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Item Rotating black hole with an anisotropic matter field as a particle accelerator(IOP Publishing Ltd, 2021) Ahmed Rizwan, C.L.; Naveena Kumara, A.; Hegde, K.; Ali, M.S.; Ajith, K.M.Recently, a generalised solution for Einstein equations for a rotating black hole, surrounded by matter field was proposed, which is the Kerr-Newman spacetime with an anisotropic matter [Phys. Rev. D. 101 064067]. Due to the negative radial pressure of the anisotropic matter, the solution possesses an additional hair along with the conventional mass, charge and spin. In this article we show that, this new class of black holes can act as a cosmic particle accelerator during the collision of two generic particles in its gravitational field in the ergo-region. The centre of mass energy of the particles shoots to an arbitrary high value in the vicinity of the event horizon for the extremal black hole. The physical conditions for the collision to take place are obtained by studying the horizon structure and circular particle motion. The results obtained are interesting from an astrophysical perspective. © 2021 IOP Publishing Ltd.Item Rotating 4D Gauss–Bonnet black hole as a particle accelerator(Academic Press Inc., 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.A.; Hegde, K.; Ali, M.S.; Ajith, K.M.We demonstrate that the rotating four-dimensional Gauss– Bonnet black hole can act as a particle accelerator with arbitrarily high centre-of-mass (CM) energy, when collision of two general particles takes place near the event horizon. The particles are at rest initially at infinity, and by fine tuning their angular momenta within a finite range, they are released so that they follow the time-like geodesics in the black hole spacetime, and the collision taking place on the equatorial plane is observed. The Gauss–Bonnet coupling constant ?, provides a deviation in the results, from that observed in the Kerr black hole. The horizon structure, the range of allowed angular momentum and the critical angular momentum depend on the value of ?. Our results show that the CM energy depends on the coupling parameter ? in addition to the black hole spin a. For extremal cases, the CM energy diverges at the horizon, suggesting that Gauss–Bonnet black hole can also act as a particle accelerator similar to a Kerr black hole. For the non-extremal case, there exists a finite upper bound on the CM energy, the maximal value of which depends on the parameter ?. © 2021 Elsevier Inc.