arXiv subjects

K. Tsushima

Publications and source records attributed to K. Tsushima.

At least 37 records · Page 2Linked to original sources

arXiv2021

Effects of neutrino magnetic moment and charge radius constraints and medium modifications of the nucleon form factors on the neutrino mean free path in dense matter

Effects of neutrino charge radius and magnetic moment constraints obtained from the astrophysical observations and reactor experiments, as well as in-medium modifications of the weak and electromagnetic nucleon form factors of the matter on the neutrino electroweak interaction with dense matter, are estimated. We use a relativistic mean-field model for the in-medium effective nucleon mass and quark-meson coupling model for nucleon form factors. We analyze the neutrino scattering cross section and mean free path in cold nuclear matter. We find that the increase of the cross section relative to that without neutrino form factors results in the decrease of the neutrino mean free path when neutrino form factors and the in-medium modifications of the nucleon weak and electromagnetic form factors are simultaneously considered. The quenching of the neutrino mean free path is evaluated to be about 12-58\% for the values of $μ_ν= 3 \times 10^{-12} μ_B$ and $R_ν= 3.5 \times 10^{-5}~\textrm{MeV}^{-1}$ compared with that obtained for the $μ_ν=0$ and $R_ν=0$. The decrease of the neutrino mean free path is expected to decelerate the cooling of neutron stars. Each contribution of the neutrino form factors to the neutrino mean free path is discussed.

hep-ph↗

arXiv2021

[1]Title: $Υ$ and $η_b$ mass shifts in nuclear matter and the $^{12}$C nucleus bound states, [2]Title: $Υ$ and $η_b$ mass shifts in nuclear matter and the nucleus bound states

[1]Abstract: This is a contribution for the PANIC 2021 Proceedings based on the articles, Eur. Phys. J. A 57, 259 (2021) and the accompanied article $[$arXiv:2109.08636 $[$hep-ph$]]$ (Hadron 2021 contribution). We have estimated for the first time the mass shifts of the $Υ$ and $η_b$ mesons in symmetric nuclear matter by an SU(5) flavor symmetric effective Lagrangian approach, as well as the in-medium mass of $B^*$ meson by the quark-meson coupling (QMC) model. The attractive potentials for the $Υ$- and $η_b$-nuclear matter are obtained, and one can expect for these mesons to form nuclear bound states. We have indeed found such nuclear bound states with $^{12}$C nucleus, where the results for the $^{12}$C nucleus bound state energies are new, and we report here for the first time. [2]Abstract: We estimate for the first time the mass shifts (scalar potentials) in symmetric nuclear matter of the $Υ$ and $η_b$ mesons using an effective Lagrangian approach, as well as the in-medium mass of the $B^*$ meson by the quark-meson coupling model. The attractive potentials of both $Υ$ and $η_b$ are expected to be strong enough for these mesons to be bound to the $^4$He nucleus, and we have obtained such nuclear bound state energies.

hep-ph↗

arXiv2021

Electromagnetic form factors of baryons in nuclear medium

The electromagnetic structure of the baryons is modified in the nuclear medium. The modifications can be inferred from the comparison between the electromagnetic form factors in medium with the respective form factor in vacuum. Of particular interest is the ratio between the electric and magnetic form factors in medium ($G_E^*/G_M^*$) and vacuum ($G_E/G_M$) of the octet baryon. The deviation of the double ratios ($G_E^*/G_M^*)/(G_E/G_M)$ from unity measures the impact of the medium modification of the electromagnetic structure in a nuclear medium. Measurements of the double ratios $(G_E^*/G_M^*)/(G_E/G_M)$ for different nuclear densities may become available in a near future using the polarization-transfer method developed at Jefferson Lab. We present estimates of the double ratios of octet baryons based on a covariant constituent quark model, which takes into account pion cloud excitations of the baryon cores,for different nuclear densities. Our results manifest different features, namely, enhancement or quenching depending on the baryon flavor content.

hep-ph↗

arXiv2021

Charmonium in nuclear matter and nuclei

We present results for the $η_c$-nucleus bound state energies for various nuclei using an effective Lagrangians approach. The attractive potentials for the $η_c$ in the nuclear medium originate from the medium-modified intermediate $D D^{*}$ state in the $η_c$ self energy, using the local density approximation. Our results suggest that the $η_c$ should form bound states with all the nuclei considered

