arXiv subjects

H. R. Reiss

Publications and source records attributed to H. R. Reiss.

14 recordsLinked to original sources

arXiv2022

Dual gauge concepts in electrodynamics, and new limitations on gauge invariance

Gauge invariance, a core principle in electrodynamics, has two separate meanings. One concept treats the photon as the gauge particle for electrodynamics. It is based on symmetries of the Lagrangian, and requires no mention of electric or magnetic fields. The second concept depends directly on the electric and magnetic fields, and how they can be represented by potential functions that are not unique. A general proof that potentials are more fundamental than fields serves to resolve discrepancies. Physical symmetries, however, are altered by gauge transformations and strongly limit gauge freedom. A new constraint on the form of allowable gauge transformations must be introduced that applies to both gauge concepts.

physics.gen-ph↗

arXiv2020

Fundamental formulation of electrodynamics revisited, and the precision of quantum electrodynamics

It was shown recently that unambiguous description of electromagnetic environments requires electromagnetic potentials; knowledge only of electric and magnetic fields is insufficient and can lead to error. Consequences of that demonstration are here applied to propagating fields, such as laser fields. Gauge invariance is replaced by symmetry preservation. This alteration makes it possible to understand how the known failure of the convergence of perturbation expansions in quantum electrodynamics (QED) follows from the fact that QED is incomplete; it does not contain its strong-field limit. Inherent in that demonstration are the strong-field coupling constant and the strong-field alteration of the mass shell of a charged particle. A variety of physically important consequences ensue, including the loss of guidance from Feynman diagrams. The meaning of tests for the precision of QED is questioned since such evaluations apply only to perturbative QED, but not to extensions required for complete QED.

physics.gen-ph↗

arXiv2019

Fundamental formulation of light-matter interactions revisited

The basic physics disciplines of Maxwell's electrodynamics and Newton's mechanics have been thoroughly tested in the laboratory, but they can nevertheless also support nonphysical solutions. The unphysical nature of some dynamical predictions is demonstrated by the violation of symmetry principles. Symmetries are fundamental in physics since they establish conservation principles. The procedures explored here involve gauge transformations that alter basic symmetries, and these alterations are possible because gauge transformations are not necessarily unitary despite the widespread assumption that they are. That gauge transformations can change the fundamental physical meaning of a problem despite the preservation of electric and magnetic fields is a universal proof that potentials are more basic than fields. These conclusions go to the heart of physics. Problems are not evident when fields are perturbatively weak, but the properties demonstrated here can be critical in strong-field physics where the electromagnetic potential becomes the dominant influence in interactions with matter.

physics.gen-ph↗

arXiv2019

Electrodynamics of the strong-field approximation and deficiencies of the tunneling model

The strong-field laser physics enterprise is investing important resources in the study of the effects of oscillatory electric fields on matter using the tunneling concept, whereas laser fields are vector fields that do not support the tunneling model. Oscillatory electric fields and propagating plane-wave laser fields are different electrodynamic phenomena, and similarities in their effects diminish as field intensity increases. Major differences are known in the case of very low frequencies where oscillatory electric fields act adiabatically as the frequency declines, in contrast to extreme relativistic effects of strong laser fields. Many supposed new phenomena, such as ATI (Above-Threshold Ionization), channel closing, and stabilization were studied in terms of propagating fields before they came to the attention of the atomic physics community. This illustrates the efficiency of using proper electrodynamic methods for the treatment of laser effects. Problems arising from the conflation of the effects of oscillatory electric fields and propagating fields are exacerbated by using ill-defined nomenclature, such as KFR and SFA, that has been used indiscriminately to apply both to oscillatory electric fields and to propagating fields. Research resources can be applied with much-improved efficiency if proper electrodynamic treatment of laser fields is employed.

