arXiv subjects

Yasushi Kino

Publications and source records attributed to Yasushi Kino.

5 recordsLinked to original sources

arXiv2025

Radiative decay of muonic molecules in resonance states

In this study, we theoretically investigated x-ray spectra from the radiative decay of muonic deuterium molecules in resonance states dd$μ^\ast$, which plays an important role in a new kinetic model of muon catalyzed fusion ($μ$CF). The resonance states are Feshbach resonances located below the d$μ$($n=2$) + d threshold energy and radiatively decay into the continuum or bound states. The x-ray spectra having characteristic shapes according to the radial distribution of the two nuclei are obtained using precise three-body wave functions. We carefully examined the convergence of the x-ray spectra and achieved agreements between the length- and velocity-gauge calculations. We revealed a non-adiabatic kinetic energy distribution of the decay fragments, indicating that the radiative decay becomes a heating source of muonic atoms. We also investigated the decay branch that directly results in bound-state muonic molecules. Some resonance states dd$μ^\ast$ and dt$μ^\ast$ are found to have high branching ratios to the bound state where intramolecular nuclear fusion occurs. The formation of the muonic molecules in the bound states from metastable muonic atoms can be a fast track in the $μ$CF cycle which skips a slow path to form the bound state from the ground-state muonic atoms and increases the $μ$CF cycle rate. Although the spectra from the radiative decays are located in the energy range of $1.5$--$1.997$ keV, which is close to the K$α$ x-ray of 1.997 keV from muonic deuterium atoms, state-of-the-art microcalorimeters can distinguish them.

physics.atom-ph↗

arXiv2024

Complex scaling calculation of phase shifts for positron collisions with positive ions

We present phase-shift calculations for positron collisions with positive ions using a complex scaling method (CSM). Based on the findings of this study [R. Suzuki, T. Myo, and K. Katō, Prog. Theor. Phys. 113, 1273 (2005).], we propose a modification of the phase shift in the CSM calculation, in which phase shifts are derived only from the complex eigenenergies of the CSM Hamiltonian. This modification is based on the fact that the contributions of high-lying complex eigenenergies can be approximated as a constant value in the case of a small collision energy, where neither target excitation nor positronium formation occurs. The proposed modification limits the contribution of the complex eigenenergies to the vicinity of the collision energy, which is also intuitively acceptable. We present a geometrical formulation of the modification and demonstrative calculations of positron scattering off positive ions. Our results agree well with those reported in the literature for the targets Ne, Ar, Kr, Xe, H, He, He$^+$, and Li$^{2+}$. The phase shifts of positron scattering off a Li$^+$ ion have also been reported.

physics.atom-ph↗

arXiv2014

Revised Big Bang Nucleosynthesis with long-lived negatively charged massive particles: updated recombination rates, primordial 9Be nucleosynthesis, and impact of new 6Li limits

We extensively reanalyze effects of a long-lived negatively charged massive particle, X-, on big bang nucleosynthesis (BBN). The BBN model with an X- particle was originally motivated by the discrepancy between 6,7Li abundances predicted in standard BBN model and those inferred from observations of metal-poor stars. In this model 7Be is destroyed via the recombination with an X- particle followed by radiative proton capture. We calculate precise rates for the radiative recombinations of 7Be, 7Li, 9Be, and 4He with X-. In nonresonant rates we take into account respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in wave functions from those of point-charge nuclei. For a heavy X- mass, m_X \gtrsim 100 GeV, the d-wave --> 2P transition is most important for 7Li and 7,9Be, unlike recombination with electrons. Our new nonresonant rate of the 7Be recombination for m_X=1000 GeV is more than 6 times larger than the existing rate. Moreover, we suggest a new important reaction for 9Be production: the recombination of 7Li and X- followed by deuteron capture. We derive binding energies of X-nuclei along with reaction rates and Q-values. We then calculate BBN and find that the amount of 7Be destruction depends significantly on the charge distribution of 7Be. Finally, updated constraints on the initial abundance and the lifetime of the X- are derived in the context of revised upper limits to the primordial 6Li abundance. Parameter regions for the solution to the 7Li problem are revised, and the primordial 9Be abundances is revised.

astro-ph.CO↗

arXiv2013

7Be charge exchange between 7Be3+ ion and exotic long-lived negatively charged massive particle in big bang nucleosynthesis

The existence of an exotic long-lived negatively charged massive particle, i.e., X-, during big bang nucleosynthesis can affect primordial light element abundances. Especially, the final abundance of 7Li, mainly originating from the electron capture of 7Be, has been suggested to reduce by the 7Be destruction via the radiative X- capture of 7Be followed by the radiative proton capture of the bound state of 7Be and X- (7BeX). We suggest a new route of 7BeX formation, that is the 7Be charge exchange at the reaction of 7Be3+ ion and X-. The formation rate depends on the number fraction of 7Be3+ ion, the charge exchange cross section of 7Be3+, and the probability that produced excited states 7BeX* are converted to the ground state. We estimate respective quantities affecting the 7BeX formation rate, and find that this reaction pathway can be more important than ordinary radiative recombination of 7Be and X-. The effect of the charge exchange reaction is then shown in a latest nuclear reaction network calculation. Quantum physical model calculations for related reactions are needed to precisely estimate the efficiency of this pathway in future.

astro-ph.CO↗

arXiv2009

Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

nucl-th↗