arXiv subjects

Masayasu Harada

Publications and source records attributed to Masayasu Harada.

At least 55 records · Page 3Linked to original sources

arXiv2019

Heavy quark spin multiplet structure of $P_c$-like pentaquark as P-wave hadronic molecular state

We study the heavy quark spin (HQS) multiplet structure of P-wave $Q\bar{Q}qqq$-type pentaquarks treated as molecules of a heavy meson and a heavy baryon. We define the light-cloud spin (LCS) basis decomposing the meson-baryon spin wavefunction into the LCS and HQS parts. Introducing the LCS basis, we find HQS multiplets classified by the LCS; five HQS singlets, two HQS doublets, and three HQS triplets. We construct the one-pion exchange potential respecting the heavy quark spin and chiral symmetries to demonstrate which HQS multiplets are realized as a bound state. By solving the coupled channel Schrödinger equations, we study the heavy meson-baryon systems with $I=1/2$ and $J^P=(1/2^+, 3/2^+, 5/2^+, 7/2^+)$. The bound states which have same LCS structure are degenerate at the heavy quark limit, and the degeneracy is resolved for finite mass. This HQS multiplet structure will be measured in the future experiments.

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arXiv2019

Constraint to chiral invariant masses of nucleons from GW170817 in an extended parity doublet model

We construct nuclear matter based on an extended parity doublet model including four light nucleons $N(939)$, $N(1440)$, $N(1535)$, and $N(1650)$. We exclude some values of the chiral invariant masses by requiring the saturation properties of normal nuclear matter; saturation density, binding energy, incompressibility, and symmetry energy. We find further constraint to the chiral invariant masses from the tidal deformability determined by the observation of the gravitational waves from neutron star merger GW170817. Our result shows that the chiral invariant masses are larger than about $600\,$MeV. We also give some predictions on the symmetry energy and the slope parameters in the high density region, which will be measured in future experiments.

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arXiv2018

Chiral partner structure of light nucleons in an extended parity doublet model

We study chiral partner structure of four light nucleons, $N(939)$, $N(1440)$, $N(1535)$ and $N(1650)$ using an effective chiral model based on the parity doublet structure. In our model we introduce four chiral representations, $({\bf 1},{\bf 2})$, $({\bf 2},{\bf 1})$, $({\bf 2},{\bf 3})$ and $({\bf 3},{\bf 2})$ under ${\rm SU}(2)_{\rm L} \otimes {\rm SU}(2)_{\rm R}$ symmetry. We determine the model parameters by fitting them to available experimental values of masses, widths and the axial charge of $N(939)$ together with the axial charges of $N(1535)$ and $N(1650)$ by lattice analyses. We find five groups of solutions: In a group the chiral partner to $N(939)$ is $N(1440)$ having small chiral invariant mass. In another group, the chiral partner is a mixture of $N(1535)$ and $N(1650)$ having a large chiral invariant mass. We claim that off-diagonal elements of axial-charge matrix can be used for distinguishing these groups. We also discuss changes of masses associated with chiral symmetry restoration, which could emerge in high density matter.

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arXiv2018

Dual chiral density waves in nuclear matter

We study inhomogeneous chiral phases in nuclear matter using a hadronic model with the parity doublet structure. With an extended ansatz for the dual chiral density wave off the chiral limit, we numerically determine the phase structure. A new type of dual chiral density wave where the condensate has nonvanishing space average is confirmed and it comes to occupy a wide range of low density region as the chiral invariant mass parameter is lowered.

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arXiv2018

Heavy quark spin multiplet structure of $\bar{P}^{()}Σ_Q^{()}$ molecular states

We study the structure of heavy quark spin (HQS) multiplets for heavy meson-baryon molecular states in a coupled system of $\bar{P}^{(*)}Σ_{Q}^{(*)}$, with constructing the one-pion exchange potential with S-wave orbital angular momentum. Using the light cloud spin basis, we find that there are four types of HQS multiplets classified by the structure of heavy quark spin and light cloud spin. The multiplets which have attractive potential are determined by the sign of the coupling constant for the heavy meson-pion interactions. Furthermore, the difference in the structure of light cloud spin gives the restrictions of the decay channel, which implies that the partial decay width has the information for the structure of HQS multiplets. This behavior is more likely to appear in hidden-bottom sector than in hidden-charm sector.

