# Dilatonic Imprints on Exact Gravitational Wave Signatures

## TL;DR

This paper analytically investigates how dilatonic couplings affect gravitational wave signatures from black hole mergers, revealing distinctive imprints that could indicate the presence of scalar fields like those in string theory.

## Contribution

It provides the first analytical calculation of gravitational wave signatures for dilatonic black hole mergers across different coupling constants, highlighting observable imprints of scalar fields.

## Key findings

- No coalescence orbits for string theory black holes (a=1).
- Memory effect observed in all cases.
- Exponential suppression of late-time merger signatures at a=1/√3.

## Abstract

By employing the moduli space approximation, we analytically calculate the gravitational wave signatures emitted upon the merger of two extremally charged dilatonic black holes. We probe several values of the dilatonic coupling constant $a$, and find significant departures from the Einstein--Maxwell ($a=0$) counterpart studied in arXiv:1704.08520. For (low energy) string theory black holes $(a=1)$ there are no coalescence orbits and only a memory effect is observed, whereas for an intermediate value of the coupling $(a=1/\sqrt{3})$ the late-time merger signature becomes exponentially suppressed, compared to the polynomial decay in the $a=0$ case without a dilaton. Such an imprint is in principle observable and could reveal the presence of a scalar field (as for example predicted by string theory) in black hole mergers.