We consider the emission of a photon by a scalar charged particle in a constant and uniform magnetic field. In contrast to the conventional approach with both photon and outgoing charge being assumed to be detected, we study the case where only the charge is detected and investigate the properties of the emitted photon. The background magnetic field is taken into account exactly in the calculations and the charge is described by relativistic Landau states. It is shown that the emitted photon state represents a twisted Bessel beam with a total angular momentum given by $\ell -{\ell }^{\prime }$, where $\ell$ and ${\ell }^{\prime }$ are angular momentum quantum numbers of the initial and final charged particle, respectively. The majority of photons emitted by unpolarized charges, especially in the hard x-ray and $\gamma$-ray range and in critical and subcritical magnetic fields, as compared to the Schwinger value of $H_c=4.4\times {10}^9\mathrm{T}$, turn out to be twisted with $\ell -{\ell }^{\prime }\gtrsim 1$.

• Received 3 March 2023
• Accepted 18 August 2023

DOI:https://doi.org/10.1103/PhysRevD.108.063007

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Published by the American Physical Society