Photon propagation in noncommutative QED with constant external field

view Abstract Citations (753) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Does the missing mass problem signal the breakdown of Newtonian gravity? Bekenstein, J. ; Milgrom, M. Abstract A nonrelativistic potential theory for gravity is considered which differs from the Newtonian theory. The theory is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass. The theory involves a modification of the Poisson equation and can be derived from a Lagrangian. The total momentum, angular momentum, and (properly defined) energy of an isolated system are conserved. The center-of-mass acceleration of an arbitrary bound system in a constant external gravitational field is independent of any property of the system. In other words, all isolated objects fall in exactly the same way in a constant external gravitational field (the weak equivalence principle is satisfied). However, the internal dynamics of a system in a constant external field is different from that of the same system in the absence of the external field, in violation of the strong principle of equivalence. These two results are consistent with the phenomenological requirements of the modified dynamics. A toy relativistic theory is sketched which has a nonrelativistic limit satisfying the requirements of the modified dynamics. Publication: The Astrophysical Journal Pub Date: November 1984 DOI: 10.1086/162570 Bibcode: 1984ApJ...286....7B Keywords: Galactic Rotation; Gravitation Theory; Mass Distribution; Missing Mass (Astrophysics); Newton Theory; Nonrelativistic Mechanics; Potential Theory; Computational Astrophysics; Cosmology; Equivalence; Poisson Equation; Astrophysics full text sources ADS |

Pair production in a constant electric field is closely analogous to bubble nucleation in a false vacuum. The classical trajectories of the pairs are Lorentz invariant, but it appears that this invariance should be broken by the nucleation process. Here, we use a model detector, consisting of other particles interacting with the pairs, to investigate how pair production is seen by different Lorentzian observers. We focus on the idealized situation where a constant external electric field is present for an infinitely long time, and we consider the in-vacuum state for a charged scalar field that describes the nucleating pairs. The in-vacuum is defined in terms of modes which are positive frequency in the remote past. Even though the construction uses a particular reference frame and a gauge where the vector potential is time dependent, we show explicitly that the resulting quantum state is Lorentz invariant. We then introduce a ``detector'' particle which interacts with the nucleated pairs, and show that all Lorentzian observers will see the particles and antiparticles nucleating preferentially at rest in the detector's rest frame. Similar conclusions are expected to apply to bubble nucleation in a sufficiently long lived vacuum. We also comment on certain unphysical aspects of the Lorentz invariant in-vacuum, associated with the fact that it contains an infinite density of particles. This can be easily remedied by considering Lorentz breaking initial conditions.

The exact solution for the chiral field superpropagator in a constant external Abelian field is given.

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

The effect of homogeneous and constant external electric fields on the structural stability of chignolin, a typical β-hairpin peptide, has been studied for 10ns using molecular dynamics simulations. The peptide aligns quickly its total dipole moment with the external electric field and then a constant stress is applied on its charged residues. For weaker fields this has mixed effects on the creation, destruction or strength of hydrogen bonds, but ultimately for strong fields chignolin unfolds starting by the separation of the terminal residues. Since the function of proteins is critically linked to their three-dimensional structures, these findings indicate that exposure to external electric fields may induce changes in conformation that can potentially initiate severe cellular dysfunction.

Pair production of open strings — relativistic versus dissipative dynamics

The MHD equations are integrated numerically for a homogeneous plasma initially at rest near a null line in a hyperbolic magnetic field. The finite plasma conductivity is taken into account. A solution of the linearized equations far from the null line — a cylindrical potential-perturbation wave converging on the null line - is adopted as a boundary condition. This perturbation arises when a constant external electric field is applied parallel to the null line. As the null line is approached, the wave becomes nonlinear and leads to the appearance of a thin current sheet. There is no evidence of any kind for the system of slow-mode shockwaves corresponding to the Petschek model. Within the current sheet the plasma density increases, while the density just outside the sheet decreases. The plasma flows along the sheet at approximately the Alfven velocity. A return current flows at the edges of the sheet.

