2017/04/19 by Shahar Hod · 1 citation
Physics and Astronomy · #astro-ph.HE #gr-qc #hep-th
paper · pdf · doi:10.1007/jhep06(2017)132
published as Journal of High Energy Physics 06, 132 (2017) · 9 pages
arxiv created 2017/04/19 · arxiv updated 2017/08/02
Exotic compact objects, horizonless spacetimes with reflective properties, have intriguingly been suggested by some quantum-gravity models as alternatives to classical black-hole spacetimes. A remarkable feature of spinning horizonless compact objects with reflective boundary conditions is the existence of a \it discrete set of critical surface radii, \rc( a;n)\n=∞n=1, which can support spatially regular static (\it marginally-stable) scalar field configurations (here a≡ J/M2 is the dimensionless angular momentum of the exotic compact object). Interestingly, the outermost critical radius rmaxc≡ maxn\rc( a;n)\ marks the boundary between stable and unstable exotic compact objects: spinning objects whose reflecting surfaces are situated in the region rc>rmaxc( a) are stable, whereas spinning objects whose reflecting surfaces are situated in the region rc<rmaxc( a) are superradiantly unstable to scalar perturbation modes. In the present paper we use analytical techniques in order to explore the physical properties of the critical (marginally-stable) spinning exotic compact objects. In particular, we derive a remarkably compact \it analytical formula for the discrete spectrum \rmaxc( a)\ of critical radii which characterize the marginally-stable exotic compact objects. We explicitly demonstrate that the analytically derived resonance spectrum agrees remarkably well with numerical results that recently appeared in the physics literature.