Shoichi Yamada
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View article: Laplace–Fourier Linear Stability Analysis of Non-relativistic Magnetized Rotational Jets: Mode Identification by Hamiltonian Analysis and the Occurrence of Mode Transitions
Laplace–Fourier Linear Stability Analysis of Non-relativistic Magnetized Rotational Jets: Mode Identification by Hamiltonian Analysis and the Occurrence of Mode Transitions Open
In this paper, we conduct a linear stability analysis of magnetized and/or rotating jets propagating in ambient matter that is also magnetized and/or rotating, having in mind the application to the jet penetrating the core/envelope of a ma…
View article: Asymmetric emissions of neutrinos in the cooling of rotating protoneutron stars
Asymmetric emissions of neutrinos in the cooling of rotating protoneutron stars Open
We evaluate global asymmetry in the luminosities of neutrinos emitted from rapidly rotating protoneutron stars (PNSs). We build axisymmetric models of PNSs in mechanical equilibrium with rotation by adding prescribed angular momentum distr…
View article: Dynamical equilibria of fast neutrino flavor conversion
Dynamical equilibria of fast neutrino flavor conversion Open
Dense neutrino systems, which display collectivity mediated by the weak interaction, have deep parallels with mean-field kinetic systems governed by other fundamental forces. We identify analogues in fast flavor conversion (FFC) of some ti…
View article: Laplace-Fourier linear stability analysis of non-relativistic magnetized rotational jets: mode identification by Hamiltonian analysis and the occurrence of mode transitions
Laplace-Fourier linear stability analysis of non-relativistic magnetized rotational jets: mode identification by Hamiltonian analysis and the occurrence of mode transitions Open
In this paper, we conduct a linear stability analysis of magnetized and/or rotating jets propagating in ambient matter that is also magnetized and/or rotating, having in mind the application to the jet penetrating the core/envelope of a ma…
View article: Comparative testing of subgrid models for fast neutrino flavor conversions in core-collapse supernova simulations
Comparative testing of subgrid models for fast neutrino flavor conversions in core-collapse supernova simulations Open
We investigate key methodologies of Bhatnagar-Gross-Krook subgrid modeling for neutrino fast flavor conversions (FFC) in core-collapse supernova based on spherically symmetric Boltzmann radiation hydrodynamics simulations. We first examine…
View article: Asymmetric emissions of neutrinos in the cooling of rotating proto-neutron stars
Asymmetric emissions of neutrinos in the cooling of rotating proto-neutron stars Open
We evaluate global asymmetry in the luminosities of neutrinos emitted from rapidly-rotating proto-neutron stars (PNS's). We build axisymmetric models of PNS's in mechanical equilibrium with rotation by adding prescribed angular momentum di…
View article: An Extended Closure Relation by LightGBM for Neutrino Radiation Transport in Core-collapse Supernovae
An Extended Closure Relation by LightGBM for Neutrino Radiation Transport in Core-collapse Supernovae Open
We developed a machine learning model using LightGBM, one of the most popular gradient-boosting decision tree methods these days, to predict the Eddington tensor, or the second-order angular moment, for neutrino radiation transport in core…
View article: Quasi-steady evolution of fast neutrino-flavor conversions
Quasi-steady evolution of fast neutrino-flavor conversions Open
In astrophysical environments such as core-collapse supernovae (CCSNe) and binary neutron star mergers (BNSMs), neutrinos potentially experience substantial flavor mixing due to the refractive effects of neutrino self-interactions. Determi…
View article: An Extended Closure Relation by LightGBM for Neutrino Radiation Transport in Core-collapse Supernovae
An Extended Closure Relation by LightGBM for Neutrino Radiation Transport in Core-collapse Supernovae Open
We developed a machine learning model using LightGBM, one of the most popular gradient-boosting decision tree methods these days, to predict the Eddington tensor, or the second-order angular moment, for neutrino radiation transport in core…
View article: Muon-induced collisional flavor instability in core-collapse supernova
Muon-induced collisional flavor instability in core-collapse supernova Open
Neutrinos are known to undergo flavor conversion among their three flavors. In the theoretical modeling of core-collapse supernova, there has been a great deal of attention to recent discoveries of a new type of neutrino flavor conversions…
View article: Physical mechanism of core-collapse supernovae that neutrinos drive
Physical mechanism of core-collapse supernovae that neutrinos drive Open
The current understanding of the mechanism of core-collapse supernovae (CCSNe), one of the most energetic events in the universe associated with the death of massive stars and the main formation channel of compact objects such as neutron s…
View article: Collisional and Fast Neutrino Flavor Instabilities in Two-dimensional Core-collapse Supernova Simulation with Boltzmann Neutrino Transport
Collisional and Fast Neutrino Flavor Instabilities in Two-dimensional Core-collapse Supernova Simulation with Boltzmann Neutrino Transport Open
We present a comprehensive study on the occurrences of the collisional flavor instability (CFI) and the fast flavor instability (FFI) of neutrinos based on a two-dimensional (2D) core-collapse supernova (CCSN) simulation performed with a B…
View article: Universality of the Neutrino Collisional Flavor Instability in Core Collapse Supernovae
Universality of the Neutrino Collisional Flavor Instability in Core Collapse Supernovae Open
Neutrinos are known to undergo flavor conversion processes among the three flavors. The fast flavor conversion (FFC) has been the central piece of flavor conversions taking place in core-collapse supernovae (CCSNe) due to its shorter times…
