103 research outputs found
Global features of fast neutrino-flavor conversion in binary neutron star merger
Binary neutron star merger (BNSM) offers an environment where fast
neutrino-flavor conversion (FFC) can vividly occur, that potentially leads to a
considerable change of neutrino radiation field. In this Letter, we investigate
global features of FFC by general relativistic quantum kinetic neutrino
transport simulations in spatial axisymmetry. Our result suggests that global
advection of neutrinos plays a crucial role in FFC dynamics. Although flavor
conversions occur ubiquitously in the early phase, they can be active only in a
narrow region in the late phase. This region includes an ELN-XLN Zero Surface
(EXZS), corresponding to a surface where electron-neutrinos lepton number (ELN)
equals to heavy-leptonic one (XLN). The EXZS is not stationary, but dynamically
evolve in a time scale of global advection. We also find that neutrinos can
undergo a flavor swap when they pass through the EXZS, resulting in
qualitatively different neutrino radiation fields between both sides of EXZS.
Our result suggests that EXZS is one of the key ingredients to characterize FFC
in BNSM.Comment: 6 pages, 5 figure
Roles of fast neutrino-flavor conversion on the neutrino-heating mechanism of core-collapse supernova
One of the greatest uncertainties in any modeling of inner engine of
core-collapse supernova (CCSN) is neutrino flavor conversions driven by
neutrino self-interactions. We carry out large-scale numerical simulations of
multi-energy, multi-angle, three-flavor framework, and general relativistic
quantum kinetic neutrino transport in spherical symmetry with an essential set
of neutrino-matter interactions under a realistic fluid profile of CCSN. Our
result suggests that the neutrino heating in the gain region is reduced by
due to fast neutrino-flavor conversion (FFC). We also find that the
total luminosity of neutrinos is enhanced by , for which the
substantial increase of heavy-leptonic neutrinos by FFCs are mainly
responsible. This study provides evidence that FFC has a significant impact on
the delayed neutrino-heating mechanism.Comment: 6 pages, 3 figure
Critical Surface for Explosions of Rotational Core-Collapse Supernovae
The effect of rotation on the explosion of core-collapse supernovae is
investigated systematically in three-dimensional simulations. In order to
obtain the critical conditions for explosion as a function of mass accretion
rate, neutrino luminosity, and specific angular momentum, rigidly rotating
matter was injected from the outer boundary with an angular momentum, which is
increased every 500 ms. It is found that there is a critical value of the
specific angular momentum, above which the standing shock wave revives, for a
given combination of mass accretion rate and neutrino luminosity, i.e. an
explosion can occur by rotation even if the neutrino luminosity is lower than
the critical value for a given mass accretion rate in non-rotational models.
The coupling of rotation and hydrodynamical instabilities plays an important
role to characterize the dynamics of shock revival for the range of specific
angular momentum that are supposed to be realistic. Contrary to expectations
from past studies, the most rapidly expanding direction of the shock wave is
not aligned with the rotation axis. Being perpendicular to the rotation axis on
average, it can be oriented in various directions. Its dispersion is small when
the spiral mode of the standing accretion shock instability (SASI) governs the
dynamics, while it is large when neutrino-driven convection is dominant. As a
result of the comparison between 2D and 3D rotational models, it is found that
m=!0 modes of neutrino-driven convection or SASI are important for shock
revival around the critical surface.Comment: First revised version, submitted to ApJ, 14 pages, 13 figures, 2
table
Three-dimensional Boltzmann-Hydro code for core-collapse in massive stars I. special relativistic treatments
We propose a novel numerical method for solving multi-dimensional, special
relativistic Boltzmann equations for neutrinos coupled to hydrodynamics
equations. It is meant to be applied to simulations of core-collapse
supernovae. We handle special relativity in a non-conventional way, taking
account of all orders of v/c. Consistent treatment of advection and collision
terms in the Boltzmann equations is the source of difficulties, which we
overcome by employing two different energy grids: Lagrangian remapped and
laboratory fixed grids. We conduct a series of basic tests and perform a
one-dimensional simulation of core-collapse, bounce and shock-stall for a
15M_{sun} progenitor model with a minimum but essential set of microphysics. We
demonstrate in the latter simulation that our new code is capable of handling
all phases in core-collapse supernova. For comparison, a non-relativistic
simulation is also conducted with the same code, and we show that they produce
qualitatively wrong results in neutrino transfer. Finally, we discuss a
possible incorporation of general relativistic effects in our method.Comment: 25 pages, 22 figures, submitted to Ap
Detecting Fast Neutrino Flavor Conversions with Machine Learning
Neutrinos in dense environments like core-collapse supernovae (CCSNe) and
neutron star mergers (NSMs) can undergo fast flavor conversions (FFCs) once the
angular distribution of neutrino lepton number crosses zero along a certain
direction. Recent advancements have demonstrated the effectiveness of machine
learning (ML) in detecting these crossings. In this study, we enhance prior
research in two significant ways. Firstly, we utilize realistic data from CCSN
simulations, where neutrino transport is solved using the full Boltzmann
equation. We evaluate the ML methods' adaptability in a real-world context,
enhancing their robustness. In particular, we demonstrate that when working
with artificial data, simpler models outperform their more complex
counterparts, a noteworthy illustration of the bias-variance tradeoff in the
context of ML. We also explore methods to improve artificial datasets for ML
training. In addition, we extend our ML techniques to detect the crossings in
the heavy-leptonic channels, accommodating scenarios where and
may differ. Our research highlights the extensive versatility and
effectiveness of ML techniques, presenting an unparalleled opportunity to
evaluate the occurrence of FFCs in CCSN and NSM simulations.Comment: Submitted to PR
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