arXiv subjects

Kohsuke Sumiyoshi

Publications and source records attributed to Kohsuke Sumiyoshi.

At least 19 recordsLinked to original sources

arXiv2026

Influence of effective mass of the relativistic mean field theory on core collapse supernovae and compact objects

We study the influence of the effective mass in the relativistic mean field (RMF) theory on the properties of the central core of collapse-driven supernovae and the formation of compact objects. Influence of the effective mass has been so far studied within the non-relativistic frameworks. In order to clarify the role of the effective mass in the relativistic frameworks, which is different from non-relativistic ones, we adopt the set of equation of state (EOS) tables using the parameterizations TM1e and TM1m, which have different effective masses but with the same saturation properties, in the RMF theory. We show that choices of the effective mass in supernova matter affect both the stiffness of the EOS through pressure and the thermodynamical behavior through temperature under the RMF frameworks. We explore differences in matter evolution with neutrino emissions by performing a set of numerical simulations of the gravitational collapse and bounce of massive stars and the cooling of the proto-neutron stars. The EOS with large effective mass leads to compact proto-neutron stars and early collapse to black holes with high densities and temperatures due to the softness. It leads to high energy neutrinos in long emission from the proto-neutron star cooling and in short burst from the black hole formation.

astro-ph.HE↗

arXiv2026

Bifurcated Impact of Neutrino Fast Flavor Conversion on Core-collapse Supernovae Informed by Multi-angle Neutrino Radiation Hydrodynamics

In this {\it Letter}, we present a compelling and robust argument for the roles of neutrino fast flavor conversion (FFC) in the explosion mechanism of core-collapse supernova (CCSN), combining the {\it multi-angle} FFC subgrid model rooted in quantum kinetic theory with the multi-dimensional four-species Boltzmann neutrino radiation hydrodynamics. Employing various progenitor masses and the nuclear equations of states, we find that the effect of FFC on CCSN explosion is bifurcated depending on the progenitors. For the lowest-mass progenitor, FFC facilitates the shock revival and enhances the explosion energy, whereas for higher-mass progenitors its impact is inhibitory. We identify the mass accretion rate as the key determinant governing this bifurcation. When the mass accretion rate is low (high), the contribution of FFC to neutrino heating becomes positive (negative), because the heating efficiency enhancement via FFC-driven spectral hardening of electron-type neutrinos dominates over (is outweighed by) the concurrent reduction in neutrino luminosity. Our results further highlight the limitations of approximate neutrino transport, and demonstrate that a multi-angle treatment is essential for accurately capturing FFC effects; otherwise, FFCs are missed and even generated spuriously.

astro-ph.HE↗

arXiv2026

Impact of Effective Nucleon Mass and Multineutron States on the Equation of State for Core-Collapse Supernovae

In this study, we investigate the impact of effective nucleon mass and the existence of the dineutron $(\mathrm{^{2}n})$ and the tetraneutron $(\mathrm{^{4}n})$ on the thermodynamic properties and nuclear compositions by constructing new equations of state. Our results indicate that the model with a larger effective nucleon mass slightly alters the nuclear composition in neutron-rich environments primarily due to differences in the symmetry energy: the mass fractions of unbound neutrons, protons, and heavy nuclei increase. The impact on the thermodynamic properties is negligible, except for the chemical potentials. On the other hand, multineutron states become prominent at high densities in neutron-rich environments, leading to a substantial reduction in the unbound neutron fraction. This depletion lowers the chemical potential of unbound neutrons, which in turn reduces the abundance of neutron-rich nuclei. Consequently, the number of unbound protons increases, leading to a corresponding rise in proton chemical potential. These shifts in chemical potentials promote the formation of heavy nuclei with larger mass and atomic numbers. Ultimately, this compositional shift results in a lower free energy, primarily driven by the emergence of these heavy nuclei.

