D reduction and isometrical embedding in a Minkowski spacetime can be considered as a moving infinite string‐like object. Such an object carries an electric and a magnetic flux. The 4D gravitational waves on the tube are considered.
From primordial quantum fluctuations to the anisotropies of the cosmic microwave background radiation *
Authors: Straumann N.
Published: June 2022

These lecture notes cover mainly three connected topics. In the first part we give a detailed treatment of cosmological perturbation theory. The second part is devoted to cosmological inflation and the generation of primordial fluctuations. In part three it will be shown how these initial perturbation evolve and produce the temperature anisotropies of the cosmic microwave background radiation. Comparing the theoretical prediction for the angular power spectrum with the increasingly accurate observations provides important cosmological information (cosmological parameters, initial conditions).
Supersymmetric Källen‐Lehmann representation
Authors: Constantinescu F.
Published: June 2022

We find the general form of supersymmetric invariant two point functions. By imposing supersymmetric positivity we obtain the general supersymmetric Källen‐Lehmann representation.
The Einstein–Cartan–Elko system
Authors: Böhmer C.G.
Published: June 2022

The present paper analyses the Einstein‐Cartan theory of gravitation with Elko spinors as sources of curvature and torsion. After minimally coupling the Elko spinors to torsion, the spin angular momentum tensor is derived and its structure is discussed. It shows a much richer structure than the Dirac analogue and hence it is demonstrated that spin one half particles do not necessarily yield only an axial vector torsion component. Moreover, it is argued that the presence of Elko spinors partially solves the problem of minimally coupling Maxwell fields to Einstein‐Cartan theory.
Exact solution of the Klein‐Gordon equation for the PT‐symmetric generalized Woods‐Saxon potential by the Nikiforov‐Uvarov method
Authors: Ikhdair S.M. , Sever R.
Published: June 2022

The exact solution of the one‐dimensional Klein‐Gordon equation of the 𝒫𝒯‐symmetric generalized Woods‐Saxon potential is obtained. The exact energy eigenvalues and wavefunctions are derived analytically by using the Nikiforov and Uvarov method. In addition, the positive and negative exact bound states of the s‐states are also investigated for different types of complex generalized Woods‐Saxon potentials.
The conformal status of o = ‐3/2 Brans‐Dicke cosmology
Authors: Da̧browski M.P. , Denkiewicz T. , Blaschke D.B.
Published: June 2022

Following recent fit of supernovae data to Brans‐Dicke theory which favours the model with o = ‐ 3/2 [1] we discuss the status of this special case of Brans‐Dicke cosmology in both isotropic and anisotropic framework. It emerges that the limit o = ‐3/2 is consistent only with the vacuum field equations and it makes such a Brans‐Dicke theory conformally invariant. Then it is an example of the conformal relativity theory which allows the invariance with respect to conformal transformations of the metric. Besides, Brans‐Dicke theory with o = ‐3/2 gives a border between a standard scalar field model and a ghost/phantom model. In this paper we show that in o = ‐3/2 Brans‐Dicke theory, i.e., in the conformal relativity there are no isotropic Friedmann solutions of non‐zero spatial curvature except for k=‐1 case. Further we show that this k=‐1 case, after the conformal transformation into the Einstein frame, is just the Milne universe and, as such, it is equivalent to Minkowski spacetime. It generally means that only flat models are fully consistent with the field equations. On the other hand, it is shown explicitly that the anisotropic non‐zero spatial curvature models of Kantowski‐Sachs type are admissible in o = ‐3/2 Brans‐Dicke theory. It then seems that an additional scale factor which appears in anisotropic models gives an extra deegre of freedom and makes it less restrictive than in an isotropic Friedmann case.
Two interacting spins in external fields. Four‐level systems
Authors: Bagrov V.G. , Baldiotti M.C. , Gitman D.M. , Levin A.D.
Published: June 2022

In the present article, we consider the so‐called two‐spin equation that describes four‐level quantum systems. Recently, these systems attract attention due to their relation to the problem of quantum computation. We study general properties of the two‐spin equation and show that the problem for certain external backgrounds can be identified with the problem of one spin in an appropriate background. This allows one to generate a number of exact solutions for two‐spin equations on the basis of already known exact solutions of the one‐spin equation. Besides, we present some exact solutions for the two‐spin equation with an external background different for each spin but having the same direction. We study the eigenvalue problem for a time‐independent spin interaction and a time‐independent external background. A possible analogue of the Rabi problem for the two‐spin equation is defined. We present its exact solution and demonstrate the existence of magnetic resonances in two specific frequencies, one of them coinciding with the Rabi frequency, and the other depending on the rotating field magnitude. The resonance that corresponds to the second frequency is suppressed with respect to the first one.
On the waves of plastic flow localization in pure metals and alloys
Authors: Zuev L.B.
Published: June 2022

