INTO THE LAIR: GRAVITATIONAL-WAVE SIGNATURES OF DARK MATTER

Abstract

The nature and properties of dark matter (DM) are both outstanding issues in\nphysics. Besides clustering in halos, the universal character of gravity\nimplies that self-gravitating compact DM configurations might be spread\nthroughout the universe. The astrophysical signature of these objects may be\nused to probe fundamental particle physics, or even to provide an alternative\ndescription of compact objects in active galactic nuclei. Here we discuss the\nmost promising dissection tool of these configurations: the inspiral of a\ncompact stellar-size object and consequent gravitational-wave emission. The\ninward motion of this "test probe" encodes unique information about the nature\nof the central, supermassive DM configuration. When the probe travels through\nsome compact DM profile we show that, within a Newtonian approximation, the\nquasi-adiabatic evolution of the inspiral is mainly driven by DM accretion into\nthe small compact object and by dynamical friction, rather than by\ngravitational-wave radiation-reaction. These effects circularize the orbits and\nleave a peculiar imprint on the gravitational waves emitted at late time. When\naccretion dominates, the frequency and the amplitude of the gravitational-wave\nsignal produced during the latest stages of the inspiral are nearly constant.\nIn the exterior region we study a relativistic model in which the inspiral is\ndriven by the emission of gravitational and scalar waves. Resonances in the\nenergy flux appear whenever the orbital frequency matches the mass of the DM\nparticle and they correspond to the excitation of the central object's\nquasinormal frequencies. Unexpectedly, these resonances can lead to large\ndephasing with respect to standard inspiral templates, to such an extent as to\nprevent detection with matched filtering techniques. We discuss some\nobservational consequences of these effects for gravitational-wave detection.\n