arXiv subjects

Toshitaka Kajino

Publications and source records attributed to Toshitaka Kajino.

At least 19 recordsLinked to original sources

arXiv2026

Constraints of Big Bang Nucleosynthesis and Cosmological Observations on varying Higgs VEV

The Higgs vacuum expectation value (VEV) alters both the electroweak and strong interaction rates. We study both effects on Big Bang Nucleosynthesis (BBN) and seek concordance between observed primordial abundances of light elements and cosmological constraints from cosmic microwave background (CMB) fluctuations and anisotropies. We find a strong negative correlation between primordial 4He abundance and the Higgs VEV. Consequently, using a 1.58% uplift of the Higgs VEV during BBN from the current value, an agreement can be achieved among the new primordial 4He abundance, observed by the EMPRESS group, Deuterium abundance determined from absorption lines in the Lyman-alpha forest along the line-of-sight of high-redshift quasars, and the lithium abundance on the Spite plateau. This agreement requires a baryon-to-photon ratio different from the CMB determination, indicating the need for non-standard cosmological evolution between BBN and recombination epochs.We also demonstrate that a 0.2% uplift in the Higgs VEV can partially alleviate the "cosmic Li problem", keeping consistency with the CMB with remaining discrepancy potentially accounted for by stellar depletion mechanisms.

astro-ph.CO↗

arXiv2026

Strong magnetic field inside degenerate relativistic plasma and the impacts on the neutrino transport in Core-Collapse Supernovae

We investigate the impacts of strong magnetic fields on neutrino transport in core-collapse supernovae (CCSNe) using the leakage scheme. Magnetic field quantizes the momentum of electrons and positrons, resulting in the modification of weak-interaction cross sections and the chemical potentials of electrons and positrons. We derive formula for neutrino leakage scheme including these two impacts and perform 1D CCSN simulations with \texttt{GR1D}. Magnetic field strengths from $10^{16}$\,G to $10^{17}$\,G were applied to postbounce phase. The results show that the neutrino opacities are enhanced due to the amplified interaction rates, with stronger effects on anti-neutrinos. This leads to larger neutrinosphere radii, longer neutrino trapping timescales, reduced peak luminosities, and delayed peak energies.

astro-ph.HE↗

arXiv2026

Electron-capture rates in the medium-mass nuclei $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge within deformed quasiparticle random-phase approximation

Electron-capture (EC) rates in medium-mass nuclei are governed by Gamow--Teller (GT) strength distributions and provide important input for stellar weak-interaction processes. In this work, we investigate the deformation dependence of the GT strengths and stellar EC rates in selected medium-mass nuclei in and near the $pf$ shell, namely $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge. The GT$^{(+/-)}$ strength distributions are calculated in the deformed quasiparticle random-phase approximation (DQRPA) on a single-particle basis obtained by the Skyrme SGII interaction, while the stellar EC rates are evaluated from the resulting $B(\mathrm{GT}^+)$ strengths using the standard phase-space formalism. The potential-energy curves are used to identify shape softness and possible shape coexistence in the nuclei under consideration. We find that deformation strongly modifies the GT strength distributions by changing the centroid energies, resonance splitting, and fragmentation patterns. In particular, a pronounced shape dependence of the GT$^{(+/-)}$ strengths is found for $^{56}$Ni and $^{64}$Ge, whereas $^{60}$Zn is characterized by a favoured prolate minimum and $^{48}$Ti exhibits a soft near-spherical/prolate landscape. By contrast, the corresponding EC rates are generally much less sensitive to deformation than the differential GT response itself, except at low temperatures and low densities where the low-lying GT$^+$ strength becomes decisive because of the negative EC $Q$-value in the electron phase space. Available charge-exchange data for $^{48}$Ti and $^{56}$Ni are used as benchmarks of the model predictions. The present results provide microscopic constraints on the role of deformation and shape coexistence in stellar weak rates for selected medium-mass nuclei, including proton-rich isotopes near the $N = Z$ line.

nucl-th↗

arXiv2026

The Sc, Ti, and V Abundance Discrepancy: Testing High-Mass IMF Variation and Massive-Star Rotation

