arXiv subjects

T. T. Takahashi

Publications and source records attributed to T. T. Takahashi.

At least 19 recordsLinked to original sources

arXiv2020

Stable double-heavy tetraquarks: spectrum and structure

Bound states of double-heavy tetraquarks are studied in a constituent quark model. Two bound states are found for isospin and spin-parity I(J^P ) = 0(1^+) in the bb\bar{u}\bar{d} channel. One is deeply bound and compact made of colored diquarks, while the other is shallow and extended as a BB^* molecule. The former agrees well with lattice QCD results. A systematic decrease in the binding energy is seen by replacing one of the heavy quarks to a lighter one. Altogether we find ten bound states. It is shown for the first time that hadrons with totally different natures emerge from a single Hamiltonian.

nucl-th↗

arXiv2018

Radiative transitions of doubly charmed baryons in lattice QCD

We evaluate the spin-$3/2 \to$ spin-$1/2$ electromagnetic transitions of the doubly charmed baryons on 2+1 flavor, $32^3 \times 64$ PACS-CS lattices with a pion mass of $156(9)$ MeV/c$^2$. A relativistic heavy quark action is employed to minimize the associated systematic errors on charm-quark observables. We extract the magnetic dipole, $M1$, and the electric quadrupole, $E2$, transition form factors. In order to make a reliable estimate of the $M1$ form factor, we carry out an analysis by including the effect of excited-state contributions. We find that the $M1$ transition is dominant and light degrees of freedom ($u/d$- or $s$-quark) play the leading role. $E2$ form factors, on the other hand, are found to be negligibly small, which in turn, have minimal effect on the helicity and transition amplitudes. We predict the decay widths and lifetimes of $Ξ_{cc}^{\ast +,++}$ and $Ω_{cc}^{\ast +}$ based on our results. Finite size effects on these ensembles are expected to be around 1\%. Differences in kinematical and dynamical factors with respect to the $Nγ\toΔ$ transition are discussed and compared to non-lattice determinations as well keeping possible systematic artifacts in mind. A comparison to $Ω_c γ\rightarrow Ω_c^\ast$ transition and a discussion on systematic errors related to the choice of heavy quark action are also given. Results we present here are particularly suggestive for experimental facilities such as LHCb, PANDA, Belle II and BESIII to search for further states.

hep-lat↗

arXiv2017

$Ξ_c γ\rightarrowΞ^\prime_c$ transition in lattice QCD

We evaluate the electromagnetic $Ξ_c γ\rightarrowΞ_c^\prime$ transition on 2+1 flavor lattices corresponding to a pion mass of $\sim 156$ MeV. We extract the magnetic Sachs and Pauli form factors which give the $Ξ_c$-$Ξ_c^\prime$ transition magnetic moment and the decay rates of $Ξ_c^\prime$ baryons. We did not find a signal for the magnetic form factor of the neutral transition $Ξ_c^0 γ\rightarrowΞ_c^{\prime 0}$, which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of $Ξ_c$ and $Ξ_c^\prime$ baryons, which give an insight to the dynamics of $u/d$, $s$ and $c$ quarks having masses at different scales.

hep-lat↗

arXiv2016

$Λ_cΣ_cπ$ coupling and $Σ_c \rightarrowΛ_c π$ decay in lattice QCD

We evaluate the $Λ_cΣ_cπ$ coupling constant ($G_{Λ_c Σ_c π}$) and the width of the strong decay $Σ_c \rightarrowΛ_c π$ in 2+1 flavor lattice QCD on four different ensembles with pion masses ranging from 700 MeV to 300 MeV. We find $G_{Λ_c Σ_c π}=18.332(1.476)_{\rm{stat.}}(2.171)_{\rm{syst.}}$ and the decay width $Γ(Σ_c \rightarrowΛ_c π)=1.65(28)_{\rm{stat.}}(30)_{\rm{syst.}}$~MeV on the physical quark-mass point, which is in agreement with the recent experimental determination.

