Electron-neutrino lepton number crossings: Variations with the supernova core physics

TL;DR

This study investigates how different supernova core physics, including microphysics and convection, influence the electron-neutrino lepton number crossings, which are crucial for understanding neutrino flavor conversions in supernovae.

Contribution

It provides a detailed analysis of how various microphysical processes and convection affect ELN crossings in supernova simulations, highlighting their subtle impacts.

Findings

Proto-neutron star convection shifts the star's radius outward, promoting ELN crossings at larger radii.

Muon creation leads to proto-neutron star contraction, facilitating ELN crossings at smaller radii.

Effects of microphysics on ELN crossings are mild and depend on the nuclear equation of state.

Abstract

A crucial ingredient affecting fast neutrino flavor conversion in core-collapse supernovae (SNe) is the shape of the angular distribution of the electron-neutrino lepton number (ELN). The presence of an ELN crossing signals favorable conditions for flavor conversion. However, the dependence of ELN crossings on the SN properties is only partially understood. We investigate a suite of 12 spherically symmetric neutrino-hydrodynamics simulations of the core collapse of a SN with a mass of $18.6 M_\odot$; each model employs different microphysics (i.e., three different nuclear equations of state, with and without muon creation) and includes or not a mixing-length treatment for proto-neutron star convection. We solve the Boltzmann equations to compute the neutrino angular distributions relying on static fluid properties extracted from each of the SN simulations in our suite for six selected post-bounce times. We explore the dependence of the ELN distributions on the SN microphysics and proto-neutron star convection. We find that the latter shifts the proto-neutron star radius outwards, favoring the appearance of ELN crossings at larger radii. On the other hand, muon creation causes proto-neutron star contraction, facilitating the occurrence of ELN crossings at smaller radii. These effects mildly depend on the nuclear equation of state. Our findings highlight the subtle impact of the SN microphysics, proto-neutron star convection, and neutrino transport on the ELN angular distributions.