Polarisationseffekte in modifizierten Versionen des QED-Vakuums
Zusammenfassung der Projektergebnisse
In this theoretical project, various strong-field polarization effects occurring in different kinds of quantum vacua were studied. Differences and similarities among the considered phenomena were analyzed and possible experimental detection schemes proposed. (1) The spontaneous production of electron-positron pairs from the vacuum – in a field configuration composed of a high-frequency electric mode of weak intensity and a strong constant electric field – was investigated. Asymptotic expressions for the single-particle distribution function ruling this nonperturbative process were established by considering the low-density approximation in the Boltzmann-Vlasov equation. An analytical formula for the density rate of created particles was derived that interpolates between the tunneling and multiphoton regimes. It has been shown that – under appropriate circumstances – the created plasma of electrons and positrons might reach densities for which their recombinations into high-energy photons occur copiously. On the basis of this feature, an experimental setup for observing the dynamically assisted Schwinger effect was put forward. (2) In a vicinity of the Fermi surface, bandgapped graphene layers allow for closely simulating the vacuum of quantum electrodynamics and, thus, its yet unverified strong-field phenomenology with accessible field strengths. This striking feature has been exploited to investigate a plausible materialization of both the dynamically assisted pair production and the Breit-Wheeler effect through analogous generation processes of light but massive pairs of Dirac quasiparticles in graphene. To simulate the former process, a field configuration similar to the one used in QED was considered. It was shown that the presence of a weak but fast-oscillating electric mode can strongly increase the interband transitions of massive Dirac pairs as compared with a setup driven by the strong field only. The efficiency of the process was contrasted, moreover, with the case of gapless graphene to highlight the role played by the quasiparticle mass. In contrast, the analog of the Breit-Wheeler pair production was investigated by considering graphene exposed to monochromatic plane laser waves. This scenario revealed that the two-dimensionality of graphene induces peculiar differences in the production rates with respect to the QED counterpart if the creation of an electron-hole pair occurs by an odd number of photons. (3) The vacuum polarization tensor resulting from axion electrodynamics was obtained and the corresponding modification to the Coulomb potential derived. In connection, the plausible distortion of the Lamb-shift in hydrogen-like atoms was established and the scopes for searching axion-like particles in high-precision atomic spectroscopy and in experiments of Cavendish-type were elucidated. It was shown that these hypothetical degrees of freedom are ruled out as plausible candidates for explaining the proton radius anomaly in muonic hydrogen. Furthermore, it has been argued that, in the presence of a curved magnetic field background, the vacuum polarization tensor linked to axionelectrodynamics might induce a canalization of photons along the magnetic field lines at the surface of a neutron star. However, this sort of capture of gamma photons prior to the production of a pair would prevent the existence of an electron-positron plasma, which is essential, though, for explaining the pulsar radiation mechanism. This incompatibility was used to limit the axion parameter space. The bounds resulting from this analysis improved existing outcomes in the mass region m ∼ 10^−10 − 10^−5 eV.
Projektbezogene Publikationen (Auswahl)
- Axion-modified photon propagator, Coulomb potential, and Lamb shift. Phys. Rev. D 98, 115008 (2018)
S. Villalba-Chávez, A. Golub and C. Müller
(Siehe online unter https://doi.org/10.1103/PhysRevD.98.115008) - Signatures of the Schwinger mechanism assisted by a fast-oscillating electric field. Phys. Rev. D 100, 116018 (2019)
S. Villalba-Chávez and C. Müller
(Siehe online unter https://doi.org/10.1103/PhysRevD.100.116018) - Simulating dynamically assisted production of Dirac pairs in gapped graphene monolayers. Phys. Rev. D 99, 016025 (2019)
I. Akal, R. Egger, C. Müller and S. Villalba-Chávez
(Siehe online unter https://doi.org/10.1103/PhysRevD.99.016025) - Dimensionality-driven photoproduction of massive Dirac pairs near threshold in gapped graphene monolayers. Phys. Rev. Lett. 124, 110403 (2020)
A. Golub, R. Egger, C. Müller and S. Villalba-Chávez
(Siehe online unter https://doi.org/10.1103/PhysRevLett.124.110403) - Magnetic dominance of axion electrodynamics: photon capture effect and anisotropy of Coulomb potential. Eur. Phys. J. C 81, 331 (2021)
S. Villalba-Chávez, A. E. Shabad and C. Müller
(Siehe online unter https://doi.org/10.1140/epjc/s10052-021-09046-3)
