Spin-one-half particles in strong electromagnetic fields: Spin effects and radiation reaction

Abstract

Various classical models of electrons including their spin degrees of freedom are commonly applied to describe the electron dynamics in strong electromagnetic fields. We demonstrate that different models can lead to different or even contradicting predictions regarding how the spin degree of freedom modifies the electron's orbital motion when the electron moves in strong electromagnetic fields. This discrepancy is rooted in the model-specific energy dependency of the spin-induced Stern-Gerlach force acting on the electron. The Frenkel model and the classical Foldy-Wouthuysen model are compared exemplarily in the nonrelativistic and the relativistic limits in order to identify parameter regimes where these classical models make different predictions. This allows for experimental tests of these models. In ultra strong laser setups in parameter regimes where effects of the Stern-Gerlach force become relevant, radiation-reaction effects are also expected to set in. We incorporate the radiation reaction classically via the Landau-Lifshitz equation and demonstrate that although radiation-reaction effects can have a significant effect on the electron trajectory, the Frenkel model and the classical Foldy-Wouthuysen model remain distinguishable also if radiation-reaction effects are taken into account. Our calculations are also suitable to verify the Landau-Lifshitz equation for the radiation reaction of electrons and other spin-1/2 particles.

Spin-dependent radiative deflection in the quantum radiation-reaction regime

“…The spin-dependent spectrum of an electron in (anti-)parallel state given by equation (3) is consistent the results from the well-known Sokolov-Ternov equation in equation (2). The radiation probability can also be classified to spin-flip case…”

“…Therefore it is a promising driver to trigger the spin effect on particle dynamics. Previous studies have shown that by colliding ∼10 1 MeV electrons with a laser of ∼10 22 W cm −2 , electrons with spin up/ down can be deflected to an angle of ±10 −7 rad by the SG force [2]. In the regime where SG effect emerges during collision, it is expected that other exotic phenomena become significant.…”

“…However, in a linearly-polarized (LP) laser pulse the electron spin projection onto the magnetic field axis in its rest frame oscillates with the laser field and the spin-induced net contribution is averaged to zero. Considering the SG effect being too weak as compared to the RR effect [2], present scenarios thus predict no sign of significant spin-dependent dynamics for LP laser fields with symmetric field distribution, except that asymmetry is introduced to the field itself in the few-cycle regime [12,13]. The new mechanism results from the coupling between the strong radiation reaction and spin effect, which is not active in the parameters investigated in [12] In this work, we show a new mechanism that leads to significant deflection of electrons by spin-induced effect in a symmetric LP laser field.…”

Life efficiency does not always increase with the dissipation rate

“…Near equilibrium the entropy production is just quadratic in the current, but that may change drastically farther from equilibrium. That appears again in recent studies of thermodynamic uncertainty relations [70][71][72][73][74][75], concentrating on lower bounds for the entropy production rate and giving interesting refinements to the positivity of entropy production or to Carnot efficiency, see [76] and references therein, in particular [40] for an interpretation of lower bounds on the dissipation rate. One should not forget that quadratic lower bounds for the dissipation rate, in terms of currents, are not at all sharp in the nonlinear force-current regimes.…”

Classical neutral point particle in linearly polarized EM plane wave field

“…Unfortunately, the generalization of relativistic quantum description for particles with anomalous magnetic moment is still not clear [17]. An overview of these approaches and their numerical tests can be found in [18,19]. Our model [1] expands on the pioneering work of the first formulations.…”