The emergence in the deforming material of local strain patterns (self excited waves), which are ordered in space and evolve with time, has been investigated for a wide range of metals and alloys. The main parameters of these waves, i.e. propagation rate against work hardening coefficient, dispersion law and wavelength against specimen length and grain size, have been defined. The possibility of treating plastic flow localization as a process of plastic flow occurring in a deforming medium is considered. A set of equations has been developed, which is appropriate for the description of the evolution of local strain domains. The changes in the type of local strain pattern observed in the various stages of flow are examined. A model is proposed to account for the large‐scale periodicities exhibited by the distribution of localized deformation.
Equilibration of a dissipative quantum oscillator
Authors: Ambegaokar V.
Published: June 2022

An explicit demonstration is given of a harmonic oscillator in equilibrium approaching the equilibrium of a corresponding interacting system by coupling it to a thermal bath consisting of a continuum of harmonic oscillators.
Near field in quantum electrodynamics: Green functions, Lorentz condition, “nonlocality in the small”, frustrated total reflection
Authors: Perel'man M.E.
Published: June 2022

Investigation of near field in QED requires the refuse from an averaging of the Lorentz condition that smooths out some field peculiarities. Instead of it the Schwinger decomposition of 4‐potential with the Bogoliubov method of interaction switching in time and in space regions is considered. At such approach near field is describable by the part of covariant Green function of QED, the fast‐damping Schwinger function is formed by longitudinal and scalar components of Aμ none restricted by light cone. This description reveals possibility of superluminal phenomena within the near field zone as a “nonlocality in the small”. Some specification of the Bogoliubov method allows, as examples, descriptions of near fields of point‐like charge and at FTIR phenomena. Precisely such possibilities of nonlocal interactions are revealed in the common QED expressions for the Van‐der‐Waals and Casimir interactions and in the Förster law.
Local field contribution to the optical properties of multilevel coherent atomic media
Authors: Shen J.Q. , He S.
Published: June 2022

The local field contribution to some three‐ and four‐level coherent atomic vapors is considered, and a significant modification to optical properties due to dipole‐dipole interaction between neighboring atoms is discussed. It is found that the local field effect can reduce loss of a four‐level N‐type vapor medium at the resonant frequency in both the steady and transient cases. In order to achieve a left‐handed medium with a negative refractive index, a scenario to realize simultaneously negative permittivity and permeability inside a mixed coherent atomic vapor by using quantum coherence effect is suggested. One of the remarkable features of the present scheme is such that it can lead to a controllable manipulation of negative refractive index of an atomic vapor by using external coupling and signal fields. This may be a new scheme to fabricate the negatively refracting materials based on quantum optical approach.
Solutions of the Häussler‐von der Malsburg equations in manifolds with constant curvatures*
Authors: Güßmann M. , Pelster A. , Wunner G.
Published: June 2022

We apply generic order parameter equations for the emergence of retinotopy between manifolds of different geometry to one‐ and two‐dimensional Euclidean and spherical manifolds. To this end we elaborate both a linear and a nonlinear synergetic analysis which results in order parameter equations for the dynamics of connection weights between two cell sheets. Our results for strings are analogous to those for discrete linear chains obtained previously by Häussler and von der Malsburg. The case of planes turns out to be more involved as the two dimensions do not decouple in a trivial way. However, superimposing two modes under suitable conditions provides a state with a pronounced retinotopic character. In the case of spherical manifolds we show that the order parameter equations provide stable stationary solutions which correspond to retinotopic modes. A further analysis of higher modes furnishes proof that our model describes the emergence of a perfect one‐to‐one retinotopy between two spheres.
Duality between constraints and gauge conditions
Authors: Stoilov M.N.
Published: June 2022

There are two important sets of seemingly absolutely different objects in any gauge theory: the set of constraints, which generate the local symmetry and the set of gauge conditions, which fix this symmetry; the first one is determined by the Lagrangean of the model, the second is a matter of choice. However, in the transition amplitude constraints and gauge conditions participate in exactly the same way. This suggests the possibility for existence of a model with the same transition amplitude and in which gauge conditions and constraints are interchanged. We investigate the conditions that gauge fixing terms should satisfy so that this dual picture is allowed. En route, we propose to add new terms in the constraints which would generate the gauge transformation of the Lagrange multipliers and construct two BRST charges – one, as usual, for the constraints, and one for the gauge conditions.
A variable order constitutive relation for viscoelasticity
Authors: Ramirez L.E.S. , Coimbra C.F.M.
Published: June 2022

A constitutive relation for linear viscoelasticity of composite materials is formulated using the novel concept of Variable Order (VO) differintegrals. In the model proposed in this work, the order of the derivative is allowed to be a function of the independent variable (time), rather than a constant of arbitrary order. We generalize previous works that used fractional derivatives for the stress and strain relationship by allowing a continuous spectrum of non‐integer dynamics to describe the physical problem. Starting with the assumption that the order of the derivative is a measure of the rate of change of disorder within the material, we develop a statistical mechanical model that is in agreement with experimental results for strain rates varying more than eight orders of magnitude in value. We use experimental data for an epoxy resin and a carbon/epoxy composite undergoing constant compression rates in order to derive a VO constitutive equation that accurately models the linear viscoelastic deformation in time. The resulting dimensionless constitutive equation agrees well with all the normalized data while using a much smaller number of empirical coefficients when compared to available models in the literature.
The Z′ reconsidered
Authors: Ferroglia A. , Lorca A. , van der Bij J.J.
Published: June 2022

