Scalar radiation from a radially infalling source into a Schwarzschild black hole in the framework of quantum field theoryLeandro A. Oliveira, Luís C. B. Crispino and Atsushi HiguchiEur. Phys. J. C, 78 2 (2018) 133DOI: https://doi.org/10.1140/epjc/s10052-018-5604-8