arXiv subjects

Toshitaka Kajino

Publications and source records attributed to Toshitaka Kajino.

At least 37 records · Page 2Linked to original sources

arXiv2023

Effects of Hoyle state de-excitation on $νp$-process nucleosynthesis and Galactic chemical evolution

The partcle-induced hadronic de-excitation of the Hoyle state in $^{12}$C induced by inelastic scattering in a hot and dense plasma can enhance the triple-alpha reaction rate. This prevents the production of heavy nuclei within the neutrino-driven winds of core-collapse supernovae and raises a question as to the contribution of proton-rich neutrino-driven winds as the origin of $p$-nuclei in the solar system abundances. Here we study $νp$-process nucleosynthesis in proton-rich neutrino-driven winds relevant to the production of $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ by considering such particle-induced de-excitation. We show that the enhancement of the triple-alpha reaction rate induced by neutron inelastic scattering hardly affects the $νp$-process, while the proton scattering contributes to the nucleosynthesis in proton-rich neutrino-driven winds at low temperature. The associated enhanced triple-alpha reaction rate decreases the production of $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ in a wind model of ordinary core-collapse supernovae. On the other hand, the abundances of these $p$-nuclei increase in an energetic hypernova wind model. Hence, we calculate the galactic chemical evolution of $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ by taking account of both contributions from core-collapse supernovae and hypernovae. We show that the hypernova $νp$-process can enhance the calculated solar isotopic fractions of $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ and make a significant impact on the GCE of $p$-nuclei regardless of the particle-induced Hoyle state de-excitation.

astro-ph.HE↗

arXiv2023

Underground laboratory JUNA shedding light on stellar nucleosynthesis

Extremely low background experiments to measure key nuclear reaction cross sections of astrophysical interest are conducted at the world's deepest underground laboratory, the Jingping Underground laboratory for Nuclear Astrophysics (JUNA). High precision measurements provide reliable information to understand nucleosynthetic processes in celestial objects and resolve mysteries on the origin of atomic nuclei discovered in the first generations of Pop. III stars in the universe and meteoritic SiC grains in the solar system.

astro-ph.GA↗

arXiv2023

GalCEM I -- An Open-Source Detailed Isotopic Chemical Evolution Code

This is the first of a series of papers that will introduce a user-friendly, detailed, and modular GALactic Chemical Evolution Model, GalCEM, that tracks isotope masses as a function of time in a given galaxy. The list of tracked isotopes automatically adapts to the complete set provided by the input yields. The present iteration of GalCEM tracks 86 elements broken down in 451 isotopes. The prescription includes massive stars, low-to-intermediate mass stars, and Type Ia supernovae as enrichment channels. We have developed a preprocessing tool that extracts multi-dimensional interpolation curves from the input yield tables. These interpolation curves improve the computation speeds of the full convolution integrals, which are computed for each isotope and for each enrichment channel. We map the integrand quantities onto consistent array grids in order to perform the numerical integration at each time step. The differential equation is solved with a fourth-order Runge-Kutta method. We constrain our analysis to the evolution of all the light and intermediate elements from carbon to zinc, and lithium. Our results are consistent up to the extremely metal poor regime with Galactic abundances. We provide tools to track the mass rate change of individual isotopes on a typical spiral galaxy with a final baryonic mass of $5\times 10^{10} M_{\odot}$. Future iterations of the work will extend to the full periodic table by including the enrichment from neutron-capture channels as well as spatially-dependent treatments of galaxy properties. GalCEM is publicly available at https://github.com/egjergo/GalCEM/

astro-ph.GA↗

arXiv2022

Effects of electromagnetic fluctuations in plasmas on solar neutrino fluxes

We explore the effects of electromagnetic (EM) fluctuations in plasmas on solar neutrino fluxes exploiting the fluctuation-dissipation theorem. We find that the EM spectrum in the solar core is enhanced by the EM fluctuations due to the high density of the Sun, which increases the radiation energy density and pressure. By the EM fluctuations involving the modified radiation formula, the central temperature decreases when the central pressure of the Sun is fixed. With a help of the empirical relation between central temperature and neutrino fluxes deduced from the numerical solar models, we present the change in each of the solar neutrino fluxes by the EM fluctuations. We also discuss the enhanced radiation pressure and energy density by the EM fluctuations for other astronomical objects.