hep-lat↗

arXiv2015

A look inside charmed-strange baryons from lattice QCD

The electromagnetic form factors of the spin-3/2 $Ω$ baryons, namely $Ω$, $Ω_c^\ast$, $Ω_{cc}^\ast$ and $Ω_{ccc}$, are calculated in full QCD on $32^3\times 64$ PACS-CS lattices with a pion mass of 156(9) MeV. The electric charge radii and magnetic moments from the $E0$ and $M1$ multipole form factors are extracted. Results for the electric quadrupole form factors, $E2$, are also given. Quark sector contributions are computed individually for each observable and then combined to obtain the baryon properties. We find that the charm quark contributions are systematically smaller than the strange-quark contributions in the case of the charge radii and magnetic moments. $E2$ moments of the $Ω_{cc}^\ast$ and $Ω_{ccc}$ provide a statistically significant data to conclude that their electric charge distributions are deformed to an oblate shape. Properties of the spin-1/2 $Ω_c$ and $Ω_{cc}$ baryons are also computed and a thorough comparison is given. This complete study gives valuable hints about the heavy-quark dynamics in charmed hadrons.

hep-lat↗

arXiv2014

Electromagnetic structure of charmed baryons in Lattice QCD

As a continuation of our recent work on the electromagnetic properties of the doubly charmed $Ξ_{cc}$ baryon, we compute the charge radii and the magnetic moments of the singly charmed $Σ_c$, $Ω_c$ and the doubly charmed $Ω_{cc}$ baryons in 2+1 flavor Lattice QCD. In general, the charmed baryons are found to be compact as compared to the proton. The charm quark acts to decrease the size of the baryons to smaller values. We discuss the mechanism behind the dependence of the charge radii on the light valence- and sea-quark masses. The magnetic moments are found to be almost stable with respect to changing quark mass. We investigate the individual quark sector contributions to the charge radii and the magnetic moments. The magnetic moments of the singly charmed baryons are found to be dominantly determined by the light quark and the role of the charm quark is significantly enhanced for the doubly charmed baryons.

hep-lat↗

arXiv2013

Electromagnetic properties of doubly charmed baryons in Lattice QCD

We compute the electromagnetic properties of Ξ_cc baryons in 2+1 flavor Lattice QCD. By measuring the electric charge and magnetic form factors of Ξ_cc baryons, we extract the magnetic moments, charge and magnetic radii as well as the Ξ_cc Ξ_cc ρcoupling constant, which provide important information to understand the size, shape and couplings of the doubly charmed baryons. We find that the two heavy charm quarks drive the charge radii and the magnetic moment of Ξ_cc to smaller values as compared to those of, e.g., the proton.

hep-lat↗

arXiv2013

Vector and axial-vector couplings of D and D* mesons in 2+1 flavor Lattice QCD

Using the axial-vector coupling and the electromagnetic form factors of the D and D* mesons in 2+1 flavor Lattice QCD, we compute the D*Dπ, DDρand D*D*ρcoupling constants, which play an important role in describing the charm hadron interactions in terms of meson-exchange models. We also extract the charge radii of D and D* mesons and determine the contributions of the light and charm quarks separately.

hep-lat↗

arXiv2011

Lattice QCD Study for Confinement in Hadrons

We study three subjects on quark confinement in hadrons in SU(3)$_{\rm c}$ lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential is well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. We also study the multi-quark (4Q, 5Q) potentials in lattice QCD, and find that they are well described by the one-gluon-exchange (OGE) Coulomb plus string-theoretical linear potential, which supports the {\it infrared string picture} even for the multi-quarks. The second subject is a lattice-QCD determination of the relevant gluonic momentum component for confinement. The string tension (confining force) is found to be almost unchanged even after cutting off the high-momentum gluon component above 1.5GeV in the Landau gauge. In fact, {\it quark confinement originates from the low-momentum gluon below about 1.5GeV.} Finally, we consider a possible gauge of QCD for the quark potential model, by investigating "instantaneous inter-quark potential" in generalized Landau gauge, which describes a continuous change from the Landau gauge to the Coulomb gauge.