This work explores the conditions that allow the injection and pinning of different magnetic domain walls (DWs) in Permalloy nanostripes with notches of different shapes. The injection is done under a constant external field by applying a 10 ns current pulse through an adjacent current line. The type of DW is identified by its anisotropic magnetoresistance (AMR). We find that, while a quasi-static pinning (nucleating at zero field and propagating the DW to the notch by slowly increasing the external field) would allow to distinguish different types of DWs pinned at the notch, a dynamic pinning (nucleating, propagating, and pinning the DW under a constant non-zero magnetic field) makes the discrimination of different DWs very difficult. Micromagnetic simulations indicate that the AMR of the different types of DWs become quite similar to each other as the injection field increases. This might explain why at large injection fields, usually only one or two values of resistance are detected, depending on the shape of the notch. Therefore, caution should be taken when establishing a one-to-one relationship between a type of DW and a value of resistance, especially if the injection is done under a non-zero external magnetic field.

Vacuum bubbles nucleate at rest with a certain critical size and subsequently expand. But what selects the rest frame of nucleation? This question has been recently addressed in [1] in the context of Schwinger pair production in 1+1 dimensions, by using a model detector in order to probe the nucleated pairs. The analysis in [1] showed that, for a constant external electric field, the adiabatic ``in" vacuum of charged particles is Lorentz invariant, {and in this} case pairs tend to nucleate preferentially at rest with respect to the detector. Here, we sharpen this picture by showing that the typical relative velocity between the frame of nucleation and that of the detector is at most of order Δv ∼ SE−1/3 << 1. Here, SE >> 1 is the action of the instanton describing pair creation. The bound Δv coincides with the minimum uncertainty in the velocity of a non-relativistic charged particle embedded in a constant electric field. A velocity of order Δv is reached after a time interval of order Δt ∼ SE−1/3r0 << r0 past the turning point in the semiclassical trajectory, where r0 is the size of the instanton. If the interaction takes place in the vicinity of the turning point, the semiclassical description of collision does not apply. Nonetheless, we find that even in this case there is still a strong asymmetry in the momentum transferred from the nucleated particles to the detector, in the direction of expansion after the turning point. We conclude that the correlation between the rest frame of nucleation and that of the detector is exceedingly sharp.

The spectrum of coupled ferroelectromagnetic waves in antiferroelectric antiferromagnets of arbitrary symmetry was found, taking into account the influence of external constant magnetic and electric fields. The diagram method was used to determine the contribution of magnon—magnon interaction to the free energy.

The phenomenology of the instability of charged and uncharged drops and liquid menisci at the end of a capillary through which liquid is fed in constant and variable external electric fields, both uniform and nonuniform, is considered. Methods of investigating such instability are described. The steady-state deformation of drops in electric fields, the critical conditions under which their charged surface loses stability, and the laws of electrical dispersion of liquids in the final stage of instability are discussed.

Quantum electrodynamics in an external constant field

Massive scalar and spin 1/2 fields are considered on a two-dimensional space-time with constant background curvature and in the presence of an external constant field. For each case, the Euler–Heisenberg effective action and the pair creation rate and their dependence on both the curvature and external field is determined exactly.

The effect of a pulsed (with a duration on the order of 1 ms) and of a constant external electric field on plasma-chemical processes in the lower ionosphere at altitudes of 70–100 km above the Earth’s surface is considered. Interest in these externally stimulated physical settings is associated with traditional radiophysical research and problems of radio-chemical atmospheric physics, which has been actively in recent years due to its various scientific and technical applications. A new page in this field of science (unlike the use of spurious radio signals) opens up the possibility of the purposeful field impact on a GPS receiver on the improvement of work and the further development of satellite navigation systems, which, undoubtedly, has not been discussed previously in the literature. In this work, on the basis of the numerical simulation, the concentrations of the main charged particles and the electron temperature in the presence of a strong external electric field have been calculated at an altitude of 100 km.

Within the QCD sum-rule approach in an external field, we calculate the baryon matrix element of isovector-scalar current, $H_{\rm B}=\langle B|\overline{u}u- \overline{d}d|B\rangle/2M_{\rm B}$, for octet baryons, which appears in the response of the correlator of baryon interpolating fields to a constant isovector-scalar external field. The sum rules are obtained for a general baryon interpolating field with an appropriate form for the phenomenological ansatz of the spectral density. The key phenomenological input is the response of the quark condensates to the external field. To first order in the quark mass difference $\delta m=m_d-m_u$, the non-electromagnetic part of the baryon isospin mass splitting is given by the product of $\delta m$ and $H_{\rm B}$. Therefore, QCD sum-rule calculation of $H_{\rm B}$ leads to an estimate of the octet baryon isospin mass splittings. The resulting values are comparable to the experimental values; however, the sum-rule predictions for $H_{\rm B}$ are sensitive to the values of the response of the quark condensates to the external source, which are not well determined.