astro-ph.SR↗

arXiv2022

Evolution of Urca Pairs in the Crusts of Highly Magnetized Neutron Stars

We report on the effects of strong magnetic fields on neutrino emission in the modified Urca process. We show that the effect of Landau levels on the various Urca pairs affects the neutrino emission spectrum and leads to an angular asymmetry in the neutrino emission. For low magnetic fields the Landau levels have almost no effect on the cooling. However, as the field strength increases, the electron chemical potential increases resulting in a lower density at which Urca pairs can exist. For intermediate field strength there is an interesting interference between the Landau level distribution and the Fermi distribution. For high enough field strength, the entire electron energy spectrum is eventually confined to single Landau level producing dramatic spikes in the emission spectrum.

astro-ph.HE↗

arXiv2022

Comprehensive Analyses of the Neutrino-Process in the Core-collapsing Supernova

We investigate the neutrino flavor change effects due to neutrino self-interaction, shock wave propagation as well as matter effect on the neutrino-process of the core-collapsing supernova (CCSN). For the hydrodynamics, we use two models: a simple thermal bomb model and a specified hydrodynamic model for SN1987A. As a pre-supernova model, we take an updated model adjusted to explain the SN1987A employing recent development of the $(n,γ)$ reaction rates for nuclei near the stability line $(A \sim 100)$. As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and non-equivalent luminosity models. The latter is taken from the synthetic analyses of the CCSN simulation data which involved quantitatively the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated by a shell model for light nuclei and a quasi-particle random phase approximation model for heavy nuclei. For each model, we present abundances of the light nuclei ($^7$Li, $^7$Be, $^{11}$B and $^{11}$C) and heavy nuclei ($^{92}$Nb, $^{98}$Tc, $^{138}$La and $^{180}$Ta) produced by the neutrino-process. The light nuclei abundances turn out to be sensitive to the Mikheyev-Smirnov-Wolfenstein (MSW) region around O-Ne-Mg region while the heavy nuclei are mainly produced prior to the MSW region. Through the detailed analyses, we find that neutrino self-interaction becomes a key ingredient in addition to the MSW effect for understanding the neutrino-process and the relevant nuclear abundances. The normal mass hierarchy is shown to be more compatible with the meteorite data. Main nuclear reactions for each nucleus are also investigated in detail.

nucl-th↗

arXiv2021

Photon vortex generation in quantum level by high-order harmonic synchrotron radiations from spiral moving electrons in magnetic fields

We explore photon vortex generation in synchrotron radiations from a spiral moving electron under a uniform magnetic field along z-axis using Landau quantization. The obtained wave-function of the photon vortecies is the eigen-state of the z-component of the total angular momentum (zTAM). In m-th harmonic radiations, individual photons are the eigen-state of zTAM of m. This is consistent with previous studies. Using the presently obtained wave-functions we calculate the decay widths and the energy spectra under extremely strong magnetic fields of 10^12 - 10^13 G, which are observed in astrophysical objects such as magnetized neutron stars and jets and accretion disks around black holes. The result suggests that photon vortices are predominantly generated in such objects. Although they have no coherency it is expected that photon vortices from the universe are measured using a detector based upon a quantum effect in future. This effect also affects to stellar nucleosynthesis in strong magnetic fields.

astro-ph.HE↗

arXiv2021

A Relativistic Quantum Approach to Neutrino and Antineutrino Emissions via the Direct Urca Process in Strongly Magnetized Neutron-Star Matter

