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Journal Articles

A Relativistic quantum approach to neutrino and antineutrino emission via the direct Urca process in strongly magnetized neutron-star matter

Maruyama, Tomoyuki*; Baha Balantekin, A.*; Cheoun, M.-K.*; Kajino, Toshitaka*; Kusakabe, Motohiko*; Mathews, G. J.*

Physics Letters B, 824, p.136813_1 - 136813_8, 2022/01

Journal Articles

Further signatures to support the tetraquark mixing framework for the two light-meson nonets

Kim, H.*; Kim, K. S.*; Cheoun, M.-K.*; Jido, Daisuke*; Oka, Makoto

Physical Review D, 99(1), p.014005_1 - 014005_15, 2019/01

 Times Cited Count:7 Percentile:41.49(Astronomy & Astrophysics)

We investigate additional signatures to support the tetraquark mixing framework that has been recently proposed as a possible structure for the two nonets. We reexamine the mass ordering generated from the tetraquark nonets and show that this mass ordering is satisfied by the two nonets although the ordering in the heavy nonet is marginal. The marginal mass ordering can be regarded as another signature for tetraquarks because it can be explained partially by the hyperfine masses calculated from the tetraquark mixing framework. As a peculiar signature distinguished from the other approaches, we investigate the fall-apart coupling strengths into two vector mesons from our tetraquarks. Coupling strengths into the two-vector modes are found to enhance strongly in the heavy nonet while they are suppressed in the light nonet. The coupling ratios are found to be huge. This trend in the two-vector modes can provide another testing ground for the tetraquark mixing framework. Some experimental evidence related to the phenomena is discussed particularly from the resonances belonging to the heavy nonet.

Journal Articles

Tetraquark mixing framework for isoscalar resonances in light mesons

Kim, H.*; Kim, K. S.*; Cheoun, M.-K.*; Oka, Makoto

Physical Review D, 97(9), p.094005_1 - 094005_17, 2018/05

 Times Cited Count:14 Percentile:59.45(Astronomy & Astrophysics)

A tetraquark mixing framework has been applied successfully to the isoscalar resonances, $$f_0(500)$$, $$f_0(980)$$, $$f_0(1370)$$ and $$f_0(1500)$$. Tetraquarks in this framework can have two spin configurations containing either spin-0 diquark or spin-1 diquark and each configuration forms a nonet in flavor space. The two spin configurations are found to mix strongly through the color-spin interactions. Their mixtures, which diagonalize the hyperfine masses, can generate the physical resonances constituting two nonets, which, in fact, coincide roughly with the experimental observation. We identify that $$f_0(500)$$, $$f_0(980)$$ are the isoscalar members in the light nonet, and $$f_0(1370)$$, $$f_0(1500)$$ are the similar members in the heavy nonet. The complication arises because the isoscalar members of each nonet are subject to an additional flavor mixing known as Okubo-Zweig-Iizuka rule. The tetraquark mixing framework including the flavor mixing is tested for the isoscalar resonances in terms of the mass splitting and the fall-apart decay modes. The mass splitting among the isoscalar resonances is found to be consistent qualitatively with their hyperfine mass splitting strongly driven by the spin configuration mixing, which suggests that the tetraquark mixing framework works. The fall-apart modes from our tetraquarks also seem to be consistent with the experimental modes. We also discuss possible existence of the spin-1 tetraquarks that can be constructed by the spin-1 diquark.

Journal Articles

Testing the tetraquark structure for the X resonances in the low-lying region

Kim, H.*; Kim, K. S.*; Cheoun, M.-K.*; Jido, Daisuke*; Oka, Makoto

European Physical Journal A, 52(7), p.184_1 - 184_8, 2016/07

 Times Cited Count:13 Percentile:68.51(Physics, Nuclear)

Assuming four-quark structure for the $$X$$ resonances in low-lying region, we calculate their masses using the color-spin interaction. In specific, the hyperfine masses of the color-spin interaction are calculated for the possible states in spin-0, spin-1, spin-2 channels. The two states in spin-0 channel as well as the two states in spin-1 channel are diagonalized in order to generate the physical hyperfine masses. By matching the difference in hyperfine masses with the splitting in corresponding hadron masses and using the $$X(3872)$$ mass as an input, we estimate the masses corresponding to the states $$J^{PC}=0^{++},1^{+-},2^{++}$$. We find the masses of two states in $$1^{+-}$$ are close to those of $$X(3823)$$, $$X(3900)$$, and the mass of the $$2^{++}$$ state is close to that of $$X(3940)$$. For them, the discrepancies are about $$sim 10$$ MeV. This may suggest that the quantum numbers of the controversial states are $$X(3823)=1^{+-}, X(3900)=1^{+-}, X(3940)=2^{++}$$. In this work, we use the same inputs parameters, the constituent quark masses and the strength of the color-spin interaction, that have been adopted in the previous work on the $$D$$ or $$B$$-meson excited states. There, it was shown that the four-quark structure can be manifested in their excited states. Thus, our results in this work provide a consistent treatment on open- and hidden-charm mesons as far as the four-quark model is concerned.