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arXiv2018

Analysis of $Λ_c(2595)$, $Λ_c(2625)$, $Λ_b(5912)$, $Λ_b(5920)$ based on a chiral partner structure

We construct an effective hadronic model including $Λ_c(2595)$, $Λ_c(2625)$, $Λ_b(5912)$ and $Λ_b(5920)$ regarding them as chiral partners to $Σ_c(2455)$, $Σ_c(2520)$, $Σ_b$ and $Σ_b^\ast$, respectively, with respecting the chiral symmetry and heavy-quark spin-flavor symmetry. We determine the model parameters from the experimental data for relevant masses and decay widths of $Σ_c^{(\ast)}$ and $Λ_c(2595)$. Then, we study the decay widths of $Λ_c(2625)$, $Λ_b(5912)$ and $Λ_b(5920)$. We find that, although the decay of $Λ_c(2595)$ is dominated by the resonant contribution through $Σ_c(2455)$, non-resonant contributions are important for $Λ_c(2625)$, $Λ_b(5912)$ and $Λ_b(5920)$, which reflects the chiral partner structure. We also study the radiative decays of the baryons, and show that each of their widths is determined from the radiative decay width of their chiral partners.

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arXiv2018

A novel Dual Chiral Density Wave in nuclear matter based on a parity doublet structure

We study the Dual Chiral Density Wave (DCDW) in nuclear matter using a hadronic model with the parity doublet structure. We first extend the ordinary DCDW ansatz so as to incorporate the effect of an explicit chiral symmetry breaking. Then via numerically evaluating and minimizing the effective potential, we determine the phase structure. We find, in addition to the ordinary DCDW phase where the space average of the chiral condensate vanishes, a new DCDW phase (sDCDW) with a nonvanishing space average depending on the value of the chiral invariant mass parameter.

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arXiv2017

Chiral partner structure of doubly heavy baryons with heavy quark spin-flavor symmetry

The spectrum of the doubly heavy baryons is estimated with respect to the new observation from the LHCb collaboration [Aaij:2017ueg] by using the chiral partner structure and heavy quark spin-flavor symmetry. The effects of heavy quark flavor symmetry breaking and light quark flavor symmetry are considered. The mass splitting of doubly heavy baryons with the same spin but opposite parity arises from the generalized Goldberger-Treiman relation. The intermultiplet one-pion transition and intramultiplet radiative transitions are also be estimated.

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arXiv2017

Relation between the mass modification of the heavy-light mesons and the chiral symmetry structure in dense matter

We point out that the study of the density dependences of the masses of heavy-light mesons give some clues to the chiral symmetry structure in nuclear matter. We include the omega meson effect as well as the sigma meson effect at mean field level on the density dependence of the masses of heavy-light mesons with chiral partner structure. It is found that the omega meson affects the masses of the heavy-light mesons and their antiparticles in the opposite way, while it affects the masses of chiral partners in the same way. This is because the omega meson is sensitive to the baryon number of the light degrees included in the heavy-light mesons. We also show that the mass difference between chiral partners is proportional to the mean field of sigma, reflecting the partial restoration of chiral symmetry in the nuclear matter. In addition to the general illustration of the density dependence of the heavy-light meson masses, we consider two concrete models for nuclear matter, the parity doublet model and skyrmion crystal model in the sense of mean field approximation.

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arXiv2017

Hidden Charm Pentaquark $P_c(4380)$ and Doubly Charmed Baryon $Ξ_{cc}^*(4380)$ as Hadronic Molecule States

We study hadronic molecular states in a coupled system of $J/ψN - Λ_c\bar{D}^{(*)} - Σ_c^{(*)}\bar{D}^{(*)}$ in $I(J^P) = \frac{1}{2}(\frac{3}{2}^-)$ channel, using the complex scaling method combined with the Gaussian expansion method. We construct the potential including one pion exchange and one $D^{(*)}$ meson exchange with $S$-wave orbital angular momentum. We find that the both mass and width of the pentaquark $P_c(4380)$ can be reproduced within a reasonable parameter region, and that its main decay mode is $Λ_c\bar{D}^*$. We extend our analysis to a coupled system of $Λ_c D^{(*)} - Σ_c^{(*)}D^{(*)}$ in $I(J^P) = \frac{1}{2}(\frac{3}{2}^-)$ channel. We find that there exists a doubly charmed baryon of $ccqq\bar{q}$ type as a hadronic molecule, the mass and width of which are quite close to those of $P_c(4380)$.

