Abstract
We study polar quasinormal modes of relativistic stars in scalar-tensor theories, where we include a massive gravitational scalar field and employ the standard Brans-Dicke coupling function. For the potential of the scalar field we consider a simple mass term as well as a potential associated withR2gravity. The presence of the scalar field makes the spectrum of quasinormal modes much richer than the spectrum in General Relativity. We here investigate radial modes (l= 0) and quadrupole modes (l= 2). The general relativisticl= 0 normal modes turn into quasinormal modes in scalar-tensor theories, that are able to propagate outside of the stars. In addition to the pressure-led modes new scalar-ledϕ-modes arise. We analyze the dependence of the quasinormal mode frequencies and decay times on the scalar field mass.
Highlights
Following the first direct detections of gravitational waves, mostly emitted from merging black holes [1,2,3,4,5], there have been numerous further detections
We focus on quasinormal modes (QNMs) in alternative theories of gravity with an additional scalar degree of freedom
When considering radial perturbations in General Relativity, stars are seen to possess a family of normal modes with ω2 ∈ R, that become unstable beyond the maximum mass of the equation of state
Summary
Following the first direct detections of gravitational waves, mostly emitted from merging black holes [1,2,3,4,5], there have been numerous further detections. In General Relativity these modes are irrelevant for the ringdown, though, since radial perturbations cannot propagate outside the neutron stars. Because of their extreme compactness neutron stars represent excellent laboratories to test General Relativity and alternative theories of gravity (see e.g., [28,48,49,50]). The full polar QNMs have been addressed without making use of the Cowling approximation, where, in particular, ultra long lived modes were shown to exist in the radial sector [57]. The present paper is devoted to a more detailed study of the QNMs of the full polar perturbations of realistic neutron stars in massive STTs, extending the previous analyses [57,68,69]. We end the paper with our conclusions and an outlook
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