nucl-th↗

arXiv2025

Neutrino Constraints on Black Hole Formation in M31

We investigate neutrino signals associated with black hole formation resulting from the gravitational collapse of massive stars, motivated by the candidate failed supernova M31-2014-DS1 in the Andromeda Galaxy (M31). By compiling numerical simulation results for stellar collapse, we predict the expected neutrino emission and compare these predictions with observational limits from Super-Kamiokande (SK). The simulations reveal a characteristic precursor signal consisting of a short, intense burst whose average neutrino energy rises rapidly and then ceases abruptly once the black hole forms. We examine several nuclear equations of state, specifically the Lattimer \& Swesty, Shen, Togashi, and SFHo models, to evaluate how the emission depends on neutron-star properties and nuclear-physics uncertainties. Comparison of the predicted event counts with SK's non-detection of neutrinos coincident with M31-2014-DS1 already rules out part of the model space and highlights the sensitivity of current neutrino detectors to both progenitor mass and the EOS. These findings demonstrate the capability of neutrino astronomy to probe core collapse and black hole formation in failed supernova scenarios.

astro-ph.HE↗

arXiv2025

Role of symmetry energy at subnuclear densities in protoneutron star crusts

The impact of matter properties at subnuclear densities on the evolution of protoneutron stars is investigated. Several models of nuclear equation of state (EOS) are constructed with varying saturation parameters, particularly the symmetry energy $S_0$ and its density slope $L$. Using the Thomas--Fermi approximation, the mass and proton numbers of heavy nuclei at subnuclear densities are systematically evaluated, along with their dependence on the EOS. Cooling simulations of protoneutron stars reveal that EOSs with smaller $L$ values lead to a longer cooling timescale and higher average neutrino energies. This behavior is attributed to the enhanced neutrino scattering caused by larger mass numbers, which increases the thermal insulation. Furthermore, the crystallization temperature, marking the onset of crust formation, is found to be higher for EOSs with smaller values of $L$. This is due to the enhanced Coulomb energy associated with larger proton numbers. As a result, despite slower cooling, crust formation occurs earlier for smaller-$L$ EOSs. These findings indicate that the timing of crust formation is sensitive to the EOS and highlight the importance of late-time neutrino observations as probes of the matter properties at subnuclear densities.

astro-ph.HE↗

arXiv2025

Observing Supernova Neutrino Light Curves with Super-Kamiokande.VI. A Practical Data Analysis Technique Considering Realistic Experimental Backgrounds

Neutrinos from supernovae, especially those emitted during the late phase of core collapse, are essential for understanding the final stages of massive star evolution. We have been dedicated to developing methods for the analysis of neutrinos emitted during the late phase and observed at Super-Kamiokande (SK). Our previous studies have successfully demonstrated the potential of various analysis methods in extracting essential physical properties; however, the lack of background consideration has limited their practical application. In this study, we address this issue by incorporating a realistic treatment of the experimental signal and background events with the on-going SK experiment. We therefore optimize our analysis framework to reflect realistic observational conditions, including both signal and background events. Using this framework we study several long-time supernova models, simulating the late phase neutrino observation in SK and focusing in particular on the identification of the last observed event. We discuss the possibility of model discrimination methods using timing information from this last observed event.

astro-ph.HE↗

arXiv2025

Neutrino flavor instabilities in a binary neutron star merger remnant: Roles of a long-lived hypermassive neutron star

Understanding the post-merger evolution of binary neutron star merger (BNSM) requires accurate modeling of neutrino transport and microphysics including neutrino flavor conversions. Many previous studies have suggested that fast flavor instability (FFI) and collisional flavor instability (CFI) pervade inner regions of BNSM remnant, and they could impact on fluid dynamics and r-process nucleosynthesis. In this work, we re-examine prospects of occurrences of FFI and CFI using Boltzmann neutrino transport, assuming a frozen fluid background obtained from a numerical relativity simulation of BNSM. We pay special attention to a case involving a long-lived ($>1\,$ s) hypermassive neutron star (HMNS). Apart from confirming the claim that these flavor instabilities can occur in BNSM remnants, some new insights are revealed. We identify multiple mechanisms responsible for generating electron neutrino lepton number (ELN) angular crossings, corresponding to a key indicator of FFI onset, which differ notably from those in black hole (BH) accretion disk systems. We argue that the appearance of positive chemical potential of electron-type neutrinos plays important roles on generating ELN angular crossings. For CFI, their growth rates are generally lower than FFI, but they can persistently occur in most of the accretion disk up to $\sim 1\,$ s. We also find that neglecting contributions of heavy-leptonic neutrinos results in overestimating growth rate and area of unstable regions of CFI. Our result suggests that FFI (CFI) tends to occur transiently (persistently) and locally (widespread in the disk), and FFI is more sensitive to the central compact object (HMNS or BH) than CFI, though more self-consistent simulations with incorporating effects of flavor conversions are needed to confirm these claims.