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arXiv2017

Catalysis of partial chiral symmetry restoration by Delta matter

We study the phase structure of dense hadronic matter including $Δ(1232)$ as well as N(939) based on the parity partner structure, where the baryons have their chiral partners with a certain amount of chiral invariant masses. We show that, in symmetric matter, $Δ$ enters into matter in the density region of about one to four times of normal nuclear matter density, $ρ_B \sim 1 - 4ρ_0$. The onset density of $Δ$ matter depends on the chiral invariant mass of $Δ$, $m_{\Delta0}$: The lager $m_{\Delta0}$, the bigger the onset density. The $Δ$ matter of $ρ_B \sim 1 - 4ρ_0$ is unstable due to the existence of $Δ$, and the stable $Δ$-nucleon matter is realized at about $ρ_B \sim 4ρ_0$, i.e., the phase transition from nuclear matter to $Δ$-nucleon matter is of first order for small $m_{\Delta0}$, and it is of second order for large $m_{\Delta0}$. We find that, associated with the phase transition, the chiral condensate changes very rapidly, i.e., the chiral symmetry restoration is accelerated by Δmatter. As a result of the accelerations, there appear $N^*$(1535) and $Δ$(1700), which are the chiral partners to N(939) and $Δ$(1232), in high density matter, signaling the partial chiral symmetry restoration. Furthermore, we find that complete chiral symmetry restoration itself is delayed by $Δ$ matter. We also calculate the effective masses, pressure and symmetry energy to study how the transition to $Δ$ matter affects such physical quantities. We observe that the physical quantities change drastically at the transition density.

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arXiv2017

Charged pions tagged with polarized photons probing strong CP violation in a chiral-imbalance medium

It is expected that in a hot QCD system, a local parity-odd domain can be produced due to nonzero chirality, which is induced from the difference of winding numbers carried by the gluon topological configuration (QCD sphaleron). This local domain is called the chiral-imbalance medium characterized by nonzero chiral chemical potential, which can be interpreted as the time variation of the strong CP phase. We find that the chiral chemical potential generates the parity breaking term in the electromagnetic form factor of charged pions. Heavy ion collision experiments could observe the phenomenological consequence of this parity-odd form factor through the elastic scattering of a pion and a photon in the medium. Then we quantify the asymmetry rate of the parity violation by measuring the polarization of the photon associated with the pion, and discuss how it could be measured in a definite lab frame. We roughly estimate the typical size of the asymmetry, just by picking up the pion resonant process, and find that the signal can be sufficiently larger than possible background events from parity-breaking electroweak process. Our findings might provide a novel possibility to make a manifest detection for the remnant of the strong CP violation.

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arXiv2017

Spectral functions for $\bar{D}$ meson and $\bar{D}_0^*$ meson in nuclear matter with partial restoration of chiral symmetry

We investigate the in-medium masses of a $\bar{D} (0^-)$ meson and a $\bar{D}_0^* (0^+)$ meson and spectral functions for $\bar{D}$ and $\bar{D}_0^*$ meson channels in nuclear matter. These mesons are introduced as chiral partner in the chiral symmetry broken vacuum, hence they are useful to explore the partial restoration of the broken chiral symmetry in nuclear matter. We consider the linear sigma model to describe the chiral symmetry breaking. Our study shows that the loop corrections to $\bar{D}$ and $\bar{D}_0^*$ meson masses provide a smaller mass splitting at finite density than that in vacuum, whose result indicates a tendency of the restoration of the chiral symmetry. We investigate also the spectral function for $\bar{D}_0^*$ meson channel, and find three peaks. The first peak which corresponds to the resonance of $\bar{D}_0^*$ meson is broadened by collisions with nucleons in medium, and the peak position shifts to lower mass due to the partial restoration of chiral symmetry as the density increases. The second peak is identified as a threshold enhancement which shows a remarkable enhancement as the density increase. The third peak is Landau damping. The obtained properties of $\bar{D}$ and $\bar{D}_0^*$ mesons in nuclear matter will provide useful information for experiments.

