Generation of an electromagnetic field nonminimally coupled to gravity during Higgs inflation

Oleksandr Sobol
2021
Article

In the framework of Higgs inflation, we consider the electromagnetic field nonminimally coupled to gravity via the parity-preserving proportional to RF2 and parity-violating proportional to RF (F) over tilde terms. Using the perturbation theory to the leading order in these couplings, we study the generation of the electromagnetic field during the inflation stage. We derive the effective kinetic and axial coupling functions arising in the Einstein frame in the usual metric as well as Palatini formulations of gravity. For both formulations, we determine the power spectrum, energy density, and helicality of the generated electromagnetic fields for different values of the nonminimal coupling constants. Finally, we estimate the maximal present-day magnitude of the magnetic field as 10(-14)-10(-15) G with the correlation length of order 10 pc.

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Oleksandr Sobol
2021
Article

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https://infoscience.epfl.ch/record/288108?ln=fr

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Backreaction of electromagnetic fields and the Schwinger effect in pseudoscalar inflation magnetogenesis

Oleksandr Sobol

We study magnetogenesis in axionlike inflation driven by a pseudoscalar field phi coupled axially to the electromagnetic (EM) field (beta/M-p)phi F-mu nu(F) over tilde mu nu with dimensionless coupling constant beta. A set of equations for the inflaton field, scale factor, and expectation values of quadratic functions of the EM field is derived. These equations take into account the Schwinger effect and the backreaction of generated EM fields on the Universe expansion. It is found that the backreaction becomes important when the EM energy density reaches the value rho(EM) similar to (root 2 epsilon/beta)rho(inf) (epsilon is the slow-roll parameter and rho(inf) is the energy density of the inflaton) slowing down the inflaton rolling and terminating magnetogenesis. The Schwinger effect becomes relevant when the electric energy density exceeds the value rho(E) similar to alpha(-3)(EM)(rho(2)(tot)/M-p(4)), where rho(tot) = 3H(2)M(p)(2) is the total energy density and alpha(EM) is the EM coupling constant. For large beta, produced charged particles could constitute a significant part of the Universe energy density even before the preheating stage. Numerically studying magnetogenesis in the alpha-attractor model of inflation, we find that it is possible to generate helical magnetic fields with the maximal strength 10(-15) G, however, only with the correlation length of order 1 pc at present.

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Vasily Zabelin

Two-dimensional (2D) photonic crystals (PhCs) operating in the near-infrared wavelengths are promising candidates for novel integrated optics applications. In this work the optical properties of the Bloch modes in 2D photonic crystals have been investigated theoretically using different numerical methods. The plane wave expansion (PWE) method have been formulated in a general form for arbitrary 2D photonic crystal and applied for detailed analysis of the properties of the Bloch modes. The k space based and the frequency based PWE methods have been derived and used, which allowed us to analyze both propagating and evanescent modes. The guided mode expansion method has been used to take into account three-dimensional distribution of the electromagnetic field in the planar photonic crystals and improve the accuracy of the analysis. A new method of calculation of the sensitivity of the photonic crystal optical properties to small variations of the photonic crystal parameters has been developed. This method is based on the perturbation theory and allows fast and accurate estimation of the optical properties corrections as a result of a change the parameters of the photonic crystal. The developed methods have been used for design and analysis of different photonic crystal based structures, such as cavities, waveguides, coupled-cavity waveguides and polarization beam splitter. The developed methods proved to be efficient and accurate tools for modelling two-dimensional photonic crystal properties and design of photonic crystal based devices.

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An Analytical Model to Evaluate the Radiated Power Spectrum of a Multipactor Discharge in a Parallel-Plate Region

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This paper is aimed at studying the electromagnetic radiation pattern of a multipactor discharge occurring in a parallel-plate waveguide. The proposed method is based on the Fourier expansion of the multipactor current in terms of time-harmonic currents radiating in the parallel-plate region. Classical radiation theory combined with the frequency domain Green's function of the problem allows the calculation of both the electric and the magnetic radiated fields. A novel analytical formula for the total radiated power of each multipactor harmonic has been derived. This formula is suitable for predicting multipactor with the third-harmonic technique. The proposed formulation has been successfully tested with a particle-in-cell code.

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