astro-ph.HE↗

arXiv2025

Observing Supernova Neutrino Light Curves with Super-Kamiokande. V. Distance Estimation with Neutrinos

Neutrinos are pivotal signals in multi-messenger observations of supernovae (SNe). Recent advancements in the analysis method of supernova (SN) neutrinos, especially in quantitative analysis, have significantly broadened scientific possibilities. This study demonstrates the feasibility of estimating distances to SNe using neutrinos. This estimation utilizes the direct relationship between the radius of a neutron star (NS) and the distance to the SN, which is analogous to main-sequence fitting. The radius of an NS is determined with an approximate uncertainty of 10% through observations such as X-rays and gravitational waves. By integrating this information, the distance to the SN can be estimated with an uncertainty of within 15% at a 95% confidence level. It has been established that neutrinos can pinpoint the direction of SNe, and when combined with distance estimates, three-dimensional localization becomes achievable. This capability is vital for follow-up observations using multi-messenger approaches. Moreover, more precise distance determinations to SNe through follow-up observations, such as optical observations, allow for accurate measurements of NS radii. This data, via the NS mass-radius relationship, could provide various insights into nuclear physics.

astro-ph.HE↗

arXiv2025

Influence of effective nucleon mass on equation of state for supernova simulations and neutron stars

We investigate the influence of the effective nucleon mass on the equation of state (EOS), which is constructed for simulations of core-collapse supernovae and binary neutron star mergers, within the relativistic mean-field (RMF) framework. The study introduces a new RMF parameter set, TM1m, which is a modification of the TM1e model with an adjusted effective mass, maintaining the saturation properties of nuclear matter. The TM1m model, with a larger effective mass ratio ($M^{\ast}/M \sim 0.8$) compared to the TM1e model ($M^{\ast}/M \sim 0.63$), is employed to construct a new EOS table, EOS5. This EOS table is designed to offer insights into the influence of the effective nucleon mass on the EOS within a relativistic framework, particularly above the saturation density. The results of EOS5 are compared with those obtained from other models, including both relativistic and nonrelativistic approaches. The properties of cold neutron stars, calculated using the TM1m model, are compatible with the existence of a $2\ M_\odot$ pulsar and the latest constraints on the tidal deformability and radii of a canonical $1.4\ M_\odot$ neutron star, derived from astrophysical observations.

nucl-th↗

arXiv2024

Neutron star kick driven by asymmetric fast-neutrino flavor conversion

Multi-dimensional nature of core-collapse supernova (CCSN) leads to asymmetric matter ejection and neutrino emission, that potentially accounts for the origin of neutron star (NS) kick. Asymmetric neutrino radiation fields are, in general, accompanied by large-scale inhomogeneous fluid distributions, in particular for electron-fraction ($Y_e$) distributions. Recently, it has also been revealed that lower $Y_e$ environments in proto-neutron star envelope can offer preferable conditions for collective neutrino oscillations. In this paper, we show that a dipole asymmetry of fast neutrino-flavor conversion (FFC), one of the collective neutrino oscillation modes, can power a NS kick, and that it would generate a characteristic correlation between asymmetric distributions of heavy elements in the ejecta and the direction of NS kick. We strengthen our argument for the FFC-driven NS kick mechanism by performing axisymmetric neutrino transport simulations with full Boltzmann neutrino transport. We show that this mechanism can generate sufficient linear momentum of neutrinos to account for typical proper motions of NS. Although more detailed studies are necessary, the present study opens a new channel to give a natal NS kick.

astro-ph.HE↗

arXiv2023

Observing Supernova Neutrino Light Curves with Super-Kamiokande. IV. Development of SPECIAL BLEND: a New Public Analysis Code for Supernova Neutrinos