Scandium, titanium, and vanadium can be synthesized primarily in massive stars. Yet many of the current Galactic chemical evolution models under-produce these elements at early epochs. Motivated by evidence that the initial mass function varied in the past on the Galactic disc, we examine how assumptions about massive-star rotation and the initial mass function affect the inferred evolution of Sc, Ti, and V. We compute a grid of one-zone Galactic chemical evolution models that varies the initial rotational velocity of massive stars and the high-mass slope of the initial mass function. We compare the resulting [X/Fe] vs [Fe/H] for X= Sc, Ti, and V tracks and cross-element correlations with Galactic abundance data. We find that adopting rotating massive-star yields with an initial rotational velocity of 300 km/s brings the model trends closer to metal-poor observations, especially for halo stars ([Fe/H] $< -2$), and improves the joint behavior of Sc, Ti, and V. Variations of the high-mass slope of the initial mass function produce a secondary modulation. The remaining tensions, most apparent at solar to super-solar metallicities, motivate future work with a more complete treatment of the enrichment physics and model uncertainties.

astro-ph.GA↗

arXiv2026

High-Precision Measurement of D($γ$, $n$)$p$ Photodisintegration Reaction and Implications for Big-Bang Nucleosynthesis

We report on a high-precision measurement of the D($γ$,\,$n$)$p$ photodisintegration reaction at the newly commissioned Shanghai Laser Electron Gamma Source (SLEGS), employing a quasi-monochromatic $γ$-ray beam from Laser Compton Scattering. The cross sections were determined over $E_γ$=2.327--7.089 MeV, achieving up to a factor of 2.2 improvement in precision near the neutron separation threshold. Combined with previous data in a global Markov chain Monte Carlo (MCMC) analysis using dibaryon effective field theory, we obtained the unprecedentedly precise $p$($n$,\,$γ$)D cross sections and thermonuclear rate, with a precision up to $\approx$4 times higher than previous evaluations. Implemented in a standard Big-Bang Nucleosynthesis (BBN) framework, this new rate decreases uncertainty of the key cosmological parameter of baryon density $Ω_b h^2$ by up to $\approx$16\% relative to the LUNA result. A residual $\approx$1.2$σ$ tension between $Ω_b h^2$ constrained from primordial D/H observations and CMB measurements persists, highlighting the need for improved $dd$ reaction rates and offering potential hints of new physics beyond the standard model of cosmology.

nucl-ex↗

arXiv2025

Impact of experimental mass of $^{70}$Kr on the $^{68}$Se waiting-point in $rp$-process

The recent mass measurement of $^{70}$Kr using the $Bρ$-defined isochronous mass spectrometry yields a mass excess of $-41320(140)$ keV, indicating a 220-keV increase in binding energy compared to the AME2020 prediction. We utilize this experimental mass -- the last piece of information needed -- to model the potential waiting point $^{68}$Se in $rp$-process and quantitatively constrain the sequential $p$-capture reaction flow bypassing this waiting point. Our investigation shows that the more tightly bound nature of $^{70}$Kr enhances this reaction flow up to a factor of four. This enhancement reduces the effective half-life of $^{68}$Se. {A} one-zone X-ray burst model calculations reveal that the higher flow of $^{70}$Kr has distinct effects on the tail structure of light curve and the final SnSbTe abundances in the ashes due to a stronger $rp$-process heating.

nucl-th↗

arXiv2025

High Energy Particle Production from Proton Synchrotron Radiation in Strong Magnetic Fields in Relativistic Quantum Field Theory

We investigate photon, pion, and rho-meson production from proton synchrotron radiation in the presence of strong magnetic fields. The proton decay widths and the luminosities of the emitted particles are calculated within a relativistic quantum framework that incorporates Landau quantization. A scaling rule is derived for the transition probability between different Landau levels. This allows an evaluation of transitions for extremely high Landau numbers exceeding $10^{15}$. Furthermore, we calculate the momentum distribution of the emitted particles by properly including the proton recoil effect associated with particle emission. The results differ significantly from conventional semiclassical approaches.

hep-ph↗

arXiv2025

A Systematic Study of Magnetic Fields Impacts on Neutrino Transport in Core-Collapse Supernovae

