# Effects of LESA in Three-Dimensional Supernova Simulations with Multi-Dimensional and Ray-by-Ray-plus Neutrino Transport

**Authors:** Robert Glas, H. -Thomas Janka, Tobias Melson, Georg Stockinger, Oliver Just  
**arXiv:** [1809.10150](https://arxiv.org/abs/1809.10150)  
**Date:** 2018-09-26  
**Summary page:** https://www.summarizepaper.com/en/paper/1809.10150v1/

## Key points

- The study evaluates eight self-consistent, time-dependent supernova simulations in three spatial dimensions for 9 solar-mass and 20 solar-mass progenitors.
- The simulations investigate the presence of dipolar asymmetries of the electron lepton-number emission, known as lepton-number emission self-sustained asymmetry (LESA).
- The simulations were performed using the Aenus-Alcar neutrino/hydrodynamics code, which treats the energy- and velocity-dependent transport of neutrinos of all flavors by a two-moment scheme with algebraic M1 closure.
- In all 3D models, substantial dipole amplitudes of the lepton number flux are observed with stable or slowly time evolving direction and overall properties fully consistent with LESA.
- Models with ray-by-ray-plus (RbR+) transport develop LESA dipoles somewhat faster and with temporarily higher amplitudes compared to fully multi-dimensional (FMD) calculations that exhibit cleaner hemispheric asymmetries with a far more dominant dipole.
- RbR+ results display much wider multipole spectra of the neutrino emission anisotropies with significant power also in quadrupole and higher order modes.
- LESA is not a numerical artifact of RbR+ transport.
- The authors discuss LESA as a consequence of a dipolar convection flow inside the nascent neutron star and establish tentatively a connection to Chandrasekhar's linear theory of thermal instability in spherical shells.
- This study provides new insights into the complex mechanisms that drive supernova explosions and highlights the importance of considering multi dimensional neutrino transport in simulations.

## Summary

This study evaluates a set of eight self-consistent, time-dependent supernova simulations in three spatial dimensions for 9 solar-mass and 20 solar-mass progenitors to investigate the presence of dipolar asymmetries of the electron lepton-number emission. The phenomenon, termed lepton-number emission self-sustained asymmetry (LESA), was discovered by Tamborra et al. The simulations were performed using the Aenus-Alcar neutrino/hydrodynamics code, which treats the energy- and velocity-dependent transport of neutrinos of all flavors by a two-moment scheme with algebraic M1 closure. For each progenitor, results with fully multi-dimensional (FMD) neutrino transport and with ray-by-ray-plus (RbR+) approximation are considered for two different grid resolutions. While the 9 solar mass models develop explosions, the 20 solar mass progenitor does not explode with the employed version of simplified neutrino opacities. In all 3D models, substantial dipole amplitudes of the lepton number flux are observed with stable or slowly time evolving direction and overall properties fully consistent with LESA. The study finds that models with RbR+ transport develop LESA dipoles somewhat faster and with temporarily higher amplitudes compared to FMD calculations that exhibit cleaner hemispheric asymmetries with a far more dominant dipole. However, RbR+ results display much wider multipole spectra of the neutrino emission anisotropies with significant power also in quadrupole and higher order modes. These results disprove speculations that LESA is a numerical artifact of RbR+ transport. The authors also discuss LESA as a consequence of a dipolar convection flow inside the nascent neutron star and establish tentatively a connection to Chandrasekhar's linear theory of thermal instability in spherical shells. Overall, this study provides new insights into the complex mechanisms that drive supernova explosions and highlights the importance of considering multi dimensional neutrino transport in simulations.