Eur. Phys. J. Plus (2019) 134: 46
https://doi.org/10.1140/epjp/i2019-12392-9

Regular Article

Quasinormal modes of compact objects in alternative theories of gravity

¹ Institut für Physik, Universität Oldenburg, Postfach 2503, D-26111, Oldenburg, Germany
² Theoretical Astrophysics, Eberhard Karls University of Tübingen, 72076, Tübingen, Germany
³ INRNE, Bulgarian Academy of Sciences, 1784, Sofia, Bulgaria
⁴ Division of Theoretical Physics, Rudjer Bošković Institute, Bijenička 54, 10000, Zagreb, Croatia
⁵ Escuela de Física, Universidad Industrial de Santander, 680002, Bucaramanga, Colombia
⁶ Department of Theoretical Physics, Faculty of Physics, Sofia University, 1164, Sofia, Bulgaria
⁷ Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Acad. G. Bonchev Street 8, 1113, Sofia, Bulgaria

^* e-mail: jose.blazquez.salcedo@uni-oldenburg.de

Received: 5 November 2018
Accepted: 12 November 2018
Published online: 31 January 2019

Abstract

We address quasinormal modes of compact objects in several alternative theories of gravity. In particular, we focus on black holes and neutron stars with scalar hair. We consider black holes in dilaton-Einstein-Gauß-Bonnet theory, and in a generalized scalar-Einstein-Gauß-Bonnet theory. In the latter case scalarized black holes arise, and we study the stability of the different branches of solutions. In particular, we discuss how the spectrum of quasinormal modes is changed by the presence of a non-trivial scalar field outside the black hole horizon. We discuss the existence of an (effective) minimum mass in these models, and how the spectrum of modes becomes richer as compared to general relativity, when a scalar field is present. Subsequently, we discuss the effect of scalar hair for realistic neutron star models. Here we consider R² gravity, scalar-tensor theory, a particular subsector of Horndeski theory with a non-minimal derivative coupling, and again dilatonic-Einstein-Gauß-Bonnet theory. Because of the current lack of knowledge on the internal composition of the neutron stars, we focus on universal relations for the quasinormal modes, that are largely independent of the equations of state and thus the matter content of the stars.