Monopôle magnétique

Résumé

Un monopôle magnétique est une particule hypothétique qui porterait une masse (ou charge) magnétique ponctuelle, au contraire des aimants habituels qui possèdent deux pôles magnétiques opposés. Histoire L'existence de monopôles magnétiques est exclue par l'électromagnétisme classique et par la théorie de la relativité, mais en 1931 Paul Dirac en a démontré l'existence théorique dans le cadre de la physique quantique. En septembre 2009, des chercheurs ont observé des quasiparticules artificielles présentant les propriétés du monopôle magnétique. Mais à ce jour, aucune particule élémentaire "libre" disposant d'un monopôle magnétique n'a été observée. Si une particule élémentaire disposant d'un monopôle magnétique était observée, les conséquences seraient importantes au niveau des théories d'unification des lois fondamentales de la physique car ces dernières s'opposent sur ce point. Point de vue des équations de Maxwell La dissymétrie expérimentale des équatio

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https://fr.wikipedia.org/wiki/Monop%C3%B4le_magn%C3%A9tique

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We interpret the recent NANOGrav results in terms of a stochastic gravitational wave background from metastable cosmic strings. The observed amplitude of a stochastic signal can be translated into a range for the cosmic string tension and the mass of magnetic monopoles arising in theories of grand unification. In a sizable part of the parameter space, this interpretation predicts a large stochastic gravitational wave signal in the frequency band of ground-based interferometers, which can be probed in the very near future. We confront these results with predictions from successful inflation, leptogenesis and dark matter from the spontaneous breaking of a gauged B - L symmetry. (C) 2020 The Authors. Published by Elsevier B.V.

2020

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Estimation of Charge Transfer During Long Continuing Currents in Natural Downward Flashes Using Single‐Station E‐Field Measurements

Hannes Kohlmann

The amount of charge transferred to ground during long continuing currents in natural downward flashes can be obtained either through direct current measurements or using remote electromagnetic fields, if direct measurements are not feasible. In this study, measurements of a single-station E-field antenna were used to estimate charge transfer during continuing currents. With time-synchronized high-speed video recordings serving as ground-truth data for continuing current occurrence, we estimate transferred charge during long continuing currents in 140 natural downward flashes from electric field changes, assuming a simple monopole charge model. We present average parameters for the duration, transferred charge, amplitude, and the average amplitude on five segments along the channel. Further, we perform a simulation to investigate the estimation performance of the monopole charge model, when the cloud charge is spatially extended. Using an extended charge distribution model, we generate single-station remote field waveforms and infer the charge with the monopole model. Comparison of the known and inferred charge yields estimation errors depending on the leader orientation, its spatial extension, and the observation distance. A Monte Carlo approach is carried out to statistically evaluate parameter deviations. This novel estimation error analysis sheds light on the limitations of the applied simple techniques for charge transfer estimation of long continuing currents using single-station electric field measurements.

2022

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A metastable cosmic-string network is a generic consequence of many grand unified theories (GUTs) when combined with cosmic inflation. Metastable cosmic strings are not topologically stable, but decay on cosmic time scales due to pair production of GUT monopoles. This leads to a network consisting of metastable long strings on superhorizon scales as well as of string loops and segments on subhorizon scales. We compute for the first time the complete stochastic gravitational-wave background (SGWB) arising from all these network constituents, including several technical improvements to both the derivation of the loop and segment contributions. We find that the gravitational waves emitted by string loops provide the main contribution to the gravitational-wave spectrum in the relevant parameter space. The resulting spectrum is consistent with the tentative signal observed by the NANOGrav and Parkes pulsar timing collaborations for a string tension of G mu similar to 10(-11...-7) and has ample discovery space for ground- and space-based detectors. For GUT-scale string tensions, G mu similar to 10(-8...-7), metastable strings predict a SGWB in the LIGO-Virgo-KAGRA band that could be discovered in the near future.

IOP Publishing Ltd2021

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