Gravitational-wave imprints of nonconvex dynamics in binary neutron star mergers
Giuseppe Rivieccio, D. Guerra, Milton Ruiz, José A. Font
Abstract
Explaining gravitational-wave (GW) observations of binary neutron star (BNS) mergers requires an understanding of matter beyond nuclear saturation density. Our current knowledge of the properties of high-density matter relies on electromagnetic and GW observations, nuclear physics experiments, and general relativistic numerical simulations. In this paper we perform numerical-relativity simulations of BNS mergers subject to nonconvex dynamics, allowing for the appearance of expansive shock waves and compressive rarefactions. Using a phenomenological nonconvex equation of state we identify observable imprints on the GW spectra of the remnant. In particular, we find that nonconvexity induces a significant shift in the quasiuniversal relation between the peak frequency of the dominant mode and the tidal deformability (of order $\mathrm{\ensuremath{\Delta}}{f}_{\mathrm{peak}}\ensuremath{\gtrsim}380\text{ }\text{ }\mathrm{Hz}$) with respect to that of binaries with convex (regular) dynamics. Similar shifts have been reported in the literature, attributed however to first-order phase transitions from $\mathrm{nuclear}/\mathrm{hadronic}$ matter to deconfined quark matter. We argue that the ultimate origin of the frequency shifts is to be found in the presence of anomalous, nonconvex dynamics in the binary remnant.