Particule de Dirac

On appelle particule de Dirac toute particule de type fermion dont l'antiparticule est différente. C'est le cas de toute particule chargée (un électron et son positron par exemple). Elles sont nommées ainsi en raison de la mise en évidence par Paul Dirac en 1928 de l'existence du positron. Les particules de Majorana D'autres particules de charge nulle (telles les neutrinos) seraient en revanche susceptibles d'être leur propre antiparticule : il s'agirait alors de particules dites de Majorana, dont l'existence n'a toujours pas été confirmée à mi-2016. Voir aussi

Mécanique quantique relativiste
Équation de Dirac
Isolant topologique

Liens externes

Banque des Savoirs : La théorie du neutrino de Majorana

Equation de Dirac Equation de Dirac Equation de Dirac

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PHYS-431: Quantum field theory I

The goal of the course is to introduce relativistic quantum field theory as the conceptual and mathematical framework describing fundamental interactions.

PHYS-415: Particle physics I

Presentation of particle properties, their symmetries and interactions. Introduction to quantum electrodynamics and to the Feynman rules.

Polarization of photons emitted by decaying dark matter

Anna Tokareva

Radiatively decaying dark matter may be searched through investigating the photon spectrum of galaxies and galaxy clusters. We explore whether the properties of dark matter can be constrained through the study of a polarization state of emitted photons. Starting from the basic principles of quantum mechanics we show that the models of symmetric dark matter are indiscernible by the photon polarization. However, we find that the asymmetric dark matter consisted of Dirac fermions is a source of circularly polarized photons, calling for the experimental determination of the photon state. (C) 2016 The Authors. Published by Elsevier B.V.

Elsevier2017

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An on/off Berry phase switch in circular graphene resonators

Donat Fabian Natterer, Yue Zhao

The phase of a quantum state may not return to its original value after the system's parameters cycle around a closed path; instead, the wave function may acquire a measurable phase difference called the Berry phase. Berry phases typically have been accessed through interference experiments. Here, we demonstrate an unusual Berry phase-induced spectroscopic feature: a sudden and large increase in the energy of angular-momentum states in circular graphene p-n junction resonators when a relatively small critical magnetic field is reached. This behavior results from turning on a p Berry phase associated with the topological properties of Dirac fermions in graphene. The Berry phase can be switched on and off with small magnetic field changes on the order of 10 millitesla, potentially enabling a variety of optoelectronic graphene device applications.

American Association for the Advancement of Science2017

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Dirac vs. Majorana HNLs (and their oscillations) at SHiP

SHiP is a proposed high-intensity beam dump experiment set to operate at the CERN SPS. It is expected to have an unprecedented sensitivity to a variety of models containing feebly interacting particles, such as Heavy Neutral Leptons (HNLs). Two HNLs or more could successfully explain the observed neutrino masses through the seesaw mechanism. If, in addition, they are quasi-degenerate, they could be responsible for the baryon asymmetry of the Universe. Depending on their mass splitting, HNLs can have very different phenomenologies: they can behave as Majorana fermions - with lepton number violating (LNV) signatures, such as same-sign dilepton decays - or as Dirac fermions with only lepton number conserving (LNC) signatures. In this work, we quantitatively demonstrate that LNV processes can be distinguished from LNC ones at SHiP, using only the angular distribution of the HNL decay products. Accounting for spin correlations in the simulation and using boosted decision trees for discrimination, we show that SHiP will be able to distinguish Majorana-like and Dirac-like HNLs in a significant fraction of the currently unconstrained parameter space. If the mass splitting is of order 10(-6) eV, SHiP could even be capable of resolving HNL oscillations, thus providing a direct measurement of the mass splitting. This analysis highlights the potential of SHiP to not only search for feebly interacting particles, but also perform model selection.

2020

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Fermion

En physique des particules, un fermion (nom attribué par Paul Dirac d'après Enrico Fermi) est une particule de spin demi-entier (c'est-à-dire 1/2, 3/2, 5/2...). Elle obéit à la statistique de Fermi-

Neutrino

Le neutrino est une particule élémentaire du modèle standard de la physique des particules. Les neutrinos sont des fermions de , plus précisément des leptons. Ils sont électriquement neutres. Il en

Chirality (physics)

A chiral phenomenon is one that is not identical to its (see the article on mathematical chirality). The spin of a particle may be used to define a handedness, or helicity, for that particle, which,