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Neutrino-matter interactions play a key role in binary neutron star mergers. Thermodynamics conditions at the surfaces where neutrinos decouple from matter influence neutrino spectra, ultimately affecting the evolution of the remnant and the properties of the ejecta. In this work, we post-process results of general relativistic merger simulations employing microphysical equations of state and approximate neutrino transport to investigate the thermodynamics conditions at which weak and thermal equilibrium freezes out (equilibrium surfaces), as well as conditions at which the transition between diffusion and free-streaming regime occurs (diffusion surfaces). We find that the rest mass density and the neutrino energy are the most relevant quantities in determining the location of the decoupling surfaces. For mean energy neutrinos ($langle E_{{ u}_e} rangle approx 9~{rm MeV}$, $langle E_{{bar{ u}}_e} rangle approx 15~{rm MeV}$, $langle E_{{ u}_{mu,tau}} rangle approx 25~{rm MeV}$), diffusion surfaces are located around $10^{11}{rm g~cm^{-3}}$ for all neutrino species, while equilibrium surfaces for heavy flavor neutrinos are significantly deeper (several $10^{12}{rm g~cm^{-3}}$) than the ones of $bar{ u}_e$ and $ u_e$ ($gtrsim 10^{11}{rm g~cm^{-3}}$). The resulting decoupling temperatures are in good agreement with the average neutrino energies ($langle E_{ u} rangle sim 3.15~T$), with the softer equation of state characterized by systematically larger decoupling temperatures ($Delta T lesssim 1~{rm MeV}$). Neutrinos streaming at infinity with different energies come from very different regions of the remnant. The presence of a massive NS or of a BH in the remnant influences the neutrino thermalization process.
In order to extract maximal information from neutron-star merger signals, both gravitational and electromagnetic, we need to ensure that our theoretical models/numerical simulations faithfully represent the extreme physics involved. This involves a r
The detections of gravitational waves (GWs) from binary neutron star (BNS) systems and neutron star--black hole (NSBH) systems provide new insights into dense matter properties in extreme conditions and associated high-energy astrophysical processes.
With the first observation of a binary neutron star merger through gravitational waves and light GW170817, compact binary mergers have now taken the center stage in nuclear astrophysics. They are thought to be one of the main astrophysical sites of p
We present a first exploration of the results of neutron star-black hole mergers using black hole masses in the most likely range of $7M_odot-10M_odot$, a neutrino leakage scheme, and a modeling of the neutron star material through a finite-temperatu
(abridged) We investigate the quark deconfinement phase transition in the context of binary neutron star (BNS) mergers. We employ a new finite-temperature composition-dependent equation of state (EOS) with a first order phase transition between hadro