bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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.
Is general relativity ‘essentially understood’? *
Authors: Friedrich H. 
Published: June 2022

AbstractThe 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

AbstractSome 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractIn 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

AbstractBy 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

AbstractInfrared 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

AbstractMore 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

AbstractWhen 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

AbstractThe 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

AbstractIt 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

AbstractThese 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).
The Einstein–Cartan–Elko system
Authors: Böhmer C.G. 
Published: June 2022

AbstractThe 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

AbstractThe 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

AbstractFollowing 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

AbstractIn 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

AbstractThe 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.
Near field in quantum electrodynamics: Green functions, Lorentz condition, “nonlocality in the small”, frustrated total reflection
Authors: Perel'man M.E. 
Published: June 2022

AbstractInvestigation 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

AbstractThe 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

AbstractWe 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

AbstractThere 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

AbstractA 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

AbstractWe 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.