We quantify the impact of strong magnetic fields (assuming $B=B_0\cdot r_0^3/r^3$ with $B_0\gtrsim 10^{16}$ G) on the neutrino transport in core-collapse supernovae (CCSNe). Magnetic fields quantize the momenta of electrons and positrons, resulting in an enhanced absorption cross section for low-energy neutrinos and suppressed chemical potentials for $e^\pm$. We include these changes in the M1 scheme for neutrino transport and perform 1-D CCSNe simulations with \texttt{GR1D}. The increased low-energy cross sections reduce the $\barν_e$ mean energy $\langle E_{\barν_e}\rangle$ while elevating the neutrino number luminosities $\mathcal{L_ν}$ for both $ν_e$ and $\barν_e$ due to the lower energy weighted spectra. The reduction of chemical potential enhances the $\barν_e$ emission while suppressing that of $ν_e$, thereby driving an increase in the electron fraction behind the stalled shock at $\sim30$--$100$ km. This further amplifies $\langle E_{ν_e}\rangle$ through an increased electron density. Consequently, magnetic fields amplify $L_{ν_e}$ by increasing both $\mathcal{L}_{ν_e}$ and $\langle E_{ν_e}\rangle$ whereas for $\barν_e$, the rise in $\mathcal{L}_{\barν_e}$ is offset by a decreased $\langle E_{\barν_e}\rangle$, leading to a minimal change in $L_{\barν_e}$. A systematic parameter scan of dipole field configurations suggests that, for $r_0 > 30$ km, $\langle E_{\barν_e} \rangle$ is significantly suppressed and $L_{ν_e}$ is enhanced if $B_0 \geq {2.7} \times 10^{16}$ G. These magnetic effects become negligible for $B_0$ below $\sim {7.4} \times 10^{15}$ G.

astro-ph.HE↗

arXiv2025

Dense Matter in Neutron Stars with eXTP

In this White Paper, we present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission to constrain the equation of state of dense matter in neutron stars, exploring regimes not directly accessible to terrestrial experiments. By observing a diverse population of neutron stars - including isolated objects, X-ray bursters, and accreting systems - eXTP's unique combination of timing, spectroscopy, and polarimetry enables high-precision measurements of compactness, spin, surface temperature, polarimetric signals, and timing irregularity. These multifaceted observations, combined with advances in theoretical modeling, pave the way toward a comprehensive description of the properties and phases of dense matter from the crust to the core of neutron stars. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is planned to be launched in early 2030.

astro-ph.HE↗

arXiv2025

New Determination of the $^{14}$C(n, $γ$)$^{15}$C Reaction Rate and Its Astrophysical Implications

We present a novel experiment to investigate the spectroscopic factor of the $^{15}$C ground state for the first time using single-neutron $removal$ transfer reactions on $^{15}$C. Two consistent spectroscopic factors were derived from the (p, d) and (d, t) reactions, which were subsequently used to deduce the $^{14}$C(n, $γ$)$^{15}$C reaction cross section and the corresponding stellar reaction rate. A typical cross section of (3.89 $\pm$ 0.76) $μ$b is determined at $E_\mathrm{_{c.m.}}$ = 23.3 keV. At the temperature range of 0.01-4 GK, our new reaction rate is 2.4-3.7 times higher than that of the first direct measurement and 20\%-25\% lower than that of the most recent direct measurement, respectively. Moreover, it is interesting that we can associate a long-standing nuclear structure issue, i.e., the so-called ``quenching'' effect, with this astrophysically relevant reaction. Finally, motivated by astrophysical interests of this reaction decades ago, implications of our new rate on several astrophysical problems are evaluated using state-of-the-art theoretical models. Our calculations demonstrate that the abundances of $^{14}$N and $^{15}$N can be enhanced in the inner regions of asymptotic giant branch (AGB) stars, though with minimal impact on the chemical compositions of the interstellar medium. In the inhomogeneous Big Bang nucleosynthesis, the updated reaction rate can lead to a $\sim 20\%$ variation in the final yields of $^{15}$N in neutron rich regions. For the $r$-process in the core-collapse supernovae, a slight difference of $\sim 0.2\%$ in the final abundances of heavy elements with $A > 90$ can be found by using our new rate.

nucl-ex↗

arXiv2025

KDAR neutrino scattering for $^{12}$C target via charged current and muon angular distribution

We calculate muon-neutrino ($ν_μ$) scattering off $^{12}$C via charged current (CC) by exploiting the 236 MeV ${ν_μ}$ from the kaon-decay-at-rest (KDAR). In this energy region, since both inelastic scattering below the quasielastic (QE) region and the QE scattering contribute simultaneously, we combine the inelastic scattering obtained by the QRPA and the QE scattering obtained by distorted wave born approximation (DWBA) based on the relativistic mean field (RMF) theory. We compare the results to the data from MiniBooNE. Further, since the KDR $ν_μ$ CC scattering may have angle dependence of outgoing muon, we investigate the differential angular dependent cross section in the ${ν_μ}$-$^{12}$C scattering and compare to the results by $ν_e$-$^{12}$C scattering. These results could be useful for the calibration of the forthcoming KDAR neutrino cross section experiments.