We consider the extension of the standard model with an arbitrary number of U(1) gauge fields coupled to baryon‐minus‐lepton number and/or hypercharge. Under the assumption that Abfb from the LEP1 experiment is an unlucky fluctuation, we find a mild indication for the presence of such fields in the precision electroweak data. A relatively large range of the Higgs boson mass is allowed. However we point out that the above assumption is controversial and not generally accepted in the community. We discuss the phenomenology of the extra U(1) fields.
Mapping electron delocalization by charge transport spectroscopy in an artificial molecule*
Authors: Gräber M.R. , Weiss M. , Keller D. , Oberholzer S. , Schönenberger C.
Published: June 2022

In this letter we present an experimental realization of the quantum mechanics textbook example of two interacting electronic quantum states that hybridize forming a molecular state. In our particular realization, the quantum states themselves are fabricated as quantum dots in a molecule, a carbon nanotube. For sufficient quantum‐mechanical interaction (tunnel coupling) between the two quantum states, the molecular wavefunction is a superposition of the two isolated (dot) wavefunctions. As a result, the electron becomes delocalized and a covalent bond forms. In this work, we show that electrical transport can be used as a sensitive probe to measure the relative weight of the two components in the superposition state as a function of the gate‐voltages. For the field of carbon nanotube double quantum dots, the findings represent an additional step towards the engineering of quantum states.
Counting statistics for the Anderson impurity model: Bethe ansatz and Fermi liquid study*
Authors: Gogolin A.O. , Konik R.M. , Ludwig A.W.W. , Saleur H.
Published: June 2022

We study the counting statistics of charge transport in the Anderson impurity model (AIM) employing both Keldysh perturbation theory in a Fermi liquid picture and the Bethe ansatz. In the Fermi liquid approach, the object of our principal interest is the generating function for the cumulants of the charge current distribution. We derive an exact analytic formula relating the full counting statistic (FCS) generating function to the self‐energy of the system in the presence of a measuring field. We first check that our approach reproduces correctly known results in simple limits, like the FCS of the resonant level system (AIM without Coulomb interaction). We then proceed to study the FCS for the AIM perturbatively in the Coulomb interaction. By comparing this perturbative analysis with a strong coupling expansion, we arrive at a conjecture for an expression for the FCS generating function at 𝒪(V3) (V is the voltage across the impurity) valid at all orders in the interaction. In the second part of the article, we examine a Bethe ansatz analysis of the current noise for the AIM. Unlike the Fermi liquid approach, here the goal is to obtain qualitative, not quantitative, results for a wider range of voltages both in and out of a magnetic field. Particularly notable are finite field results showing a double peaked structure in the current noise for voltages satisfying eV ∼ μB H. This double peaked structure is the “smoking gun” of Kondo physics in the current noise and is directly analogous to the single peak structure predicted in the differential conductance of the AIM.
Josephson junctions as detectors for non‐Gaussian noise*
Authors: Huard B. , Pothier H. , Birge N.O. , Esteve D. , Waintal X. , Ankerhold J.
Published: June 2022

Non‐Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on‐chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased effective temperature, but also the noise asymmetry. A theoretical description of the thermal escape of a Josephson junction in presence of noise with a non‐zero third cumulant is presented, together with numerical simulations when the noise source is a tunnel junction with Poisson noise. Comparison between experiment and theory is discussed.
Interference of independently emitted electrons in quantum shot noise*
Authors: Büttiker M. , Samuelsson P.
Published: June 2022

Theory predicts that electrons emitted from independent electron sources (metallic contacts) can nevertheless interfere. This interference is manifest in an exchange contribution to the shot noise correlation of currents at different contacts of a mesoscopic conductor. A geometry has been proposed in which second order (single particle) interference due to superposition of amplitudes is absent but fourth order (two‐particle) interference exhibits Aharonov‐Bohm oscillations. Recently such a geometry has been realized in an experiment and the theoretically predicted two‐particle Aharonov‐Bohm effect has been detected. We discuss Bell measurements and quantum state tomography using shot noise correlations. We discuss in addition structures in which two‐particle interference effects are generated dynamically by varying electrostatic potentials with the help of gates or by generating electron‐hole pairs by irradiating contacts of a mesoscopic conductor. These examples emphasize that two‐particle processes are not related to a particular geometry but are a general feature of multiparticle observables like shot noise correlations.
Circuit‐QED: How strong can the coupling between a Josephson junction atom and a transmission line resonator be?*
Authors: Devoret M.H. , Girvin Steven , Schoelkopf Robert
Published: June 2022

After reviewing the limitation by the fine structure constant α of the dimensionless coupling constant of an hydrogenic atom with a mode of the electromagnetic field in a cavity, we show that the situation presents itself differently for an artificial Josephson atom coupled to a transmission line resonator. Whereas the coupling constant for the case where such an atom is placed inside the dielectric of the resonator is proportional to α1/2, the coupling of the Josephson atom when it is placed in series with the conducting elements of the resonator is proportional to α‐1/2 and can reach values greater than 1.