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Exploring tidal effects of coalescing binary neutron stars in numerical relativity

We study gravitational waves emitted in the late inspiral stage of binary neutron stars by analyzing the waveform obtained in numerical-relativity simulations. For deriving the physical gravitational waveforms from the numerical results, the resolution extrapolation plays an essential role for our simulations. The extrapolated gravitational-wave phases are compared with those calculated in the post-Newtonian (PN) and effective-one-body (EOB) formalisms including corrections of tidal effects. We show that the extrapolated gravitational-wave phases in numerical relativity agree well with those by the PN and EOB calculations for most of the inspiral stage except for a tidally-dominated, final inspiral stage, in which the PN and EOB results underestimate the tidal effects. Nevertheless, the accumulated phase difference between our extrapolated results and the results by the PN/EOB calculations is at most 1--3 radian in the last 15 cycles.