arXiv subjects

Mandar Patil

Publications and source records attributed to Mandar Patil.

23 records · Page 2Linked to original sources

arXiv2012

Acceleration of particles by Janis-Newman-Winicour singularities

We examine here the acceleration of particles and high energy collisions in the the Janis-Newman- Winicour (JNW) spacetime, which is an extension of the Schwarzschild geometry when a massless scalar field is included. We show that while the center of mass energy of collisions of particles near the event horizon of a blackhole is not significantly larger than the rest mass of the interacting particles, in an analogous situation, it could be arbitrarily large in the JNWspacetime near the naked singularity. The high energy collisions are seen to be generic in the presence of a photon sphere in the JNW spacetime, whereas an extreme fine-tuning of the angular momentum of the colliding particles is required when the photon sphere is absent. The center of mass energy of collision near the singularity grows slowly for small and extremely large deviations from the Schwarzschild blackhole, but for intermediate strengths of the scalar field it rises moderately fast. As a possible and potentially interesting application, we point out that the presence of such high energy collissions may help the blackhole configurations to be distinguished from a naked singularity.

gr-qc↗

arXiv2011

Kerr Naked Singularities as Particle Accelerators

We investigate here the particle acceleration by Kerr naked singularities. We consider a collision between particles dropped in from infinity at rest, which follow geodesic motion in the equatorial plane, with their angular momenta in an appropriate finite range of values. When an event horizon is absent, an initially infalling particle turns back as an outgoing particle, when it has the angular momentum in an appropriate range of values, which then collides with infalling particles. When the collision takes place close to what would have been the event horizon in the extremal case, the center of mass energy of collision is arbitrarily large, depending on how close is the overspinning Kerr geometry to the extremal case. Thus the fast rotating Kerr configurations if they exist in nature could provide an excellent cosmic laboratory to probe ultra-high-energy physics.

gr-qc↗

arXiv2011

High Energy Particle Collisions in Superspinning Kerr Geometry

We investigate here the particle acceleration and high energy collision in the Kerr geometry containing a naked singularity. We show that the center of mass energy of collision between two particles, dropped in from a finite but arbitrarily large distance along the axis of symmetry is arbitrarily large, provided the deviation of the angular momentum parameter from the mass is very small for the Kerr naked singularity. The collisions considered here are between particles, one of them ingoing and the other one being initially ingoing but which later emerges as an outgoing particle, after it suffers a reflection from a spatial region which has a repulsive gravity in the vicinity of the naked singularity. High energy collisions take place around a region which marks a transition between the attractive and repulsive regimes of gravity. We make a critical comparison between our results and the BSW acceleration mechanism [M. Banados, J. Silk, and S. M. West, Phys. Rev. Lett. 103, 111102 (2009).] for extremal Kerr blackholes, and argue that the scenario we give here has certain distinct advantages. If compact objects exist in nature with exterior Kerr superspinning geometry then such high energy collisions would have a significant impact on the physical processes occurring in its surrounding and could possibly lead to their own observational signatures. As an aside we also suggest a curious Gedanken collider physics experiment which could in principle be constructed in this geometry.

gr-qc↗

arXiv2011

Naked Singularities as Particle Accelerators II

We generalize here our earlier results on particle acceleration by naked singularities. We showed recently[1] that the naked singularities that form due to gravitational collapse of massive stars provide a suitable environment where particles could get accelerated and collide at arbitrarily high center of mass energies. However, we focussed there only on the spherically symmetric gravitational collapse models, which were also assumed to be self-similar. In this paper, we broaden and generalize the result to all gravitational collapse models leading to the formation of a naked singularity as final state of collapse, evolving from a regular initial data, without making any prior restrictive assumptions about the spacetime symmetries such as above. We show that when the particles interact and collide near the Cauchy horizon, the energy of collision in the center of mass frame will be arbitrarily high, thus offering a window to the Planck scale physics. We also consider the issue of various possible physical mechanisms of generation of such very high energy particles from the vicinity of naked singularity. We then construct a model of gravitational collapse to a timelike naked singularity to demonstrate the working of these ideas, where the pressure is allowed to be negative but the energy conditions are respected. We show that a finite amount of mass-energy density has to be necessarily radiated away from the vicinity of the naked singularity as the collapse evolves. Therefore the nature of naked singularities, both at classical and quantum level could play an important role in the process of particle acceleration, explaining the occurrence of highly energetic outgoing particles in the vicinity of Cauchy horizon that participate in extreme high energy collisions.

gr-qc↗

arXiv2010

Naked singularities as particle accelerators

We investigate here the particle acceleration by naked singularities to arbitrarily high center of mass energies. Recently it has been suggested that black holes could be used as particle accelerators to probe the Planck scale physics. We show that the naked singularities serve the same purpose and probably would do better than their black hole counterparts. We focus on the scenario of a self-similar gravitational collapse starting from a regular initial data, leading to the formation of a globally naked singularity. It is seen that when particles moving along timelike geodesics interact and collide near the Cauchy horizon, the energy of collision in the center of mass frame will be arbitrarily high, thus offering a window to Planck scale physics.

gr-qc↗