Super-Penrose process for extremal rotating neutral white holes (Q828778)

The topic of this article refers to a very well known effect from the physics of black holes and white holes: Penrose and super-Penrose processes extraction of energy from black holes. It was suggested initially by \textit{R. Penrose} in [``Gravitational collapse: the role of general relativity'', Riv. Nuovo Cim. 1, 252--276 (1969; \url{doi:10.1023/A:1016578408204})] as a result of analysis of geodesics around a rotating (Kerr) black hole in the ergosphere of a black hole. Namely, in the ergosphere of a rotating black hole some orbits could have negative total energy from the viewpoint of a distant observer, so that for particles falling from the infinity and decaying inside the ergosphere some decay products could be captured on such negative energy orbits. Then other decay particles could gain energy and escape from the black hole increasing their own energy. This effect makes energy extraction possible from a rotating (Kerr) black hole. Subsequently the developments followed on two various ways: most of physicists drew attention on the wave analogue of this energy extraction process: the so called superradiation, suggested by \textit{Ya. B. Zeldovich} [Zh. Eksp. Teoret Fiz. 14, 270 (1971)] and \textit{Ch. W. Misner} [``Stability of Kerr black holes against scalar perturbation'', Bull. Am. Phys. Soc. 17, 472 (1972)], while other with some delay concentrated themselves on the implications of the new feature on astrophysical consequences. Actually the second part of research, implying classical particles, includes research of various black holes and white holes types, naked singularities, Kerr, Reissner-Nordstrom, or Kerr-Newman black holes in order to find the most effective one from the viewpoint of energy extraction scenario. It was realised, that if the case of decaying single particle is not efficient from the viewpoint of energy extraction, the case when capture on negative energy orbit occurs as a result of a collision of many particles. In some cases the effectiveness could reach 1391\% [\textit{J. D. Schnittman}, Gen. Relativ. Gravitation 50, No. 6, Paper No. 77, 27 p. (2018; Zbl 1392.83062)]. The resulting particles can escape with high energies from the ergosphere serving a probe of high-energy physics and general relativity. Another important feature of the collisional super-Penrose process consists in its potential to enhance annihilation of dark matter particles in the vicinity of a supermassive black hole. In this article the author considers collisions of 2 particles: 1 and 2 near the horizon of an extremal Reissner-Nordstrom black hole that produces 2 other particles 3 and 4. There exists such a scenario that both new particles fall into a black hole. One of them emerges from the white hole horizon in the asymptotically flat region, and the other oscillates between turning points. However, the unbounded energies \(E\) at infinity turn out to be impossible for any finite angular momenta \(L_{3,4}\). Then, in this case the situation for such a white hole scenario seems to be opposite to the situation with a black hole, when the super-Penrose process is found to be possible for the Reissner-Nordstrom metric even for \(L_i= 0\). However, if \(L_{3,4}\) themselves are unbounded, the super Penrose process does exist for white holes.