Electron Capture and Its Reverse Process in Hot and Dense Astronuclear Matter

Abstract

Electron capture rate, e-neutrino absorption rate, and e-neutrino absorption mean free path in hot and dense astronuclear matter are calculated in the framework of relativistic mean field (RMF) theory. Their dependence on the density, temperature, and the neutrino abundance of the matter is investigated. We find that the electron capture rate and the neutrino absorption rate are proportional to the cube of the value of the temperature as e-neutrinos are trapped in the stellar matter, and the e-neutrino absorption mean free path is proportional to the inverse of the square of the temperature. The reaction rates increase with the density and the neutrino abundance of the matter. Exact calculation of the reaction rates and the neutrino absorption mean free path is compared with that utilizing the degeneracy approximation. It shows that the latter is inappropriate under the following circumstances: when the stellar matter has a low neutrino abundance, when the density is about or less than the nuclear saturation density, and when the temperature of the matter has a relatively high value, being of the order of 10 MeV or even higher. Kinematically suppressed electron capture or neutrino absorption can be reopened by increasing the temperature of the matter, and its threshold value is about several MeVs when the density of the stellar matter is around the nuclear saturation density. We also discuss the case which is out of beta equilibrium, and the relaxation timescale is estimated. In addition, we show that the strong interactions manifested by the RMF theory decrease the electron capture rate and enlarge the neutrino mean free path if the neutrinos are trapped.

Damping of density oscillations in neutrino-transparent nuclear matter

“…For the mass m i , we use the rest mass in vacuum. The microscopic origin of the nuclear mean field can be understood through the framework of relativistic mean field theories, where the mean field U is a function of the vacuum expectation values of the ω and ρ mesons which are the strong force carriers between nucleons [41]. As alluded to in Sec.…”

“…In the rate calculations (3) and (4), E * should be used for the energies in the matrix element and in the energy factors in the denominator, while E should be used in the energy delta function and the Fermi Dirac factors [15,41,42]. However, in the approximation we used for the direct Urca matrix element (7), the E * factors cancel out.…”

Beta Equilibrium under Neutron Star Merger Conditions

“…Refs. [8][9][10][11] calculate the neutrino mean free path using a fully relativistic formalism, while integrating over the full phase space. Ref.…”

Distinguishing Newly Born Strange Stars from Neutron Stars withg-Mode Oscillations

“…We take the formalism of the Lagrangian density for RMF as the same as that used in Ref. [28]. Five parameters for the theory are fixed by fitting the properties of the symmetric nuclear matter at saturation density: saturation nucleon number density ρ 0 = 0.16 fm Within the framework of RMF theory, we can obtain the energy density and the pressure of the hot NS matter.…”

“…It is remarkable that, in the interior of a newly born NS, the temperature is of order 10 MeV and the timescale of establishing the beta equilibrium can be smaller than ∼ 10 −8 s [28], which is much smaller than the period of the g-mode pulsations about 10 −3 ∼ 10 −2 s. Therefore, in our calculation we assume that Y L for each fluid element is constant and the system is in beta equilibrium during the process of pulsations, which is consistent with the Ledoux convective criterion in supernova simulations [29]. This situation is different from that in cold NS where beta equilibrium can not be obtained during the pulsations and the electron fraction Y e rather than Y L remains unchanged [22].…”