# Black hole merger estimates in Einstein-Maxwell and Einstein-Maxwell-dilaton gravity

## TL;DR

This paper estimates black hole merger parameters within Einstein-Maxwell-dilaton gravity, comparing results to Kerr-Newman black holes, to aid in testing gravity theories with gravitational wave data.

## Contribution

It provides the first conservative estimates of merger parameters in Einstein-Maxwell-dilaton gravity using test particle motion techniques.

## Key findings

- Final spins can be consistent with current observations.
- Merger signatures differ from those in general relativity.
- Analytic solutions are used for specific dilaton couplings.

## Abstract

The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here, we turn to one such theory in which the initial value problem for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present conservative estimates for the merger parameters (final spins, quasinormal modes) based on techniques that have worked well for ordinary gravity mergers and utilize information extracted from test particle motion in the final BH metric. The computation is developed in parallel for the modified gravity BHs (we specifically focus on the Kaluza-Klein value of the dilaton coupling, for which analytic BH solutions are known) and ordinary Kerr-Newman BHs. We comment on the possibility of obtaining final BHs with spins consistent with current observations.