Relic Gravitational Wave Conversion into Photons in the Cosmological Magnetic Field

The article evaluates the amplitude suppression for the relict gravitational waves with a frequency of \({{10}^{{ - 16}}}- {{10}^{{ - 18}}}\) Hz due to their conversion into electromagnetic waves under the influence of a cosmological magnetic field during the era of radiation dominance (RD). At first, a system of equations was obtained for the joint propagation of gravitational and electromagnetic waves in an external magnetic field in the Friedmann–Lemaitre–Robertson–Walker metric and the interaction of electromagnetic waves with the primary plasma was taken into account. Then the resulting system is solved numerically in the approximation of a uniform cosmological magnetic field with a strength corresponding to the modern value of 1 nG (for the RD epoch the magnetic field strength increases as the inverse scale factor squared). Finally a conclusion was made about the insignificant influence of the considered conversion effect on the amplitude of long-wave relic gravitational waves.