Orateur
Dr
Christiana Pantelidou
(University College Dublin)
Description
Black hole quasinormal modes (QNMs) are associated with a non-normal evolution problem and therefore do not form an orthogonal basis under natural choices of inner product. However, special bilinear products can be introduced that establish orthogonality relations and allow the definition of QNM excitation coefficients. In this talk, we study these constructions in the hyperboloidal framework, where QNM solutions are smooth and the description of non-modal physics becomes more natural. We discuss why the associated bilinear products nevertheless remain divergent, review regularisation procedures that produce finite and well-defined expressions, and examine alternative formulations involving flux terms.