Quantum radiation from round-trip flying mirrors

Erasing a black hole leaves spacetime flat, so light passing through the region before any star forms and after the black hole's evaporation shows no time delay, just like a flying mirror that returns to its initial starting point. Quantum radiation from a round-trip flying mirror has not been solved despite the model's mathematical simplicity and physical clarity. Here, we solve the particle creation from worldlines that asymptotically start and stop at the same spot, resulting in interesting spectra and symmetries, including the time dependence of thermal radiance associated with Bose-Einstein and Fermi-Dirac Bogoliubov coefficients. Fourier analysis, intrinsically linked to the Bogoliubov mechanism, shows that a thermal Bogoliubov distribution does not describe the spin-statistics of the quantum field.