nucl-th↗

arXiv2025

Stellar $β^{-}$-decay rate of $^{63}$Ni and its impact on the ${s}$-process nucleosynthesis in massive stars

The $β^{-}$-decay rate of $^{63}$Ni, an important branching point, affects the subsequent nucleosynthesis in the weak component of the slow-neutron capture process (weak $s$-process). To evaluate the impact of the uncertainties of stellar lifetime of $^{63}$Ni on abundances, we calculate the contribution to $β^{-}$-decay rates from its excited states using the large-scale shell model with various interactions and also explore the atomic effects in the highly ionized plasma. In the core He burning stage and the shell C burning stage of massive stars, our new rates can be larger than those from Takahashi and Yokoi(1987) by up to a factor of 4 and 6, respectively. We evaluate the impact of the stellar decay rates of $^{63}$Ni on the nucleosynthesis of $A=60\sim90$ in a star with an initial mass of 25 $M_{\bigodot}$ and solar metalicity. We find that the new rates can lead to the abundance changes of $^{64}$Ni, $^{63}$Cu, $^{65}$Cu, $^{64}$Zn, $^{66}$Zn, $^{67}$Zn, and $^{68}$Zn by up to $18\%$, $14\%$, $7\%$, $98\%$, $16\%$, $15\%$, and $13\%$, respectively, after the shell C burning stage at the Lagrangian mass coordinate $M_{r}=2M_{\bigodot}$. The enhancement of the decay rate of $^{63}$Ni increases the weak $s$-process efficiency of nuclei after $^{65}$Cu.

astro-ph.HE↗

arXiv2025

Big Bang Nucleosynthesis constraints on the Energy-Momentum Squared Gravity: The $\mathbb{T}^{2}$ model

Scale-independent energy-momentum squared gravity (EMSG) allows different gravitational couplings for different types of sources and has been proven to have interesting implications in cosmology. In this paper, the Big Bang Nucleosynthesis (BBN) formalism and the latest observational constraints on nuclear abundances are being used to put bounds on this class of modified gravity models. Using the tight constraint from BBN on the correction term in the Friedmann equation in EMSG scenario, we report the allowed deviation from the standard cosmic expansion rate.

astro-ph.CO↗

arXiv2025

Exploring the Neutrino Mass Hierarchy from Isotopic Ratios of Supernova Nucleosynthesis Products in Presolar Grains

We study the nucleosynthesis in a core-collapse supernova model including newly calculated neutrino-induced reaction rates with both collective and Mikheyev-Smirnov-Wolfenstein (MSW) neutrino-flavor oscillations considered. We show that the measurement of a pair of $^{11}$B/$^{10}$B and $^{138}$La/$^{139}$La or $^6$Li/$^7$Li and $^{138}$La/$^{139}$La in presolar grains that are inferred to have originated from core-collapse supernovae could constrain the neutrino mass hierarchy. The new shell-model and the model of quasi-particle random phase approximation in the estimate of three important neutrino-induced reactions, $ν+^{16}$O, $ν+^{20}$Ne, and $ν+^{138}$Ba are applied in our reaction network. The new rates decrease the calculated $^{7}$Li/$^{6}$Li ratio by a factor of five compared with the previous study. More interestingly, these new rates result in a clear separation of the isotopic ratio of $^{11}$B/$^{10}$B between normal and inverted mass hierarchies in the O/Ne, O/C, and C/He layers where $^{138}$La abundance depends strongly on the mass hierarchy. In these layers, the sensitivity of the calculated abundances of $^{10,11}$B and $^{6,7}$Li to the nuclear reaction uncertainties is also tiny. Therefore, we propose that the $^{11}$B/$^{10}$B vs. $^{138}$La/$^{139}$La and $^6$Li/$^7$Li vs. $^{138}$La/$^{139}$La in type X silicon carbide grains sampled material from C/He layer can be used as a new probe to constrain the neutrino mass hierarchy.