physics.gen-ph↗

arXiv2018

Ascendancy of potentials over fields in electrodynamics

Multiple bases are presented for the conclusion that potentials are fundamental in electrodynamics, with electric and magnetic fields as quantities auxiliary to the scalar and vector potentials -- opposite to the conventional ordering. One foundation for the concept of basic potentials and auxiliary fields consists of examples where two sets of gauge-related fields are such that one is physical and the other is erroneous, with the information for the proper choice supplied by the potentials. A major consequence is that a change of gauge is not a unitary transformation in quantum mechanics; a principle heretofore unchallenged. The primacy of potentials over fields leads to the concept of a hierarchy of physical quantities, where potentials and energies are primary, while fields and forces are secondary. Secondary quantities provide less information than do primary quantities. Some criteria by which strong laser fields are judged are based on secondary quantities, making it possible to arrive at inappropriate conclusions. This is exemplified by several field-related misconceptions as diverse as the behavior of charged particles in very low frequency propagating fields, and the fundamental problem of pair production at very high intensities. In each case, an approach based on potentials gives appropriate results, free of ambiguities. The examples encompass classical and quantum phenomena, in relativistic and nonrelativistic conditions. This is a major extension of the quantum-only Aharonov-Bohm effect, both in supporting the primacy of potentials over fields, and also in showing how field-based conceptions can lead to errors in basic applications.

physics.gen-ph↗

arXiv2017

Laser fields and proxy fields

The convention in Atomic, Molecular, and Optical (AMO) physics of employing the dipole approximation to describe laser-induced processes replaces four source-free Maxwell equations governing laser fields with a single Maxwell equation for a "proxy" field that requires a virtual source current for its existence. Laser fields are transverse, but proxy fields are longitudinal; there can be no gauge equivalence. The proxy field is sometimes serviceable, but its limitations are severe. One example is the "above-threshold ionization" (ATI) phenomenon; surprising by proxy-field understanding, but natural and predicted in advance of observation with a laser-field method. An often-overlooked limitation is that numerical solution of the time-dependent Schrödinger equation (TDSE) is exact for proxy fields, but not for laser fields. Acceptance of proxy-field concepts has been costly in terms of inefficiently deployed research resources. Calculations with a nearly-40-year old transverse-field method remain unmatched with proxy fields. The transverse-field method is applicable in the "tunneling" domain, the "multiphoton" domain, and, as shown here, in the low-frequency "magnetic" domain. Attempts to introduce low-frequency magnetic field corrections into TDSE cannot be expected to produce meaningful results. They would be based on inappropriate Maxwell equations, a non-existent virtual source, and would approach constant electric field properties as the field frequency declines. Laser fields propagate at the speed of light for all frequencies; they cannot approach a constant-field limit. Extremely strong laser fields are unambiguously relativistic; a nonrelativistic limit that connects continuously to the relativistic domain is simpler conceptually and mathematically than is a theory constructed with a proxy field that is certain to fail as intensities increase.

physics.atom-ph↗

arXiv2017

Physical restrictions on the choice of electromagnetic gauge and their practical consequences

It is shown that electromagnetic potentials convey physical information beyond that supplied by electric and magnetic fields alone, and are thus more fundamental. Observable physical properties can impose conditions on the selection of electromagnetic gauge (i.e. sets of potentials) that are explicit and restrictive. This is true both classically and quantum mechanically. The implication that the choice of gauge carries physical information is confirmed by exhibiting a set of potentials that describes fields correctly, but that violates physical constraints. The basic conclusions are that physical requirements place limits on acceptable gauges; and that potentials are more fundamental than fields in both classical and quantum physics, representing a major generalization of the quantum-only Aharonov-Bohm effect. These important properties are obscured if the dipole approximation is employed. The properties demonstrated here relate directly to conditions that exist in strong-field laser applications.

quant-ph↗

arXiv2015

Strong limitations on allowable gauge transformations in electrodynamics

Conservation principles establish the primacy of potentials over fields in electrodynamics, both classical and quantum. The contrary conclusion that fields are primary is based on the Newtonian concept that forces completely determine dynamics, and electromagnetic forces depend directly on fields. However, physical conservation principles come from symmetries such as those following from Noether's theorem, and these require potentials for their statement. Examples are given of potentials that describe fields correctly but that violate conservation principles, demonstrating that the correct statement of potentials is necessary. An important consequence is that gauge transformations are severely limited when conservation conditions must be satisfied. When transverse and longitudinal fields are present concurrently, the only practical gauge is the radiation gauge.

physics.class-ph↗

arXiv2015

Low-frequency failure of the Göppert-Mayer gauge transformation and consequences for the Strong-Field Approximation

The Göppert-Mayer (GM) gauge transformation, of central importance in atomic, molecular, and optical physics since it connects the length gauge and the velocity gauge, becomes unphysical as the field frequency declines towards zero. This is not consequential for theories of transverse fields, but it is the underlying reason for the failure of gauge invariance in the dipole-approximation version of the Strong-Field Approximation (SFA). This failure of the GM gauge transformation explains why the length gauge is preferred in analytical approximation methods for fields that possess a constant electric field as a zero-frequency limit.