Journal Articles

Supernova neutrino nucleosynthesis of the radioactive $$^{92}$$Nb observed in primitive meteorites

Hayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Iwamoto, Nobuyuki; Cheoun, M. K.*; Mathews, G. J.*

Astrophysical Journal Letters, 779(1), p.L9_1 - L9_5, 2013/12

 Times Cited Count:28 Percentile:63.21(Astronomy & Astrophysics)

Short-lived radioactivities are used as nuclearcosmochronometers for understanding the free decay time from the last nucleosynthesis episode until the time of solar system formation (SSF). $$^{92}$$Nb (half-life of 34.7 Myr) is one of a short-lived isotope existed at SSF. However, there is a controversy in that the inferred initial abundance ratios for $$^{92}$$Nb/$$^{93}$$Nb at the time of SSF cluster around two different values; one is near 10$$^{-3}$$, while the other is near 10$$^{-5}$$. Moreover, the astrophysical mechanism for the synthesis of $$^{92}$$Nb has remained an unsolved problem. Here we argue that conventional nucleosynthesis mechanisms cannot produce $$^{92}$$Nb and propose a new mechanism for the nucleosynthesis of this isotopebased upon neutrino induced reactions occurring during core-collapse supernova explosions.

Journal Articles

Neutrino reactions on $$^{138}$$La and $$^{180}$$Ta via charged and neutral currents by the quasiparticle random-phase approximation

Cheoun, M. K.*; Ha, E.*; Hayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi

Physical Review C, 82(3), p.035504_1 - 035504_7, 2010/09

 Times Cited Count:38 Percentile:88.02(Physics, Nuclear)

We investigate neutrino-induced reactions on heavy nuclei. Charged current (CC) reactions,$$^{138}$$Ba($$nu_e$$, $$e$$$$^-$$)$$^{138}$$La and $$^{180}$$Hf($$nu_e$$, $$e$$$$^-$$)$$^{180}$$Ta are calculated by a quasi-particle random phase approximation (QRPA) with pairing correlations. For neutral current (NC) reactions, $$^{139}$$La($$nu,nu'$$)$$^{139}$$La$$^*$$ and $$^{181}$$Ta($$nu,nu'$$)$$^{181}$$Ta$$^*$$, we generate ground and excited states of odd-even target nuclei, $$^{139}$$La and $$^{181}$$Ta, by operating one quasi-particle to even-even nuclei. Numerical results for CC reactions are shown to be consistent with recent semi-empirical data deduced from the Gamow-Teller strength distributions measured in the ($$^3$$He,$$t$$) reaction. Results for NC reactions are estimated to be smaller by a factor about 4 to 5 rather than those by CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core collapsing supernova are presented for further applications to the network calculations for relevant nuclear abundances.

Oral presentation

Supernova neutrino nucleosynthesis of a radioactivity $$^{92}$$Nb

Hayakawa, Takehito; Kajino, Toshitaka*; Nakamura, Ko*; Chiba, Satoshi; Iwamoto, Nobuyuki; Cheoun, M. K.*; Mathews, G. J.*

no journal, , 

Relatively short-lived radioactivities are used as nuclear cosmochronometers for determining the free decay time from the last nucleosynthesis episode strongly affecting to the material of the solar system to the solar system formation. An unstable isotope of $$^{92}$$Zr with a half-life of 34.7 Myr is extinct in the present solar system, which can be used as a new cosmochronometer. We discuss the contribution of the neutrino-process.

Oral presentation

Synthesis of odd-odd nuclei by supernova neutrino process

Hayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Cheoun, M. K.*; Mathews, G. J.*; Iwamoto, Nobuyuki

no journal, , 

Huge amount of neutrinos are generated from proto neutron stars in early phase of supernova explosions. They produce new isotopes from pre-existing isotopes by neutrino-nucleus interactions in outer layers of supernovae. In general, odd-odd isotopes have rare isotopic abundance compared with other isotopes and thus synthesis by neutrino can contribute its abundance. Such odd-odd isotopes are observed in the solar abundances and meteorites. We discuss nucleosynthesis by neutrino-induced reactions with a supernova model.

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