English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

In this chapter, we review the eikonal technique to analytically deriveapproximate quasi-normal mode frequencies of black holes. We first review theprocedure in General Relativity and extend it to theories beyond GeneralRelativity. As an example of the latter, we focus on scalar Gauss-Bonnetgravity in which a scalar field can couple to the Gauss-Bonnet invariant in anarbitrary way in the action. In this theory, metric and scalar perturbationsare coupled in the polar sector, forcing the isospectrality to break and makingthe eikonal calculation more complex. We show that the analytic estimates canaccurately capture the numerical behavior of the quasi-normal mode frequencies,especially when the coupling constant of the theory is small.

Analytic estimates of quasi-normal mode frequencies for black holes in General Relativity and beyond