View article: Systematic study of the resonancelike structure in the collisional flavor instability of neutrinos
Systematic study of the resonancelike structure in the collisional flavor instability of neutrinos Open
Investigations on the resonancelike phenomenon in the collisional flavor instability (CFI) of neutrinos, which were observed in the linear phase recently, are reported. We show that it occurs not only for the isotropy-preserving modes as p…
View article: Quantum mechanical calculations of synchro-curvature radiations: maser possibility
Quantum mechanical calculations of synchro-curvature radiations: maser possibility Open
We calculate the radiative transition rates for synchro-curvature radiation to explore the possibility of maser in the environment that may occur in the magnetosphere of neutron stars (NSs). Unlike previous studies, we employ relativistic …
View article: A Lagrangian construction of rotating star models
A Lagrangian construction of rotating star models Open
We present a new formulation for numerically obtaining axisymmetric equilibrium structures of rotating stars in two spatial dimensions. With a view to apply it to the secular evolution of rotating stars, we base it on the Lagrangian descri…
View article: A Systematic Study on the Resonance in Collisional Neutrino Flavor Instability
A Systematic Study on the Resonance in Collisional Neutrino Flavor Instability Open
Investigations on the resonance in the collisional flavor instability (CFI) of neutrinos, which were reported recently, are reported. We show that the resonance occurs not only for the isotropy-preserving modes as pointed out in the previo…
View article: Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation Hydrodynamics Code
Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation Hydrodynamics Code Open
We investigate protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a snapsho…
View article: A novel Lagrangian formulation to construct relativistic rotating stars: towards its application to their evolution calculations
A novel Lagrangian formulation to construct relativistic rotating stars: towards its application to their evolution calculations Open
We present a new formulation to construct numerically equilibrium configurations of rotating stars in general relativity. Having in mind the application to their quasi-static evolutions on a secular time-scale, we adopt a Lagrangian formul…
View article: A Lagrangian construction of rotating stars
A Lagrangian construction of rotating stars Open
We present a new formulation for numerically obtaining axisymmetric equilibrium structures of rotating stars in two spatial dimensions. With a view to apply it to the secular evolution of rotating stars, we base it on the Lagrangian descri…
View article: Leptonic and semi-leptonic neutrino interactions with muons in proto-neutron star cooling
Leptonic and semi-leptonic neutrino interactions with muons in proto-neutron star cooling Open
It is known that muons are scarce just after the birth of a proto-neutron star via a supernova explosion, but get more abundant as the proto-neutron star cools via neutrino emissions on the Kelvin–Helmholtz timescale. We evaluate all the r…
View article: Principal-axis Analysis of the Eddington Tensor for the Early Post-bounce Phase of Rotational Core-collapse Supernovae
Principal-axis Analysis of the Eddington Tensor for the Early Post-bounce Phase of Rotational Core-collapse Supernovae Open
Using full Boltzmann neutrino transport, we performed 2D core-collapse supernova simulations in axisymmetry for two progenitor models with 11.2 and 15.0 M ⊙ , both rotational and nonrotational. We employed the results obtained in the early…
View article: Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation-Hydrodynamics Code
Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation-Hydrodynamics Code Open
We investigate the protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation-hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a sna…
View article: A novel formulation for the evolution of relativistic rotating stars
A novel formulation for the evolution of relativistic rotating stars Open
We present a new formulation to construct numerically equilibrium configurations of rotating stars in general relativity. Having in mind the application to their quasi static evolutions, we adopt a Lagrangian formulation of our own devisin…
View article: Singularity-Avoiding Multi-Dimensional Root-Finder
Singularity-Avoiding Multi-Dimensional Root-Finder Open
We proposed in this paper a new method, which we named the W4 method, to solve nonlinear equation systems. It may be regarded as an extension of the Newton-Raphson~(NR) method to be used when the method fails. Indeed our method can be appl…
View article: Deep Learning of the Eddington Tensor in Core-collapse Supernova Simulation
Deep Learning of the Eddington Tensor in Core-collapse Supernova Simulation Open
We trained deep neural networks (DNNs) as a function of the neutrino energy density, flux, and the fluid velocity to reproduce the Eddington tensor for neutrinos obtained in our first-principles core-collapse supernova simulation. Although…
View article: Quantum synchro-curvature masers and their application to neutron stars
Quantum synchro-curvature masers and their application to neutron stars Open
We explore the possibility of synchro-curvature maser in the magnetosphere of neutron stars (NSs). Unlike previous studies, we employ relativistic quantum mechanics, solving the Dirac equation for an electron in helical magnetic fields and…
View article: Stellar Core-collapse Simulations with the Boltzmann-radiation-hydrodynamics Code under Axisymmetry
Stellar Core-collapse Simulations with the Boltzmann-radiation-hydrodynamics Code under Axisymmetry Open
We report the stellar core-collapse simulations of the 11.2 \(M_{ \odot }\) progenitor under axisymmetry with varying the nuclear equations of state (EOSs) and the rotational velocities by using the Boltzmann-radiation-hydrodynamics code. …