Speaker
Description
In recent years, the gravitational self-force (GSF) has been successfully studied in Schwarzschild and Kerr black hole (BH) spacetimes. A test particle perturbing these spacetimes models a gravitational two-body system. After decoupling the radial and angular equations and performing a Fourier transform in the time variable, one is ultimately left with a main radial equation. This equation can be solved perturbatively using various approximation schemes: the Post-Newtonian (PN) expansion, which assumes slow motion; the Post-Minkowskian (PM) expansion, which assumes a weak field; and the Mano-Suzuki-Takasugi (MST) expansion, which uses hypergeometric functions that satisfy the correct boundary conditions—purely ingoing waves at the horizon and outgoing waves at infinity.
These same techniques are now being applied to recently discovered solutions of the Einstein-Maxwell equations in five dimensions, which include both electric and magnetic fluxes and are known as Topological Stars (TS). In a certain parameter regime, this solution describes a smooth, horizonless geometry; in the complementary regime, it reduces to a Schwarzschild solution with an extra compactified dimension.
The emission of scalar waves due to the presence of a small massive particle moving along circular and hyperbolic-like geodesics in the TS geometry is investigated. Furthermore, fundamental observables such as energy and angular momentum losses are computed, along with the deflection angle in geodesic scattering.
