# Scalar clouds around Kerr-Sen black holes

## TL;DR

This study explores the existence and properties of scalar clouds around Kerr-Sen black holes, revealing limits on their mass and charge, and contrasting these with Kerr-Newman and Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes.

## Contribution

It provides the first numerical analysis of scalar clouds around Kerr-Sen black holes, highlighting their parameter space limitations and differences from other black hole solutions.

## Key findings

- Scalar clouds exist within finite parameter regions.
- Maximum cloud mass and charge are independent of black hole angular velocity for extremal Kerr-Sen.
- Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes cannot support scalar clouds.

## Abstract

In this paper, the behaviour of a charged massive scalar test field in the background of a Kerr-Sen black hole is investigated. A kind of stationary solutions, dubbed scalar clouds, are obtained numerically and expressed by the existence lines in the parameter space. We show that for fixed background and a given set of harmonic indices, the mass and charge of the scalar clouds are limited in a finite region in the parameter space of the scalar field. Particularly, the maximum values of the mass and charge of the clouds around extremal Kerr-Sen black holes are independent of the angular velocity of the black hole, whereas those in the extremal Kerr-Newman background depend on the angular velocity. In addition, it is demonstrated that, as the static limit of Kerr-Sen black hole, Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole can not support scalar cloud.