Fundamental physical features of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in strong laser fields

Theoretically predicted fundamental features in the process of resonant spontaneous bremsstrahlung radiation during the scattering of ultrarelativistic electrons with energies of the order ∼ 100 GeV by the nuclei in strong laser fields with intensities up to I ∼ 1024 W cm−2. Under resonant conditions, an intermediate electron in the wave field enters the mass shell. As a result, the initial second-order process by the fine structure constant is effectively reduced to two first-order processes: laser-stimulated Compton effect and laser-assisted Mott process. The resonant kinematics for two reaction channels (A and B) is studied in detail. An analytical resonant differential cross-section with simultaneous registration of the frequency and the outgoing angle of a spontaneous gamma-quantum for channels A and B is obtained. The resonant differential cross section takes the largest value with a small number of absorbed laser photons. In this case, the resonant cross-section is determined by one parameter, depending on the small transmitted momenta, as well as the resonance width. In strong fields, spontaneous gamma quanta of small energies are most likely to be emitted compared to the energy of the initial electrons. At the same time, the angular width of the radiation of such gamma quanta is the largest. With an increase in the number of absorbed laser photons, the resonant cross-section decreases quite quickly, and the resonant frequency of spontaneous gamma quanta increases. It is shown that the resonant differential cross-section has the largest value in the region of average laser fields (I ∼ 1018 W cm−2) and can be of the order of ∼ 1 0 19 in units Z 2 α r e 2 . With an increase in the intensity of the laser wave, the value of the resonant differential cross-section R r e s max decreases and for the intensity I ∼ 1024 W cm−2 is R r e s max ≲ 1 0 7 in units Z 2 α r e 2 . The obtained results reveal new features of spontaneous emission of ultrarelativistic electrons on nuclei in strong laser fields and can be tested at international laser installations.

Scattering of Fermions by a Magnetic Dipole Field

In this paper we study the problem of fermions scattering by the field of a magnetic dipole in Minkowski space-time. The amplitude and differential cross section for scattering of massive fermions are obtained using the exact solution of the Dirac equation written in the helicity basis. We found that the most probable transitions are those that scatter the fermions perpendicular to the direction of the magnetic field and we consider only the transverse momenta in our analysis. The differential cross section behavior in terms of scattering angle and energy is graphically analysed and we perform a comparative study with the Coulomb scattering.

Electrodisintegration of Deuteron into Dark Matter and Proton Close to Threshold

We discuss an investigation of the dark matter decay modes of the neutron, proposed by Fornal and Grinstein (2018–2020), Berezhiani (2017, 2018) and Ivanov et al. (2018) for solution of the neutron lifetime anomaly problem, through the analysis of the electrodisintegration of the deuteron d into dark matter fermions χ and protons p close to threshold. We calculate the triple-differential cross section for the reaction e−+d→χ+p+e− and propose to search for such a dark matter channel in coincidence experiments on the electrodisintegration of the deuteron e−+d→n+p+e− into neutrons n and protons close to threshold with outgoing electrons, protons, and neutrons in coincidence. An absence of neutron signals should testify to a detection of dark matter fermions.

The Effect of Unparticle in the Processes \(e^{+}e^{-}\rightarrow \gamma \gamma\) and \(\gamma e^{-}\rightarrow U^{\mu }e^{-}\) when the \(e^{+},e^{-}\) Beams Are Polarized in Unparticle Physics

We investigate the influence of unparticle physics on the positron-electron collider via the scalar unparticle and electron exchange. From computing the contribution of the unparticle exchange to the cross-section (CS) as well as evaluating the dependence of differential cross-section (DCS) on the scattering angle , we calculate the production of vector unparticle in the photon-electron collider in s- and t- channels such as missing energy distribution. Besides, we also found that the polarization of the beams also significantly contributes to the CS and DCS of the unparticle production.

Benchmark Angle-Differential Cross-Section Ratios for Excitation of the 4p5s Configuration in Krypton

Benchmark intensity ratio measurements of the energy loss lines of krypton for excitation of the 4p61S0→4p55s[3/2]2, 4p55s[3/2]1, 4p55s′[1/2]0, and 4p55s′[1/2]1 transitions are reported, these being the lowest electronic excitations for krypton. The importance of these ratios as stringent tests of theoretical electron scattering models for the noble gases is discussed, as well as the role of spin-exchange and direct processes regarding the angular dependence of these ratios. The experimental data are compared with predictions from fully-relativistic B-spline R-matrix (close-coupling) calculations.