nucl-th↗

arXiv2021

\boldmath{$Υ$} and \boldmath{$η_b$} mass shifts in nuclear matter

We estimate the $Υ$, $η_b$ and $B^*$ meson mass shifts in symmetric nuclear matter. The interest is, whether the strengths of the bottomonium-(nuclear matter) and charmonium-(nuclear matter) interactions are similar or different. This is because, each ($J/Ψ,Υ$) and ($η_c,η_b$) meson group is usually assumed to have very similar properties based on the heavy charm and bottom quark masses. The estimate for the $Υ$ is made using an SU(5) effective Lagrangian and the anomalous coupling one, by studying the $BB$, $BB^*$, and $B^*B^*$ meson loop contributions for the self-energy. As for the $η_b$, we include the $BB^*$ and $B^*B^*$ meson loop contributions in the self-energy. The in-medium masses of the $B$ and $B^*$ mesons appearing in the self-energy are calculated by the quark-meson coupling model. An analysis on the $BB$, $BB^*$, and $B^*B^*$ meson loops in the $Υ$ mass shift is made by comparing with the corresponding $DD, DD^*$, and $D^*D^*$ meson loops for the $J/Ψ$ mass shift. Our prediction for the $η_b$ mass shift is made including only the lowest order $BB^*$ meson loop. The $Υ$ mass shift, with including only the $BB$ loop, is predicted to be -16 to -22 MeV at the nuclear matter saturation density using the $ΥBB$ coupling constant determined by the vector meson dominance model with the experimental data, while the $η_b$ mass shift is predicted to be -75 to -82 MeV with the SU(5) universal coupling constant determined by the $ΥBB$ coupling constant. Our results show an appreciable difference between the bottomonium-(nuclear matter) and charmonium-(nuclear matter) interaction strengths. We also study the $Υ$ and $η_b$ mass shifts in a heavy quark (heavy meson) symmetry limit.

hep-ph↗

arXiv2020

$η_{c}$-nucleus bound states

$η_c$-nucleus bound state energies are calculated for various nuclei. Essential input for the calculations, namely the medium-modified $D$ and $D^{*}$ meson masses, as well as the density distributions in nuclei, are calculated within the quark-meson coupling (QMC) model. The attractive potentials for the $η_c$ meson in the nuclear medium originate from the in-medium enhanced $DD^{*}$ loops in the $η_c$ self-energy. Our results suggest that the $η_c$ meson should form bound states with all the nuclei considered.

hep-ph↗

arXiv2020

Hyperon electromagnetic timelike elastic form factors at large $q^2$

We present estimates of the hyperon elastic form factors for the baryon octet and the $Ω^-$ baryon for large four-momentum transfer squared, $q^2$, in the timelike region ($q^2>0$). Experimentally, those form factors can be extracted from the $e^+ e^- \to B \bar B$ and $p \bar p \to B \bar B$ processes, where $B$ stands for a general baryon. Our results are based on calculations of the elastic electromagnetic form factors in the spacelike region ($Q^2 = - q^2 > 0$) within a covariant quark model. To connect the results in the spacelike region to those in the timelike region, we use asymptotic relations between the two regions which are constraints derived from analyticity and unitarity. We calculate the effective form factors $|G(q^2)|$ and compare them with the integrated cross section data $σ_{\rm Born} (q^2)$ from BaBar, BES III, and CLEO. The available data are at the moment restricted to $Λ$, $Σ^0$, $Σ^-$, $Ξ^-$, $Ξ^0$, and $Ω^-$ as well as to $e^+ e^- \to Λ\bar Σ^0 $ and $e^+ e^- \to Σ^0 \bar Λ$ reactions. Our results provide useful reference for future experiments and seem to indicate that the present data are still in the non-perturbative QCD region, while the onset for the asymptotic constraints from analyticity and unitarity happens much before the region of the perturbative QCD falloff of the form factors.

hep-ph↗

arXiv2019

Hadron properties in a nuclear medium and effective nuclear force from quarks: the quark-meson coupling model

We give a short review of the quark-meson coupling (QMC) model, the quark-based model of finite nuclei and hadron interactions in a nuclear medium, highlighting on the relationship with the Skyrme effective nuclear forces. The model is based on a mean field description of nonoverlapping nucleon MIT bags bound by the self-consistent exchange of Lorentz-scalar-isoscalar, Lorentz-vector-isoscalar, and Lorentz-vector-isovector meson fields directly coupled to the light quarks up and down. In conventional nuclear physics the Skyrme effective forces are very popular, but, there is no satisfactory interpretation of the parameters appearing in the Skyrme forces. Comparing a many-body Hamiltonian generated by the QMC model in the zero-range limit with that of the Skyrme force, it is possible to obtain a remarkable agreement between the Skyrme force and the QMC effective interaction. Furthermore, it is shown that 3-body and higher order N-body forces are naturally included in the QMC-generated effective interaction.