Supernova neutrinos are invaluable signals that offer information about the interior of supernovae. Because a nearby supernova can occur at any time, preparing for future supernova neutrino observation is an urgent task. For the prompt analysis of supernova neutrinos, we have developed a new analysis code, ``Supernova Parameter Estimation Code based on Insight on Analytic Late-time Burst Light curve at Earth Neutrino Detector (SPECIAL BLEND)''. This code estimates the parameters of supernova based on an analytic model of supernova neutrinos from the proto-neutron star cooling phase. For easy availability to the community, this code is public and easily runs on web environments. SPECIAL BLEND can estimate the parameters better than the analysis pipeline we developed in the previous paper. By using SPECIAL BLEND, we can estimate the supernova parameters within $10\%$ precision up to $\sim 20\,{\rm kpc}$ and $\sim 60\,{\rm kpc}$ (Large Magellanic Cloud contained) with Super Kamiokande and Hyper Kamiokande, respectively.

astro-ph.HE↗

arXiv2023

Impact of late-time neutrino emission on the diffuse supernova neutrino background

In the absence of high-statistics supernova neutrino measurements, estimates of the diffuse supernova neutrino background (DSNB) hinge on the precision of simulations of core-collapse supernovae. Understanding the cooling phase of protoneutron star (PNS) evolution ($\gtrsim1\,{\rm s}$ after core bounce) is crucial, since approximately 50% of the energy liberated by neutrinos is emitted during the cooling phase. We model the cooling phase with a hybrid method by combining the neutrino emission predicted by 3D hydrodynamic simulations with several cooling-phase estimates, including a novel two-parameter correlation depending on the final baryonic PNS mass and the time of shock revival. We find that the predicted DSNB event rate at Super-Kamiokande can vary by a factor of $\sim2-3$ depending on the cooling-phase treatment. We also find that except for one cooling estimate, the range in predicted DSNB events is largely driven by the uncertainty in the neutrino mean energy. With a good understanding of the late-time neutrino emission, more precise DSNB estimates can be made for the next generation of DSNB searches.

astro-ph.HE↗

arXiv2022

Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation-Hydrodynamics Code

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 snapshot of a PNS at 2.3 seconds after bounce from a 1D PNS cooling calculation and run our simulation for $\sim160\,\mathrm{ms}$ in 2D under axisymmetry. The original PNS cooling calculation neglected convection entirely and the initial condition is linearly unstable to convection. We find in our 2D simulation that convection is instigated there indeed and expands inward after being full-fledged. The convection is then settled to a quasi-steady state in $\sim100\,\mathrm{ms}$, being sustained by the negative $Y_e$ gradient, which is in turn maintained by neutrino emissions. It enhances the luminosities and mean energies of all species of neutrinos compared to 1D. Taking advantage of the Boltzmann solver, we analyze the possible occurrence of the neutrino fast flavor conversion (FFC). We found that FFC is likely to occur in the regions, where $Y_e$ is lower, and that the growth rate can be as high as $\sim 10^{-1}\,{\mathrm{cm}^{-1}}$.

astro-ph.HE↗

arXiv2022

Effects of nuclear matter and composition in core-collapse supernovae and long-term proto-neutron star cooling

We study the influence of hot and dense matter in core-collapse supernovae by adopting up-to-date nuclear equation of state (EOS) based on the microscopic nuclear many-body frameworks. We explore effects of EOS based on the Dirac Brueckner Hartree-Fock theory through comparisons with those based on the variational method. We also examine effects of the differences in the composition of nuclei and nucleons by using the same EOS by the variational method but employing two different treatments in computations of nuclear abundances. We perform numerical simulations of core-collapse supernovae adopting the three EOSs. We also perform numerical simulations of the long-term evolution over 70 s of the proto-neutron star cooling. We show that impacts by different modeling of composition are remarkable as in those by different treatments of uniform matter in the gravitational collapse, bounce, and shock propagation. The cooling of proto-neutron star and the resulting neutrino emission are also affected by the compositional difference even if the same treatment in computing uniform matter of EOS.

astro-ph.HE↗

arXiv2022

Leptonic and semi-leptonic neutrino interactions with muons in the proto-neutron star cooling

