**Publication date:** Nov 2017

**Abstract:**

We study ultrahigh-energy particle collisions and optical effects in the

extraordinary class of mining braneworld Kerr-Newman (KN) naked

singularity spacetimes, predicting extremely high efficiency of

Keplerian accretion, and compare the results to those related to the

other classes of the KN naked singularity and black hole spacetimes. We

demonstrate that in the mining KN spacetimes the ultrahigh center-of-

mass energy occurs for collisions of particles following the extremely-

low-energy stable circular geodesics of the „mining regime,“ colliding

with large family of incoming particles, e.g., those infalling from the

marginally stable counter-rotating circular geodesics. This is

qualitatively different situation in comparison to the standard KN naked

singularity or black hole spacetimes where the collisional ultrahigh

center-of-mass energy can be obtained only in the near-extreme

spacetimes. We also show that observers following the stable circular

geodesics of the mining regime can register extremely blue-shifted

radiation incoming from the Universe, and see strongly deformed sky due

to highly relativistic motion along such stable orbits. The strongly

blue-shifted radiation could be thus a significant source of energy for

such orbiting observers.

**Authors:**

Stuchlík, Zdeněk; Blaschke, Martin; Schee, Jan;