When two particles collide at the horizon of a black hole and one of them satisfies some critical conditions, the relative velocity between them can be arbitrarily large, thus the energy of the center-of-mass will reach infinity. Such a process is called BSW mechanism which can accelerate a particle to arbitrarily high energy. There are also some studies showing that a Kerr naked singularity can be more qualified as a particle accelerator for arbitrarily high energy. Previous researchers mainly concentrate on geodesic motion of particles. In this paper, we will take spinning particles which won't move along a timelike geodesic and carry more parameters into our consideration. By employing the Mathisson-Papapetrou-Dixon equation, we will prove that for a spinning particle in hyper-extremal Reissner-Nordstrom or Kerr spacetime where exists a naked singularity at $r=0$, its Effective Potential $V_{eff}=-\dot{r}^2$ must be able to reach zero within the interval $0 < r < M$, thus an ingoing particle will be able to turn back and then collide with another ingoing particle at $r=M$. If the spacetime is ${\bf slightly}$ hyper-extremal, the energy of center of mass $E_{cm}$ will be arbitrarily high.
It has been proved that arbitrarily high-energy collision between two particles can occur near the horizon of an extremal Kerr black hole as long as the energy $E$ and angular momentum $L$ of one particle satisfies a critical relation, which is called the BSW mechanism. Previous researchers mainly concentrate on geodesic motion of particles. In this paper, we will take spinning particle which won't move along a timelike geodesic into our consideration, hence, another parameter $s$ describing the particle's spin angular momentum was introduced. By employing the Mathisson-Papapetrou-Dixon equation describing the movement of spinning particle, we will explore whether a Kerr-Sen black hole which is slightly different from Kerr black hole can be used to accelerate a spinning particle to arbitrarily high energy. We found that when one of the two colliding particles satisfies a critical relation between the energy $E$ and the total angular momentum $J$, or has a critical spinning angular momentum $s_c$, a divergence of the center-of-mass energy $E_{cm}$ will be obtained.
It has been shown that black holes could be used as particle accelerators to create arbitrarily high center-of-mass (CM) energy if certain critical conditions are satisfied. Most studies so far are confined in four-dimensional spacetimes. In this paper, we present a systematic analysis on five-dimensional Myers-Perry black holes and find some novel properties compared to four-dimensional Kerr black holes. Firstly, we give a rigorous proof that untrhigh energy collisions cannot occur near a five-dimensional nonextremal black hole. Secondly, For extremal black holes, we find a critical condition on the particles' parameters causing ultraenergetic collisions. Thirdly, when the spacetime contains a naked singularity, we show that the CM energy could diverge at the singularity if one of the particle just bounces back at the singularity. Finally, we explore a special and important case where the naked singularity just begins to form. Surprisingly, the ultraenergetic collisions do not need any fine-turning in that case. However, we find that one of the conserved angular momentums must be nonzero.
We apply the new version of gedanken experiment designed recently by Sorce and Wald, to over-spin the 5-dimensional Myers-Perry black holes. As a result, the extremal black holes cannot be over-spun at the linear order. On the other hand, although the nearly extremal black holes could be over-spun at the linear order, this process is shown to be prohibited by the quadratic order correction. Thus no violation of the weak cosmic censorship conjecture occurs around the 5-dimensional Myers-Perry black holes.
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