On Existence of Ground States in the Spin Boson Model

We show the existence of ground states in the massless spin boson model without any infrared regularization. Our proof is non-perturbative and relies on a compactness argument. It works for arbitrary values of the coupling constant under the hypothesis that the second derivative of the ground state energy as a function of a constant external magnetic field is bounded.

Fluctuation Relations for Dissipative Systems in Constant External Magnetic Field: Theory and Molecular Dynamics Simulations

We illustrate how, contrary to common belief, transient Fluctuation Relations (FRs) for systems in constant external magnetic field hold without the inversion of the field. Building on previous work providing generalized time-reversal symmetries for systems in parallel external magnetic and electric fields, we observe that the standard proof of these important nonequilibrium properties can be fully reinstated in the presence of net dissipation. This generalizes recent results for the FRs in orthogonal fields—an interesting but less commonly investigated geometry—and enables direct comparison with existing literature. We also present for the first time a numerical demonstration of the validity of the transient FRs with nonzero magnetic field via nonequilibrium molecular dynamics simulations of a realistic model of liquid NaCl.

Mean-field BCS theory of the Meissner effect in bulk revisited

We show that the implementation of the $$1/ c^2 $$ 1 / c 2 transverse current–current interaction between electrons resulting from the non-relativistic QED into the standard self-consistent electron BCS model in bulk under thermal equilibrium in the stable superconductive phase ensures the full compensation of a constant external magnetic field by the internal magnetic field created by the electrons, i.e. one has an ideal diamagnet. GraphicAbstract

Mean-field Theory of the Meissner Effect in Bulk Revisited

We show that the implementation of the 1/c² transverse current-current interaction between electrons into the standard self-consistent electron BCS model in bulk under thermal equilibrium ensures in the stable superconductive phase the full compensation of a constant external magnetic field by the internal magnetic field created by the electrons i.e. one has an ideal diamagnet. However, no proof of the phenomenological London equation emerges within the bulk approach.

Mean-Field Theory of the Meissner effect in Bulk Revisited

We show that the implementation of the 1/c² transverse current-current interaction between elec- trons into the standard self-consistent electron BCS model in bulk under thermal equilibrium in the stable superconductive phase ensures the full compensation of a constant external magnetic field by the internal magnetic field created by the electrons.

A Novel Augmented Railgun Using Permanent Magnets

A novel augmented railgun using a permanent magnet is proposed in this paper. The effects of the permanent magnet on the magnetic field and distribution of current density have been investigated. High current densities in the railguns can lead to high local temperature and erosion of the rails. Therefore, the current densities in the rails and armature should be decreased without the reduction of the Lorentz force which is required for acceleration. For this purpose, augmentation of the magnetic field can be used as an effective method. The Finite Element Method (FEM) simulations have been applied in this article to analyze the performance of the railgun in the presence of the magnets. Two augmented railgun structures have been introduced to produce a constant external magnetic field. For both structures, augmented railgun characteristics are studied in comparison to the railgun without the augmentation. The results show that augmentation with permanent magnet increases railgun efficiency, especially in low current railguns. For pulse current source I=30kA, Lorentz force of the augmented railgun with four magnets is 2.02 times greater than the conventional railgun.

Vacuum Birefringence in a Supercritical Magnetic Field

The birefringence effect in vacuum in strong magnetic fields has been considered. The polarization tensor in a constant external magnetic field is analyzed in the framework of quantum field theory and on the basis of the electron Green’s function calculated as the sum over the Landau levels. The case of the lowest Landau levels for photons with the energies below the electron-positron pair creation threshold is considered, and the corresponding refractive indices of the physical vacuum for anomalous and normal waves are determined.

1-Loop mass generation by a constant external magnetic field for an electron propagating in a thin medium

The 1-loop self-energy of a Dirac electron of mass [Formula: see text] propagating in a thin medium simulating graphene in an external magnetic field [Formula: see text] is investigated in quantum field theory. Equivalence is shown with the so-called reduced QED[Formula: see text] on a 2-brane. Schwinger-like methods are used to calculate the self-mass [Formula: see text] of the electron when it lies in the lowest Landau level. Unlike in standard QED[Formula: see text], it does not vanish at the limit [Formula: see text]: [Formula: see text] on-mass-shell renormalization conditions (with [Formula: see text]); all Landau levels of the virtual electron are taken into account and are implemented. Restricting to the sole lowest Landau level of the virtual electron is explicitly shown to be inadequate. Resummations at higher orders lie beyond the scope of this work.