We study neutrino and antineutrino emission from the direct Urca process in neutron-star matter in the presence of strong magnetic fields. We calculate the neutrino emissivity of the direct Urca process, whereby a neutron converts to a proton, an electron and an antineutrino, or a proton-electron pair converts to a neutron-neutrino pair. We solve exact wave functions for protons and electrons in the states described with Landau levels. We find that the direct Urca process can satisfy the kinematic constraints even in density regions where this process could not normally occur in the absence of a magnetic field.

nucl-th↗

arXiv2021

Relativistic Coulomb Screening in Pulsational Pair Instability Supernovae

Context. Pulsational pair-instabilitye supernovae (PPISNe) and pair instability supernovae (PISNe) are the result of a thermonuclear runaway in the presence of a background electron-positron pair plasma. As such, their evolution and resultant black hole (BH) masses could possibly be affected by screening corrections due to the electron pair plasma. Aims. Sensitivity of PISNe and PPISNe to relativistic weak screening has been explored. Methods. In this paper a weak screening model that includes effects from relativistic pair production has been developed and applied at temperatures approaching and exceeding the thresh old for pair production. This screening model replaces "classical" screening commonly used in astrophysics. Modifications to the weak screening electron Debye length are incorporated in a computationally tractable analytic form with. Results. In PPISNe the BH masses were found to increase somewhat at high temperatures, though this increase is small. The BH collapse is also found to occur at earlier times, and the pulsational morphology also changes. In addition to the resultant BH mass, the sensitivity to the screening model of the pulsational period, the pulse structure, the PPISN-to-PISN transition, and the shift in the BH mass gap has been analyzed. The dependence of the composition of the ejected mass was also examined.

astro-ph.SR↗

arXiv2021

Dynamical Screening Effects on Big Bang Nucleosynthesis

A moving ion in plasma creates a deformed electric potential depending on the ion velocity, which leads to the distinct screening effect compared to the standard static Salpeter formula. In this paper, adopting the test charge method, we explore the dynamical screening effects on big bang nucleosynthesis (BBN). We find that the high temperature in the early universe causes the ion velocity to be faster than the solar condition so that the electric potential is effectively polarized. However, the low density of background plasma components significantly suppresses the dynamical screening effects on thermonuclear reaction rates during the BBN epoch. We compare our results with several thermonuclear reaction rates for solar fusion considering the dynamical screening effects. Also, we discuss the additional plasma properties in other astrophysical sites for the possible expansion from the present calculation in the future.

nucl-th↗

arXiv2021

Impact of hypernova νp-process nucleosynthesis on the galactic chemical evolution of Mo and Ru

We calculate Galactic Chemical Evolution (GCE) of Mo and Ru by taking into account the contribution from $νp$-process nucleosynthesis. We estimate yields of $p$-nuclei such as $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ through the $νp$-process in various supernova (SN) progenitors based upon recent models. In particular, the $νp$-process in energetic hypernovae produces a large amount of $p$-nuclei compared to the yield in ordinary core-collapse SNe. Because of this the abundances of $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ in the Galaxy are significantly enhanced at [Fe/H]=0 by the $νp$-process. We find that the $νp$-process in hypernovae is the main contributor to the elemental abundance of $^{92}$Mo at low metallicity [Fe/H$]<-2$. Our theoretical prediction of the elemental abundances in metal-poor stars becomes more consistent with observational data when the $νp$-process in hypernovae is taken into account.

astro-ph.GA↗

arXiv2021

Thermonuclear 17O(n,gamma)18O reaction rate and its astrophysical implications

A new thermonuclear $^{17}$O($n$,$γ$)$^{18}$O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have firstly calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte-Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 $\sim$ 2 GK, by up to a factor of $\sim$80. The astrophysical impacts of our rate have been examined in both $s$-process and $r$-process models. In our main $s$-process model which simulates flash-driven convective mixing in metal deficient asymptotic giant branch stars, both $^{18}$O and $^{19}$F abundances in interpulse phases are enhanced dramatically by factors of $\sim 20$--$40$ due to the new larger $^{17}$O($n$,$γ$)$^{18}$O rate. It shows, however, that this reaction hardly affects the weak $s$-process in massive stars since the $^{17}$O abundance never becomes significantly large in the massive stars. For the $r$-process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting "loophole" effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model, however, these significant differences are almost completely washed out if the fission recycling is considered.