quant-ph↗

arXiv2014

The tunneling model of laser-induced ionization and its failure at low frequencies

The tunneling model of ionization applies only to longitudinal fields: quasistatic electric fields that do not propagate. Laser fields are transverse: plane wave fields that possess the ability to propagate. Although there is an approximate connection between the effects of longitudinal and transverse fields in a useful range of frequencies, that equivalence fails completely at very low frequencies. Insight into this breakdown is given by an examination of radiation pressure, which is a unique transverse-field effect whose relative importance increases rapidly as the frequency declines. Radiation pressure can be ascribed to photon momentum, which does not exist for longitudinal fields. Two major consequences are that the near-universal acceptance of a static electric field as the zero frequency limit of a laser field is not correct; and that the numerical solution of the dipole-approximate Schrödinger equation for laser effects is inapplicable as the frequency declines. These problems occur because the magnetic component of the laser field is very important at low frequencies, and hence the dipole approximation is not valid. Some experiments already exist that demonstrate the failure of tunneling concepts at low frequencies.

physics.atom-ph↗

arXiv2013

The mass shell of strong-field quantum electrodynamics

It has long been known that a free electron in an intense plane-wave field has a mass shell that differs from the usual free-electron mass shell, with a form that implies that an intensity-dependent increase in mass occurs. It has been an enticing, but elusive goal to observe this mass shift. Many schemes have been proposed by which a definitive measurement may be made, and some claims of success exist, but these tests are not conclusive. It is shown here that the intense-field mass shell is not the result of a change in mass. Rather, it is a consequence of the potential energy that a charged particle must possess in the presence of a plane-wave field. When the effects of this potential are incorporated in a properly covariant form, the mass shift no longer appears and kinematical relations are conventional. If the plane-wave pulse is sufficiently long to allow the electron to exit the field adiabatically, then there is no alteration at all of the mass shell expression. Other aspects of the role played by the ponderomotive 4-potential are examined. It is also shown that the putative "relativistic mass" of the electron is illusory when confronted with covariance requirements. Both "mass increases" of the electron are thereby discredited by fundamental principles.

quant-ph↗

arXiv2013

Altered Maxwell equations in the length gauge

The length gauge uses a scalar potential to describe a laser field, thus treating it as a longitudinal field rather than as a transverse field. This distinction is revealed in the fact that the Maxwell equations that relate to the length gauge are not the same as those for transverse fields. In particular, a source term is necessary in the length-gauge Maxwell equations, whereas the Coulomb-gauge description of plane waves possesses the basic property of transverse fields that they propagate with no source terms at all. This difference is shown to be importantly consequential in some previously unremarked circumstances; and it explains why the Göppert-Mayer gauge transformation does not provide the security that might be expected of full gauge equivalence.

physics.optics↗

arXiv2013

Incompatibility of the tunneling limit with laser fields

The Schwinger limit refers to longitudinal electric fields that are sufficiently strong to "polarize the vacuum" into electron-positron pairs by a tunneling mechanism. Laser fields are transverse electromagnetic fields for which the Schwinger limit has no relevance. Longitudinal and transverse fields are fundamentally different because of the different values of the F^{μν}F_{μν} Lorentz invariant that characterizes the fields. One aspect of this difference is the zero-frequency limit, that exists for longitudinal fields, but is ill-defined for transverse fields. The goal of approaching the Schwinger limit with sufficiently strong lasers is thus not a possibility. Tunneling transition rates are characterized by an exponential behavior of the form exp(-C/E), where E is the magnitude of the applied electric field and C is a system-dependent constant. Searches for such behavior within a Coulomb-gauge treatment of laser-induced processes are shown to fail.

quant-ph↗

arXiv2013

Limitations of gauge invariance

Although gauge invariance preserves the values of physical observables, a gauge transformation can introduce important alterations of physical interpretations. To understand this, it is first shown that a gauge transformation is not, in general, a unitary transformation. Also, physical interpretations are based on both kinetic energy and potential energy expressions. While the kinetic energy is a measurable quantity, and hence gauge-invariant, the potential energy is gauge-dependent. Two basic examples are examined; one classical and the other quantum-mechanical. The aim is to show that the use of the Coulomb (or radiation) gauge is always consistent with the way that fields are generated in the laboratory. Upon transformation out of the Coulomb gauge, this connection is lost, and physical interpretations can give rise to misleading inferences.

quant-ph↗