Weak magnetism for antineutrinos in supernovae

Abstract

Weak magnetism increases antineutrino mean free paths in core collapse supernovae. The parity violating interference between axial and vector currents makes antineutrino-nucleon cross sections smaller then those for neutrinos. We calculate simple, exact correction factors to include recoil and weak magnetism in supernova simulations. Weak magnetism may significantly increase the neutrino energy flux. We calculate, in a diffusion approximation, an increase of order 15% in the total energy flux for temperatures near 10 MeV. This should raise the neutrino luminosity. Weak magnetism also changes the emitted spectrum ofνx (with x = µ or τ ) andνe. We estimate thatνx will be emitted about 7% hotter than νx becauseνx have longer mean free paths. Likewise weak magnetism may increase theνe temperature by of order 10%. This increase in temperature coupled with the increase in neutrino luminosity should increase the heating in the low density region outside of the neutrino sphere. This, in turn, could be important for the success of an explosion. It is important to check our results with a full simulation that includes Boltzmann neutrino transport and weak magnetism corrections.

The role of weak interactions in dynamic ejecta from binary neutron star mergers

“…The distribution functions of electrons and positrons, f e ∓ , are assumed to obey FermiDirac distributions with non-vanishing chemical potentials. The electron mass correction term is M(x) = 1 − (m e /x) 2 1/2 , while the weak magnetism factors, R νe,νe , are implemented according to Horowitz (2002). Their detailed expressions are provided in Appendix A. Free-streaming neutrinos and antineutrinos are assumed to be described by a distribution function with a Fermi-Dirac energy spectrum of temperature T ν and zero degeneracy, and with an angular dependence g ν ,…”

“…(19)−(22), we employ the weak magnetism and recoil corrections provided by Horowitz (2002) for charged current reactions on free nucleons:…”

Neutrino-Nucleon Interactions in Supernova: Hartree Response & Approximations

“…However, at densities around 10 12 g cm −3 and temperatures above 10 MeV differences on the order of 10% appear between the two [13]. For nonrelativistic opacities with recoil such as in [10], a specific correction factor, based on the corresponding vacuum cross sections in [11], was deduced in [14] and included in the neutrino transport code VERTEX. Fig.…”

“…To remove some of the deficiencies regarding the simplifications of the matrix element, analytic correction factors for neutrino opacities were proposed and later implemented in supernova simulations. Essentially, these factors are the ratio of the free space cross section, corresponding to the Hartree response of a free nucleon initially at rest, over the cross section corresponding to the opacity with the respective simplifications [11].…”

Production of56Ni in black hole-neutron star merger accretion disc outflows

“…where b = 9.704 × 10 −50 cm 2 ·keV −2 , m e is the electron mass, ∆ is the neutron-proton mass difference, W M = 1+1.1(E/m n ) and WM = 1−7.1(E/m n ) are the weak magnetism corrections [33] and φ eff ν , φ ef ν are the effective neutrino and antineutrino fluxes in units of 1/(cm 2 ·s·keV). The effective neutrino and antineutrino fluxes as observed by the outflowing fluid element above each disk snapshot are calculated as in [24].…”