nucl-th↗

arXiv2021

Measurements of $^{160}$Dy($p,γ$) at energies relevant for astrophysical $γ$ process

Rare information on photodisintegration reactions of nuclei with mass numbers $A \approx 160$ at astrophysical conditions impedes our understanding of the origin of $p$-nuclei. Experimental determination of the key ($p,γ$) cross sections has been playing an important role to verify nuclear reaction models and to provide rates of relevant ($γ,p$) reactions in $γ$-process. In this paper we report the first cross section measurements of $^{160}$Dy($p,γ$)$^{161}$Ho and $^{161}$Dy($p,n$)$^{161}$Ho in the beam energy range of 3.4 - 7.0 MeV, partially covering the Gamow window. Such determinations are possible by using two targets with various isotopic fractions. The cross section data can put a strong constraint on the nuclear level densities and gamma strength functions for $A \approx$ 160 in the Hauser-Feshbach statistical model. Furthermore, we find the best parameters for TALYS that reproduce the A $\thicksim$ 160 data available, $^{160}$Dy($p,γ$)$^{161}$Ho and $^{162}$Er($p,γ$)$^{163}$Tm, and recommend the constrained $^{161}$Ho($γ,p$)$^{160}$Dy reaction rates over a wide temperature range for $γ$-process network calculations. Although the determined $^{161}$Ho($γ$, p) stellar reaction rates at the temperature of 1 to 2 GK can differ by up to one order of magnitude from the NON-SMOKER predictions, it has a minor effect on the yields of $^{160}$Dy and accordingly the $p$-nuclei, $^{156,158}$Dy. A sensitivity study confirms that the cross section of $^{160}$Dy($p$, $γ$)$^{161}$Ho is measured precisely enough to predict yields of $p$-nuclei in the $γ$-process.

nucl-ex↗

arXiv2021

Progress in Nuclear Astrophysics of East and Southeast Asia

Nuclear astrophysics is an interdisciplinary research field of nuclear physics and astrophysics, seeking for the answer to a question, how to understand the evolution of the Universe with the nuclear processes which we learn. We review the research activities of nuclear astrophysics in east and southeast Asia which includes astronomy, experimental and theoretical nuclear physics and astrophysics. Several hot topics such as the Li problems, critical nuclear reactions and properties in stars, properties of dense matter, r-process nucleosynthesis and $ν$-process nucleosynthesis are chosen and discussed in further details. Some future Asian facilities, together with physics perspectives, are introduced.

nucl-ex↗

arXiv2021

Chiral Selection, Isotopic Abundance Shifts, and Autocatalysis of Meteoritic Amino Acids

The discovery of amino acids in meteorites has presented two clues to the origin of their processing subsequent to their formation: a slight preference for left-handedness in some of them, and isotopic anomalies in some of their constituent atoms. In this article we present theoretical results from the Supernova Neutrino Amino Acid Processing (SNAAP) model, which uses electron anti-neutrinos and the magnetic fields from source objects such as supernovae or colliding neutron stars to selectively destroy one amino acid chirality and to create isotopic abundance shifts. For plausible magnetic fields and electron anti-neutrino fluxes, non-zero, positive enantiomeric excesses, $ee$s, defined to be the relative left/right asymmetry in an amino acid population, are reviewed for two amino acids, and conditions are suggested that would produce $ee>0$ for all of the $α$-amino acids. The relatively high energy anti-neutrinos that produce the $ee$s would inevitably also produce isotopic anomalies. A nuclear reaction network was developed to describe the reactions resulting from them and the nuclides in the meteorites. At similar anti-neutrino fluxes, assumed recombination of the detritus from the anti-neutrino interactions is shown to produce appreciable isotopic anomalies in qualitative agreement with those observed for D/$^1$H and $^{15}$N/$^{14}$N. The isotopic anomalies for $^{13}$C/$^{12}$C are predicted to be small, as are also observed. Autocatalysis may be necessary for any model to produce the largest $ee$s observed in meteorites. This allows the constraints of the original SNAAP model to be relaxed, increasing the probability of meteoroid survival in sites where amino acid processing is possible. These results have obvious implications for the origin of life on Earth.

