Particle In Circular Motion Research Articles

Can a charged decaying particle serve as an ideal clock in the presence of a magnetic field?

We investigate a model of a supposedly ideal clock based on the decay rate of a charged particle in circular motion in a constant magnetic field. We show that the time measured by an ideal clock depends on the acceleration. However, the effect becomes visible at an order of magnitude of 10^{28} g, therefore confirming the validity of the ideal clock hyphotesis for realistic accelerations.

Spinning test body orbiting around a Kerr black hole: Circular dynamics and gravitational-wave fluxes

In a recent work, [Phys. Rev. D. 94, 104010 (2016)], hereafter Paper I, we have numerically studied different prescriptions for the dynamics of a spinning particle in circular motion around a Schwarzschild black hole. In the present work, we continue this line of investigation to the rotating Kerr black hole. We consider the Mathisson-Papapetrou formalism under three different spin-supplementary-conditions (SSC), the Tulczyjew SSC, the Pirani SSC and the Ohashi-Kyrian-Semerak SSC, and analyze the different circular dynamics in terms of the ISCO shifts and the frequency parameter ${x \equiv (M \Omega)^{2/3}}$, where $\Omega$ is the orbital frequency and $M$ is the Kerr black hole mass. Then, we solve numerically the inhomogeneous $(2+1)D$ Teukolsky equation to contrast the asymptotic gravitational wave fluxes for the three cases. Our central observation made in Paper I for the Schwarzschild limit is found to hold true for the Kerr background: the three SSCs reduce to the same circular dynamics and the same radiation fluxes for small frequency parameters but differences arise as $x$ grows close to the ISCO. For a positive Kerr parameter $a=0.9$ the energy fluxes mutually agree with each other within a $0.2\%$ uncertainty up to $x<0.14$, while for $a=-0.9$ this level of agreement is preserved up to $x<0.1$. For large frequencies ($x \gtrsim 0.1$), however, the spin coupling of the Kerr black hole and the spinning body results in significant differences of the circular orbit parameters and the fluxes, especially for the $a=-0.9$ case. Instead, in the study of ISCO the negative Kerr parameter $a=-0.9$ results in less discrepancies in comparison with the positive Kerr parameter $a=0.9$.

Gravitational waves emitted by a particle rotating around a Schwarzschild black hole: A semiclassical approach

We analyze the gravitational radiation emitted from a particle in circular motion around a Schwarzschild black hole using the framework of quantum field theory in curved spacetime at tree level. The gravitational perturbations are written in a gauge-invariant formalism for spherically symmetric spacetimes. We discuss the results, comparing them to the radiation emitted by a particle when it is assumed to be orbiting a massive object due to a Newtonian force in flat spacetime.

Stopping power andpolarization induced in a plasma by a fast charged particle incircular motion

We describe the perturbation induced in a plasma by a charged particle incircular motion, analysing in detail the evolution of the induced charge,the electrostatic potential and the energy loss of the particle. We describethe initial transitory behaviour and the different ways in which convergenceto final stationary solutions may be obtained depending on the basicparameters of the problem. The results for the stopping power show aresonant behaviour which may give place to large stopping enhancement valuesas compared with the case of particles in straight-line motion with the samelinear velocity. The results also explain a resonant effect recentlyobtained for particles in circular motion in magnetized plasmas.

Gravitational radiation from a particle in circular orbit around a black hole. III. Stability of circular orbits under radiation reaction.

We use the Teukolsky perturbation formalism to show that (i) a particle in circular motion around a nonrotating black hole remains in a circular orbit under the influence of radiation reaction, and (ii) circular orbits are stable only if the orbital radius is greater than a critical radius ${\mathit{r}}_{\mathit{c}}$\ensuremath{\simeq}6.6792M, where M is the mass of the black hole. A circular orbit is stable if, when slightly perturbed so that it acquires a small eccentricity, the radiation reaction decreases the eccentricity; a circular orbit is unstable if the radiation reaction increases the eccentricity. Our analysis is restricted by four major assumptions: (i) the black hole is nonrotating, (ii) the eccentricity is always small, (iii) the gravitational perturbations are linear, and (iv) the adiabatic approximation (that the radiation reaction takes place over a time scale much larger than the orbital period) is valid. On the other hand, our analysis is not limited to weak-field, slow-motion situations; it is valid for particle motion in strong gravitational fields.

The influence of the magnetic field gradient on the position and the polarization of a polarized particle in circular motion

This paper gives an estimate of the classical motion for a charged spin-1/2 particle with an anomalous magnetic moment moving in a magnetic field by including the effect of the first-order field gradient.