arXiv subjects

Keita Seto

Publications and source records attributed to Keita Seto.

8 recordsLinked to original sources

arXiv2025

Coherent-field QED transitions based on coherent-state boundary conditions

We develop a coherent-field formulation of quantum electrodynamics (QED) based on coherent-state boundary conditions, in which laser fields are represented by asymptotic coherent states rather than by prescribed classical background fields. Starting from coherent-state boundary conditions and the displacement-operator formalism, we construct operator and path-integral descriptions of transitions between distinct electromagnetic coherent states. This formulation provides a coherent-field extension of conventional background-field QED and incorporates the quantum dynamics of the coherent field itself. The corresponding path-integral representation contains a functional integral over coherent-field histories in addition to the usual functional integral over quantum fluctuations, thereby extending the conventional background-field description. The resulting path-integral representation naturally leads to an effective action for the stationary coherent-field configuration. The corresponding saddle-point condition yields an effective Maxwell equation containing contributions from vacuum polarization, photon fluctuations, and coherent-field fluctuations. In the limit where the latter two contributions vanish, the formalism reduces to the conventional Heisenberg-Euler description.

physics.plasm-ph↗

arXiv2021

Radiation Reaction of Betatron Oscillation in Plasma Wakefield Accelerators

A classical model of radiation reaction for the betatron oscillation of an electron in a plasma wakefield accelerator is presented. The maximum energy of the electron due to the longitudinal radiation reaction is found, and the betatron oscillation damping due to both the longitudinal and transverse radiation reaction effects is analyzed. Both theoretical and numerical solutions are shown with good agreements. The regime that the quantum radiation takes effect is also discussed. This model is important for designing future plasma based super accelerators or colliders.

physics.plasm-ph↗

arXiv2018

Radiation reaction on a Brownian scalar electron in high-intensity fields

Radiation reaction against a relativistic electron is of critical importance since the experiment to check this "quantumness" becomes possible soon with an extremely high-intensity laser beam. However, there is a fundamental mathematical quest to apply any laser profiles to laser focusing and superposition beyond the Furry picture of its usual method by a plane wave. To give the apparent meaning of $q(χ)$ the quantumness factor with respect to a radiation process is absent. Thus for resolving the above questions, we propose stochastic quantization of the classical radiation reaction model for any laser field profiles, via the construction of the relativistic Brownian kinematics with the dynamics of a scalar electron and the Maxwell equation with a current by a Brownian quanta. This is the first proposal of the coupling system between a relativistic Brownian quanta and fields in Nelson's stochastic quantization. Therefore, we can derive the radiation field by its Maxwell equation, too. This provides us the fact that $q(χ)$ produced by QED is regarded as $\mathscr{P}(\varOmega_τ^{\mathrm{ave}})$ of an existence probability such that a scalar electron stay on its average trajectory.

math-ph↗

arXiv2017

A Brownian Particle and Fields II: Radiation Reaction as an Application

Radiation reaction has been investigated traditionally in classical dynamics and recently in non-linear QED for high-intensity field physics by high-intensity lasers. The non-linearity of QED is predicted as the coupling between a highly energetic electron and its radiation. However, the applicable range of external fields in the previous method of the Furry picture is just the case of a plane wave. In this Volume II, we aim the generalization of this applicable range by using the stochastic scalar electron model introduced in Volume I. We discuss the formulation of radiation reaction acting on a stochastic scalar electron and show the origin of this non-linearity correction in general conditions.

math-ph↗

arXiv2017

A Brownian Particle and Fields I: Construction of Kinematics and Dynamics

Tracking a real trajectory of a quantum particle still has been treated as the interpretation problem. It shall be expressed by a Brownian (stochastic) motion suggested by E. Nelson, however, the well-defined mechanism of field generation from a stochastic particle hasn't been proposed yet. For the improvement of this, I propose the extension of Nelson's quantum dynamics, for describing a relativistic scalar electron with its radiation equivalent to the Klein-Gordon particle and field system.

math-ph↗

arXiv2015

Radiation Reaction in High-Intensity Fields

After the development of a radiating electron model by P. A. M. Dirac in 1938, many authors have tried to reformulate this model so-called radiation reaction. Recently, this effect has become important in ultra-intense laser-electron (plasma) interactions. In our recent research, we found the stabilization method of radiation reaction by the QED vacuum fluctuation [PTEP 2014, 043A01 (2014), PTEP 2015, 023A01 (2015)]. On the other hand, the modification of the radiated field by highly intense incoming laser fields should be taken into account when the laser intensity is higher than 1022W/cm2, which could be achieved by the next generation ultra-short pulse 10PW lasers, like the ones under construction for the ELI-NP facility. In this paper, I propose the running charge-mass method for the description of the QED-based synchrotron radiation by high-intensity external fields with the stabilization by the QED vacuum fluctuation as an extension to the model by Dirac.

physics.plasm-ph↗

arXiv2014

Radiation Reaction in Quantum Vacuum

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model named "radiation reaction". P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the run-away solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. Therefore, it is desirable to stabilize this model of the radiation reaction for estimations. Via my recent research, I found a stabilized model of radiation reaction in quantum vacuum. This leads us to an updated Fletcher-Millikan's charge to mass ratio including radiation, de/dm, derived as the 4th order tensor measure. In this paper, I will discuss the latest update of the model and the ability of the equation of motion with radiation reaction in quantum vacuum via photon-photon scatterings.

physics.plasm-ph↗

arXiv2014

Stabilization of Radiation Reaction with Vacuum Polarization

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model. P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the run-away solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. For simulations in this research field, it is desirable to stabilize this model of the radiation reaction. In this paper, we will discuss this ability for radiation reaction with the inclusion of vacuum polarization. [Submitted to Progress of Theoretical and Experimental Physics (PTEP)]

physics.plasm-ph↗