nucl-th↗

arXiv2019

Valence-quark distributions of pions and kaons in a nuclear medium

In-medium valence-quark distributions of $π^+$ and $K^+$ mesons in symmetric nuclear matter are studied by combining the Nambu--Jona-Lasinio model and the quark-meson coupling model. The in-medium properties of the current quarks, which are used as inputs for studying the in-medium pion and kaon properties in the Nambu--Jona-Lasinio model, are calculated within the quark-meson coupling model. The light-quark condensates, light-quark dynamical masses, pion and kaon decay constants, and pion- and kaon-quark coupling constants are found to decrease as nuclear density increases. The obtained valence quark distributions in vacuum for both the $π^+$ and $K^+$ could reasonably describe the available experimental data over a wide range of Bjorken-$x$. The in-medium valence $u$-quark distribution in the $π^+$ at $Q^2=16~\mbox{GeV}^2$ is found to be almost unchanged compared to the in-vacuum case. However, the in-medium to in-vacuum ratios of both the valence $u$-quark and valence $s$-quark distributions of the $K^+$ meson at $Q^2=16~\mbox{GeV}^2$ increase with nuclear matter density, but show different $x$-dependence. Namely, the ratio for the valence $u$-quark distribution increases with $x$, while that for the valence $s$ quark decreases with $x$. These features are enhanced at higher density regions.

hep-ph↗

arXiv2019

Electroweak properties of kaons in a nuclear medium

Kaon electroweak properties in symmetric nuclear matter are studied in the Nambu--Jona-Lasinio model using the proper-time regularization. The valence quark properties in symmetric nuclear matter are calculated in the quark-meson coupling model, and they are used as inputs for studying the in-medium kaon properties in the NJL model. We evaluate the kaon decay constant, kaon-quark coupling constant, and $K^+$ electromagnetic form factor by two different approaches. Namely, by two different ways of calculating the in-medium constituent quark masses of the light quarks. We predict that, in both approaches, the kaon decay constant and kaon-quark coupling constant decrease as nuclear density increases, while the $K^+$ charge radius increases by 20-25\% at normal nuclear density.

nucl-th↗

arXiv2019

$Z_c(4430)$ and $Z_c(4200)$ as triangle singularities

$Z_c(4430)$ discovered by the Belle and confirmed by the LHCb in $\bar{B}^0\toψ(2S)K^-π^+$ is generally considered to be a charged charmonium-like state that includes minimally two quarks and two antiquarks. $Z_c(4200)$ found in $\bar{B}^0\to J/ψK^-π^+$ by the Belle is also a good candidate of a charged charmonium-like state. We demonstrate that kinematical singularities in triangle loop diagrams induce a resonance-like behavior that can consistently explain the properties (mass, width, and Argand plot) of $Z_c(4430)$ and $Z_c(4200)$ from the experimental analyses. The triangle diagrams include only experimentally well-established hadrons. Applying this idea to $Λ_b^0\to J/ψpπ^-$, we also identify triangle singularities that behave like $Z_c(4200)$, but no triangle diagram is available for $Z_c(4430)$. This is consistent with the LHCb's finding that their description of the $Λ_b^0\to J/ψpπ^-$ data is significantly improved by including a $Z_c(4200)$ contribution while $Z_c(4430)$ seems to hardly contribute. Even though the proposed mechanisms have uncertainty in the absolute strengths which are currently difficult to estimate, they are certainly a compelling alternative to tetraquark-based interpretations of $Z_c(4430)$ and $Z_c(4200)$.

hep-ph↗

arXiv2019

Octet baryon electromagnetic form factor double ratios $(G_E^\ast/G_M^\ast)/(G_E/G_M)$ in a nuclear medium

The ratios of the baryon electric ($G_E$) to magnetic ($G_M$) form factors, $G_E/G_M$, can provide us with important information on the structure of baryons in vacuum as demonstrated in recent studies for the proton and neutron systems. It has been argued that the corresponding in-medium ratios, $G_E^\ast/G_M^\ast$, can also provide useful information on the electromagnetic structure of baryons in a nuclear medium. Although the ratios may not be measured directly in experiments except for the proton at present, the double ratios $(G_E^\ast/G_M^\ast)/(G_E/G_M)$ can be directly related to the polarization-transfer measurements of bound baryons. In the present work we estimate, for the first time, the double ratios $(G_E^\ast/G_M^\ast)/(G_E/G_M)$ for all the members of octet baryons in symmetric nuclear matter in the range $Q^2=0$--3 GeV$^2$, where $Q^2=- q^2$ with $q$ being the four-momentum transfer.

hep-ph↗

arXiv2019

Effects of medium modifications of nucleon form factors on neutrino scattering in dense matter