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arXiv2016

Relations among pionic decays of spin-1 mesons from an SU(4)$\times$U(1) emergent symmetry in QCD

Motivated by recent results by lattice analysis, we assume that the spin-1 mesons of $\left( ρ, ω, a_1, ρ', ω', b_1, f_1, h_1\right)$ make a representation of $\mathbf{16}$ of U(4) emergent symmetry in two-flavor QCD when the chiral symmetry is not broken. We study the decay properties of the spin-1 mesons by using a chiral model with an SU(4)$\times$U(1) hidden local symmetry. We first show that, since the SU(4) symmetry is spontaneously broken together with the chiral symmetry, each coupling of the interaction among one pion and two spin-1 mesons is proportional to the mass difference of the relevant spin-1 mesons similarly to the Goldberger-Treiman relation. In addition, some of one-pion couplings are related with each other by the SU(4) symmetry. We further show that there is a relation among the mass of $ρ'$ meson, the $ρ'ππ$ coupling and the $ρ'$-photon mixing strength as well as the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin relation for the $ρ$ meson. From the relations, we give numerical predictions such as ratios of the spin-1 meson decay widths, which are compared with future experiments for testing the existence of the U(4) emergent symmetry.

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arXiv2016

Coupled channel analysis of molecule picture of $P_{c}(4380)$

We construct a potential obtained by one-pion exchange for the coupled channel $Σ_c^\ast$$\bar{D}$-$Σ_c$$\bar{D}^\ast$, and solve the coupled Schrödinger equations to determine the binding energy. We find that there exists one or two bound states with the binding energy of several MeV below the threshold of $Σ_c^\ast$ and $\bar{D}$, dominantly made from a $Σ_c^\ast$ baryon and a $\bar{D}$ meson, with the size of about $1.5$fm for wide parameter region. We also study the pentaquark states including a $b$ quark and/or an anti-$b$ quark. We show that there exist pentaquarks including $c\bar{b}$, $b\bar{c}$ and $b\bar{b}$, all of which lie at about $10$MeV below the corresponding threshold and have size of about $1.5$fm.

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arXiv2016

Lecture notes on the Skyrme model

This lecture provides a pedagogical instruction to the basic concepts of the Skyrme model and its some applications. As the preliminary for understanding the Skyrme model, we first briefly explain the large $N_c$ expansion, chiral symmetry and its breaking. Next we give a brief review of nonlinear sigma model including the power counting scheme of the chiral perturbation theory, starting from the linear sigma model. We then give an exhaust explanation of the Skyrme model and its applications. After the presentation of the Skyrme model for baryons in free space, we introduce how to study the baryonic matter and medium modified hadron properties by using the Skyrme model. Finally we discuss a way to incorporate the lowest-lying vector mesons into the Skyrme model based on the hidden local symmetry. Some possible further developments are also covered.

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arXiv2016

Appearance of novel modes of $\bar{D}$ mesons in the Dual Chiral Density Wave

We calculate dispersion relations for $\bar{D}(0^-)$, $\bar{D}^*(1^-)$, $\bar{D}_0^*(0^+)$ and $\bar{D}_1(1^+)$ mesons in the Dual Chiral Density Wave (DCDW) where the chiral symmetry is spontaneously broken by inhomogeneous chiral condensate. Employing the Bloch's theorem, we show that all the modes have opposite group velocity to the momentum in the low-momentum region and the energy is minimized at non-zero momentum. Furthermore, the magnitude of momentum which realizes the minimum energy is equal to the wave number of the density wave.

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arXiv2016

Fractionized Skyrmions in Dense Compact-Star Matter

The hadronic matter described as a skyrmion matter embedded in an FCC crystal is found to turn into a half-skyrmion matter with vanishing (in the chiral limit) quark condensate and {\it non-vanishing} pion decay constant {$f_π$} at a density $n_{1/2}$ lower than or near the critical density $n_c$ at which hadronic matter changes over to a chiral symmetry restored phase with possibly deconfined quarks. When hidden local gauge fields and a dilaton scalar of spontaneously broken scale symmetry with decay constant $f_χ$ are incorporated, this half-skyrmion phase is characterized by $f_χ\approx f_π\neq 0$ with the hidden gauge coupling $g\neq 0$ but $\ll 1$. While chiral symmetry is restored {\it globally} in this region in the sense that space-averaged, $\la\bar{q}q\ra$ vanishes, quarks are still confined in massive hadrons and massless pions. This phase is shown to play a crucial role in the model for a smooth transition from a soft EoS at low density to a stiffer EoS at high density, the changeover taking place at $n_{1/2} \sim 2n_0$. It resembles the "quarkyonic phase" predicted in large $N_c$ QCD and represents the "hadronic freedom" regime which figures as a doorway to chiral restoration. The fractionization of skyrmion matter into half-skyrmion matter has a tantalizing analogy to what appears to happen in condensed matter in (2+1) dimensions where half-skyrmions or "merons" enter as relevant degrees of freedom at the interface.

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