astro-ph.EP↗

arXiv2021

Impacts of Hawking Radiation from Primordial Black Holes in Critical Collapse Model on the Light Element Abundances

We study the photodisintegration process triggered by the nonthermal electromagnetic Hawking radiation from primordial black holes (PBHs) in critical collapse model. We consider the simplest case that all PBHs formed at a single epoch stemming from an inflationary spectrum with a narrow peak, and an extended mass distribution is obtained due to critical phenomena of gravitational collapse. The presence of a low-mass tail of critical collapse mass function could lead to an enhancement of energetic photon emissions from Hawking radiation of PBHs. Nuclear photodisintegration rates are calculated with a nonthermal photon spectrum derived by solving the Boltzmann equation iteratively. The exact spectrum is much different than that based on an often-used analytical bended power-law spectrum and it is found to significantly depend on the adopted PBH mass functions. With the newest observational limit on the $^3$He abundance in Galactic H II regions, the updated $^3$He constraints on PBH mass spectrum in the horizon mass range $10^{12} - 10^{13}$ g are derived. Our results for the first time show that $^3$He constraints on the critical mass function are about one order of magnitude severer than the monochromatic one although the fraction of PBHs in the low-mass tail region is relatively small. The $^6$Li elemental abundance is also enhanced significantly for the critical mass function. More precise measurement of $^6$Li abundance is highly desirable to provide a promising constraint on PBHs in the future. For monochromatic mass function, we provide the analytical bounds for photodisintegration and hadrodissociation from PBH radiation, and we report discrepancies between our updated $^3$He constraints and the previous results.

astro-ph.CO↗

arXiv2021

Enhancement of Lithium in Red Clump Stars by the Additional Energy Loss Induced by New Physics

Since 7Li is easily destroyed in low temperatures, the surface lithium abundance decreases as stars evolve. This is supported by the lithium depletion observed in the atmosphere of most red giants. However, recent studies show that almost all of red clump stars have high lithium abundances A(Li)>-0.9, which are not predicted by the standard theory of the low-mass stellar evolution. In order to reconcile the discrepancy between the observations and the model, we consider additional energy loss channels which may come from physics beyond the Standard Model. A(Li) slightly increases near the tip of the red giant branch even in the standard model with thermohaline mixing because of the 7Be production by the Cameron-Fowler mechanism, but the resultant 7Li abundance is much lower than the observed values. We find that the production of 7Be becomes more active if there are additional energy loss channels, because themohaline mixing becomes more efficient and a heavier helium core is formed.

astro-ph.SR↗

arXiv2021

Contribution of collapsars, supernovae, and neutron star mergers to the evolution of r-process elements in the Galaxy

We study the evolution of rapid neutron-capture process (r-process) isotopes in the Galaxy. We analyze relative contributions from core collapse supernovae (CCSNe), neutron star mergers (NSMs) and collapsars under a range of astrophysical conditions and nuclear input data. Although the r-process in each of these sites can lead to similar (or differing) isotopic abundances, our simulations reveal that the early contribution of r-process material to the Galaxy was dominated by CCSNe and collapsar r-process nucleosynthesis, while the NSM contribution is unavoidably delayed even under the assumption of the shortest possible minimum merger time.

astro-ph.GA↗