A. E. Lobanov

On classical description of radiation from neutral fermion with anomalous magnetic moment

Abstract Electromagnetic radiation from an uncharged spin 1/2 particle with an anomalous magnetic moment moving in the classical electromagnetic external field originates from quantum spin-flip transitions. Although this process has a purely quantum nature, it was observed for certain particular external field configurations that, when quantum recoil is neglected, the radiation power corresponds to the classical radiation from an evolving magnetic dipole. We argue that this correspondence has a more general validity in the case of an unpolarized particle and derive a general formula for radiation in terms of the external field strength and its derivative. A classical dynamics of the spin is described by the Bargmann–Michel–Telegdi equation.

Solutions of the classical equation of motion for a spin in electromagnetic fields

The evolution of a charged particle spin in electromagnetic fields of a special form is investigated based on the Bargmann-Michel-Telegdi equation. For some types of nonhomogeneous fields, an exact analytic form of the dependence of the spin vector on the four-dimensional velocity of the particle is found.

Oscillations of particles in the Standard Model

We construct Hilbert spaces of particle states such that all neutrinos and also charged leptons and up and down quarks are united into multiplets and their components can be treated as different quantum states of a single particle. The phenomenon of neutrino oscillations arises in a theory based on the Lagrangian of the fermionic sector of the Standard Model modified according to the proposed approach.

Neutrino Oscillations in Dense Matter

A modification of the electroweak theory, where the fermions with the same electroweak quantum numbers are combined in multiplets and are treated as different quantum states of a single particle, is proposed. In this model, mixing and oscillations of particles arise as a direct consequence of the general principles of quantum field theory. The developed approach enables one to calculate the probabilities of the processes taking place in the detector at long distances from the particle source. Calculations of higher-order processes, including computation of the contributions due to radiative corrections, can be performed in the framework of the perturbation theory using the regular diagram technique. As a result, the analog to the Dirac–Schwinger equation of quantum electrodynamics describing neutrino oscillations and its spin rotation in dense matter can be obtained.

Dynamics of a Dirac particle in the theory with Lorentz invariance violation

Solutions to the Dirac equations have been obtained for particles interacting with vector, axial-vector, and tensor condensates within the framework of the Standard Model Extension. Possible applications of these solutions for describing the neutrino behavior in dense matter and electromagnetic field are considered.

Nuclear β decay with massive neutrino in an external electromagnetic field

beta decay in the presence of an external electromagnetic field is investigated, taking into account the non-zero neutrino rest mass. The spectrum of electrons and polarisation effects of different orientations of nuclear spin are considered. It is shown that the electromagnetic wave substantially modifies the boundaries of the spectrum of beta electrons. The results, which include an analysis of the total decay probability in intense magnetic fields, may have various astrophysical implications.

Dynamics of electron spin in undulators

The problem on the evolution of electron spin in inhomogeneous magnetic fields of special type is solved on the basis of the classical Bargmann-Michel-Telegdi equation. The results obtained are used to analyze the behavior of electron spin in magnetic undulators.

Investigating the effect of a magnetic field on beta decay

The effect of an external magnetic field on theβ-decay process of a neutron is analyzed in detail. The spin effects within this process are studied, as is the final mass of the neutrino. Results of computer-based experiments are presented.

Neutrino oscillations in a homogeneous moving medium

The quasi-classical equation that describes both neutrino flavor oscillations and spin rotation in dense matter is obtained in the framework of quantum field theory. The solution of this equation for homogeneous medium is found. The probabilities of the spin-flavor transitions in unpolarized moving matter are calculated in the two-flavor model. We show that if the medium is at rest the neutrino helicity is conserved and the flavor transition probabilities are equal to those obtained using the phenomenological approach.

Operators of observables for a neutral particle with anomalous magnetic moment in an electromagnetic field

The explicit form of operators of kinetic momenta and spin projection for a neutral particle with an anomalous magnetic moment in constant homogeneous electromagnetic field is found. The possible applications of the obtained results in neutrino physics are considered.