Abstract

Binary systems with extreme-mass ratio are one of the most promising sources of Gravitational-Waves (GWs) for space-based detectors like LISA (the Laser Interferometer Space Antenna). These binaries provide long and complex GW waveforms, whose phase and timing are determined by the orbit of the SCO in the MBH background geometry. Their detection will offer the possibility of exploring the strong gravitational field in the vicinity of the MBH and simultaneously test the theory of gravity governing the system. In this regard, the development of a practical methodology for computing the generation and propagation of GWs in theories of gravity different from General Relativity (GR) has only recently begun. In this talk, we give a general overview about the main features of Extreme-Mass-Ratio Inspirals (EMRIs) and present a first parameter estimation analysis to determine to what extent a space-based GW observatory like LISA could distinguish between GR and other alternative theory of gravity. In particular, we focus on a modified theory of gravity parametrized by a four-dimensional Chern-Simons (CS) gravitational term. We model the motion of the SCO as evolving geodesics including Radiation-Reaction (RR) effects and the GWs are described with a multipolar formalism up to quadrupolar order. We use these model waveforms to study a five-dimensional space of capture-event parameters, including the CS parameter, finding that a GW detector like LISA could discriminate between GR and Dynamical Chern-Simons modified theory within a fractional error of ~10E-2, which is three orders of magnitude better than current Solar System bounds.