astro-ph.SR↗

arXiv2024

Photon vortex generation from nonlinear Compton scattering in Feynman approach

In the present study, we show calculation of nonlinear Compton scattering with circularly polarized photons in a cylindrical coordinate using Feynman diagram to calculate photon vortex generation in intermediate states considering conservation of angular momentum. We take two different vortex wave functions based on Bessel function for the emitted photon and the electron after emission of the photon, which are the eigenstate of z component of the total angular momentum (zTAM) when a particle propagates along z axis. The result shows that when an electron absorbs N photons a photon vortex with a zTAM = N is predominantly radiated, but there are still very small contributions of photons with a zTAM = (N-1) and (N +1) due to the spin flip of the initial electron. This means even when an electron absorbs only a single photon, the electron may emit a photon vortex of a zTAM of 2 h-bar. However, the numerical calculations show that the contribution of the spin flip is four orders of magnitude smaller than that of the dominant radiation. We also discuss the circular polarization for the generated photon vortices.

hep-ph↗

arXiv2024

Deep learning for nuclear masses in deformed relativistic Hartree-Bogoliubov theory in continuum

Most nuclei are deformed, and these deformations play an important role in various nuclear and astrophysical phenomena. Microscopic nuclear mass models have been developed based on covariant density functional theory to explore exotic nuclear properties. Among these, we adopt mass models based on the relativistic continuum Hartree-Bogoliubov theory (RCHB) with spherical symmetry and the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with axial symmetry to study the effects of deformation on the abundances produced during the rapid neutron-capture process (r-process). Since the DRHBc mass table has so far been completed only for even-Z nuclei, we first investigate whether a Deep Neural Network (DNN) can be used to extend the DRHBc mass table by focusing on nuclear binding energies. To incorporate information about odd-odd and odd-even isotopes into the DNN, we also use binding energies from AME2020 as a training set, in addition to those from the DRHBc mass table for even-Z nuclei. After generating an improved mass table through the DNN study, we conduct a sensitivity analysis of r-process abundances to deformation or mass variations using the RCHB$^\star$ and DRHBc$^\star$ mass tables (where $\star$ indicates that the mass table is obtained from the DNN study). For the r-process sensitivity study, we consider magnetohydrodynamic jets and collapsar jets. Our findings indicate that r-process abundances are sensitive to nuclear deformation, particularly within the mass range of $A=80-120$.

nucl-th↗

arXiv2024

Photo-nuclear reaction rates of $^{157,159}$Ho and $^{163,165}$Tm and their impact in the $γ$--process

Reliable photo-nuclear reaction rates at the stellar conditions are essential to understand the origin of the heavy stable neutron-deficient isotopes between $^{74}$Se and $^{196}$Hg-p-nuclei, however, many reaction rates of relevance still have to rely on the Hauser-Feshbach model due to rare experimental progress. One such case is in the mass range of 160 for Dy, Er, Ho and Tm isotopes. In this work we attempt to constrain the Hauser-Feshbach model in the TALYS package by reproducing the available experimental data of $^{160}$Dy($p,γ$)$^{161}$Ho and $^{162}$Er($p,γ$)$^{163}$Tm in the $A\sim 160$ mass region, and examine the effects of level density, gamma strength function and the optical model potential. The constrained model then allows us to calculate the reaction rates of $^{157, 159}$Ho($γ$, $p$) and $^{163,165}$Tm($γ$, $p$) for the $γ$-process nucleosynthesis in carbon-deflagration SNe Ia model. Our recommended rates differ from the JINA REACLIB by more than 1 order of magnitude in the temperature range of 2-3 GK. This results in the changes of final abundance of $p$-nuclei in the $A\sim 160$ mass range by -5.5-3\% from those with JINA, which means that the ($γ$, $p$) reactions uncertainty is not predominant for the synthesis of these nuclei.

astro-ph.SR↗

arXiv2024

Magnetic Effect on Potential Barrier for Nucleosynthesis II

We investigate the impact of magnetic fields on the potential barrier between two interacting nuclei. We addressed this by solving the Boltzmann equation and Maxwell's theory in the presence of a magnetic field, resulting in the determination of magnetized permittivity. Additionally, we derived the magnetized Debye potential, which combines the conventional Debye potential with an additional magnetic component. We then compared the Boltzmann approach with the Debye method. Both methods consistently demonstrate that magnetic fields increase permittivity. This enhanced permittivity leads to a reduction in the potential barrier, consequently increasing the reaction rate for nucleosynthesis. Furthermore, the dependence on temperature and electron density in each approach is consistent. Our findings suggest that magnetized plasmas, which have existed since the Big Bang, have played a crucial role in nucleosynthesis.

astro-ph.CO↗