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. In this paper we evaluate all the relevant rates of the neutrino interactions with muons at different times in the proto-neutron star cooling. We are particularly interested in the late phase ($ t \gtrsim 10 \operatorname{s}$), which will be accessible in the next Galactic supernova but has not been studied well so far. We calculate both leptonic and semi-leptonic processes, for the latter of which we pay attention also to the form factors with their dependence on the transferred momentum as well as to the modification of the dispersion relations for nucleons on the mean field level. We find that the flavor-exchange reactions $ν_e + μ^- \rightarrow ν_μ + e^-$ and $\barν_μ + μ^- \rightarrow \barν_e + e^-$ can be dominant, particularly at low energies, over the capture of $ν_e$ on neutron and the scatterings of $\barν_μ$ on nucleons as the opacity sources for these species and that the inverse muon decay $ \barν_e + ν_μ + e^- \leftrightarrows μ^- $ can overwhelm the scatterings of $\barν_e$ and $ν_μ$ on nucleons again at low energies. At high energies, on the other hand, the corrections in the semi-leptonic processes mentioned above are more important. We also show the non-trivial energy- and angular dependences of the flavor-exchange reactions and the inverse muon decay. In the study of the diffusion coefficients from these reactions, we find that $\barν_μ$ is most affected. These pieces of information are indispensable for numerical computations and the interpretation of results thereof for the proto-neutron star cooling particularly at the very late phase.

astro-ph.HE↗

arXiv2022

Stability analysis of supermassive primordial stars: a new mass range for general relativistic instability supernovae

Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the direct collapse of a supermassive star, has several possible probes including the explosion of a helium-core supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution code. This method is more accurate than previous determinations and it finds that the instability occurs earlier in the evolutionary life of the star. Using the results of the stability analysis, we perform 1D general relativistic hydrodynamical simulations and we find two general relativistic instability supernovae fueled by alpha capture reactions as well as several lower mass pulsations, analogous to the puslational pair instability process. The mass range for the events (2.6-3.0 $\times 10^4$ ${\rm M}_\odot$) is lower than had been suggested by previous works (5.5 $\times 10^4$ ${\rm M}_\odot$) because the instability occurs earlier in the star's evolution. The explosion may be visible to, among others, JWST, while the discovery of the pulsations opens up additional possibilities for observation.

astro-ph.SR↗

arXiv2022

Equation of state in neutron stars and supernovae

Neutron stars and supernovae provide cosmic laboratories of highly compressed matter at supra nuclear saturation density which is beyond the reach of terrestrial experiments. The properties of dense matter is extracted by combining the knowledge of nuclear experiments and astrophysical observations via theoretical frameworks. A matter in neutron stars is neutron rich, and may further accommodate non-nucleonic degrees of freedom such as hyperons and quarks. The structure and composition of neutron stars are determined by equations of state of matter, which are the primary subject in this chapter. In case of supernovae, the time evolution includes several dynamical stages whose descriptions require equations of state at finite temperature and various lepton fractions. Equations of state also play essential roles in neutron star mergers which allow us to explore new conditions of matter not achievable in static neutron stars and supernovae. Several types of hadron-to-quark transitions, from first order transitions to crossover, are reviewed, and their characteristics are summarized.

nucl-th↗

arXiv2022

Principal-Axis Analysis of the Eddington Tensor for the Early Post-Bounce Phase of Rotational Core-Collapse Supernovae

Using full Boltzmann neutrino transport, we performed two-dimensional (2D) core-collapse supernova simulations in axisymmetry for two progenitor models with 11.2M and 15.0M both rotational and non-rotational. We employed the results obtained in the early post-bounce phase (t < 20 ms) to assess performance under rapid rotation of some closure relations commonly employed in the truncated moment method. We first made a comparison in 1D under spherical symmetry, though, of the Eddington factor p defined in the fluid rest frame (FR). We confirmed that the maximum entropy closure for the Fermionic distribution (MEFD) performs better than others near the proto-neutron star surface, where p < 1/3 occurs, but does not work well even in 1D when the phase space occupancy satisfies e < 0.5 together with p < 1/3, the condition known to be not represented by MEFD. For the 2D models with the rapid rotation, we employed the principal-axis analysis of the Eddington tensor. We paid particular attention to the direction of the longest principal axis. We observed in FR that it is aligned neither with the radial direction nor with the neutrino flux in 2D, particularly so in convective and/or rapidly rotating regions, the fact not accommodated in the moment method. We repeated the same analysis in the laboratory frame (LB) and found again that the direction of the longest principal axis is not well reproduced by MEFD because the interpolation between the optically thick and thin limits is not very accurate in this frame.

astro-ph.HE↗