Talk detail

Participant	Sampaio, Marco
Institution	Universidade de Aveiro and CIDMA - Campus de Santiago - Aveiro - Aveiro - Portugal

Session	ES2	Accepted		Order	Time
Talk	Oral abstract	Title	Exact results in gravitational shock wave collisions in D-dimensions
Coauthors
Abstract	I discuss the construction of the metric describing a (head on) collision of two gravitational shock waves in D-dimensions, which yields the production of a black hole. Despite using a perturbative technique, first proposed and studied by D'Eath and Payne in four dimensions, we unveil exact results for all D -- JHEP 1412 (2014) 119 -- some of which are valid to all orders in perturbation theory. We show that the angular dependence of the radiated power is fully determined (and factorizes) to all orders in perturbation theory, a result which was suggested by low order studies in 4D in the 90s, but which had not been proved. This also establishes an exact correspondence between the order of the perturbative expansion and of the angular expansion around the axis of symmetry. We show that such results are a consequence of a conformal symmetry combined with the flat space asymptotics at null infinity. Finally we construct a Penrose-Carter diagram for this setup (which sets the stage for the evaluation of the solution at higher orders), and comment on analytic results which suggest the possibility of a general structure beyond the leading order.
Pdf file

Session	BH4	Accepted		Order	Time
Talk	Oral abstract	Title	Marginal Proca and Scalar clouds in Reissner-Nordström
Coauthors
Abstract	Quasibound states with complex frequencies are known to exist around Kerr black holes, which can either grow in time (if in the superradiant regime) or decay. At the threshold between superradiant and non-superradiant modes, true bound states (or clouds) are allowed with a purely real frequency, which often have non-linear counterparts, e.g. Kerr black holes with scalar hair. We study massive spin 0 (scalar) and 1 (Proca) fields around Reissner-Nordström black holes (Phys. Rev. D 90, 064004) which also allow for superradiance. We compute the quasi-bound state frequencies and establish that no bound states exist. Nevertheless, we find non-trivial configurations with an arbitrarily small imaginary part of the frequency (outside the superradiant regime), which can be arbitrarily long lived, thus marginally bound. We finish with comments on the possibility of finding non-linear counterparts to such linear configurations.
Pdf file