Effects of the in-medium modifications of nucleon form factors on neutrino interaction in dense matter are presented by considering both the weak and electromagnetic interactions of neutrinos with the constituents of the matter. A relativistic mean field and the quark-meson coupling models are respectively adopted for the effective nucleon mass and in-medium nucleon form factors. We calculate the cross-section of neutrino scattering as well as the neutrino mean free path. We found the cross sections of neutrino scattering in cold nuclear medium decreases when the in-medium modifications of the nucleon weak and electromagnetic form factors are taken into account.This reduction results in the enhancement of the neutrino mean free path, in particular at the baryon density of around a few times of the normal nuclear matter density.

nucl-th↗

arXiv2019

Pion structure in a nuclear medium

The structure and electroweak properties of the pion in symmetric nuclear matter are presented in the framework of the Nambu--Jona-Lasinio model. The pion is described as a bound state of a dressed quark-antiquark pair governed by the Bethe-Salpeter equation. For the in-medium current-light-quark properties we use the quark-meson coupling model, which describes successfully the properties of hadron in a nuclear medium. We found that the light-quark condensates, the pion decay constant and pion-quark coupling constant decrease with increasing nuclear matter density. We then predict the modifications of the charge radius of the charged pion in nuclear matter.

nucl-th↗

arXiv2019

In-medium properties of the low-lying bottom baryons in the quark-meson coupling model

In-medium properties of the low-lying baryons are studied in the quark-meson coupling (QMC) model, focusing on the $Σ_b$ and $Ξ_b$ baryons. It is predicted that the Lorentz-scalar effective mass of $Σ_b$ becomes smaller than that of $Ξ_b$ at moderate nuclear matter density, and as the density increases, namely, $m^*_{Σ_b} < m^*_{Ξ_b}$, although in vacuum $m_{Σ_b} > m_{Ξ_b}$. We also study the effects of the repulsive Lorentz-vector potentials on the excitation energies of these bottom baryons.

hep-ph↗

arXiv2019

Description of the recently observed hypernucleus $^{15}{\!\!\!_{Ξ^-}}$C within a quark-meson coupling model

We investigate within a quark-meson coupling (QMC) model, the structure of the bound $Ξ^-$ hypernucleus $^{15}{\!\!\!_{Ξ^-}}$C ($^{14}$N + $Ξ^-$), which has been observed in a recent analysis of the KEK-E373 experiment. In the QMC model, light quarks in nonoverlapping nucleon and $Ξ^-$ bags interact self-consistently with isoscalar-scalar ($σ$), isoscalar-vector ($ω$), and isovector-vector ($ρ$) mesons in the mean field approximation. The parameters of the model (quark-meson coupling constants and masses) are mostly fixed from the nuclear matter saturation properties. The QMC model closely reproduces the separation energies of the two $Ξ^-$ hyperon states in $^{15}{\!\!\!_{Ξ^-}}$C reported in the KEK-E373 analysis, and identifies their quantum numbers. We also make predictions for the cross sections for the production of the $^{15}{\!\!\!_{Ξ^-}}$C hypernuclear specta in the ($K^-, K^+$) reaction on a $^{15}$O target within a covariant effective Lagrangian model using the $Ξ^-$ bound state spinors obtained within the same QMC model.

nucl-th↗

arXiv2019

$Φ$ and $J/Ψ$ Mesons in Cold Nuclear Matter

We present $Φ$- and $J/Ψ$--nuclear bound state energies and absorption widths for some selected nuclei, using potentials in the local density approximation computed from an effective Lagrangian approach combined with the quark-meson coupling model. Our results suggest that these mesons should form bound states with all the nuclei considered provided that these mesons are produced in nearly recoilless kinematics.

hep-ph↗

arXiv2019

In-medium properties of the low-lying strange, charm, and bottom baryons in the quark-meson coupling model

In-medium properties of the low-lying strange, charm, and bottom baryons in symmetric nuclear matter are studied in the quark-meson coupling (QMC) model. Results for the Lorentz-scalar effective masses, mean field potentials felt by the light quarks in the baryons, in-medium bag radii, and the lowest mode bag eigenvalues are presented for those calculated using the updated data. This study completes the in-medium properties of the low-lying baryons in symmetric nuclear matter in the QMC model, for the strange, charm and bottom baryons which contain one or two strange, one charm or one bottom quarks, as well as at least one light quark. Highlight is the prediction of the bottom baryon Lorentz-scalar effective masses, namely, the Lorentz-scalar effective mass of $Σ_b$ becomes smaller than that of $Ξ_b$ at moderate nuclear matter density, $m^*_{Σ_b} < m^*_{Ξ_b}$, although in vacuum $m_{Σ_b} > m_{Ξ_b}$. We study further the effects of the repulsive Lorentz-vector potentials on the excitation (total) energies of these bottom baryons.

hep-ph↗