hep-lat↗

arXiv2010

Chaotic behavior in classical Yang-Mills dynamics

Understanding the underlying mechanisms causing rapid thermalization deduced for high-energy heavy ion collisions is still a challenge. To estimate the thermalization time, entropy growth for classical Yang-Mills theories is studied, based on the determination of Lyapunov exponents. Distinct regimes for short, medium and long sampling times are characterized by different properties of their spectrum of Lyapunov exponents. Clarifying the existence of these regimes and their implications for gauge-field dynamics is one of the results of this contribution. As a phenomenological application we conclude that for pure gauge theories with random initial conditions thermalization occurs within few fm/c, an estimate which can be reduced by the inclusion of fermions, specific initial conditions, etc.

hep-ph↗

arXiv2010

Axial Charges of Octet Baryons in Two-flavor Lattice QCD

We evaluate the strangeness-conserving $N N$, $ΣΣ$, $ΞΞ$, $ΛΣ$ and the strangeness-changing $ΛN$, $ΣN$, $ΛΞ$, $ΣΞ$ axial charges in lattice QCD with two flavors of dynamical quarks and extend our previous work on pseudoscalar-meson-octet-baryon coupling constants so as to include $πΞΞ$, $KΛΞ$ and $KΣΞ$ coupling constants. We find that the axial charges have rather weak quark-mass dependence and the breaking in SU(3)-flavor symmetry is small at each quark-mass point we consider.

hep-lat↗

arXiv2009

Pseudoscalar-meson--octet-baryon coupling constants in two-flavor lattice QCD

We evaluate the $πN!N$, $πΣΣ$, $πΛΣ$, $KΛN$ and $K ΣN $ coupling constants and the corresponding monopole masses in lattice QCD with two flavors of dynamical quarks. The parameters representing the SU(3)-flavor symmetry are computed at the point where the three quark flavors are degenerate at the physical $s$-quark mass. In particular, we obtain $α\equiv F/(F+D)=0.395(6)$. The quark-mass dependences of the coupling constants are obtained by changing the $u$- and the $d$-quark masses. We find that the SU(3)-flavor parameters have weak quark-mass dependence and thus the SU(3)-flavor symmetry is broken by only a few percent at each quark-mass point we consider.

hep-lat↗

arXiv2008

Inter-Quark Potentials in Baryons and Multi-Quark Systems in QCD

We perform the first studies of various inter-quark potentials in SU(3)$_{\rm c}$ lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential $V_{\rm 3Q}$ is well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. Quark confinement mechanism in baryons is also investigated in maximally-Abelian projected QCD. We next study the multi-quark potentials $V_{n{\rm Q}}$ ($n$=4,5) in SU(3)$_{\rm c}$ lattice QCD, and find that they are well described by the one-gluon-exchange Coulomb plus multi-Y type linear potential, which supports the flux-tube picture even for the multi-quarks. Finally, we study the heavy-heavy-light quark (QQq) potential both in lattice QCD and in a lattice-QCD-based quark model.

hep-ph↗

arXiv2007

Lattice QCD study of $g_A^{N^N^}$ with two flavors of dynamical quarks

We report the first lattice QCD result of the axial charge of N(1535), $g_A^{N^*N^*}$. The measurement is performed with two flavors of dynamical quarks employing the renormalization-group improved gauge action at $β$=1.95 and the mean-field improved clover quark action with the hopping parameters, $κ$=0.1375, 0.1390 and 0.1400. In order to avoid the signal contaminations by N(1650) lying just 100 MeV above N(1535), we construct 2$\times$2 correlation matrices and diagonalize them so that clear signal separation can be found. The wraparound contributions in the correlator, which can be another source of signal contamination, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N(1535) takes small values as $g_A^{N^*N^*}\sim 0.2$, independent of quark masses, in the pion-mass range of 0.7 to 1.1 GeV.

hep-lat↗

arXiv2007

Scalar-Quark Systems and Chimera Hadrons in SU(3)_c Lattice QCD

Light scalar-quarks ϕ(colored scalar particles or idealized diquarks) and their color-singlet hadronic states are studied with quenched SU(3)_c lattice QCD in terms of mass generation in strong interaction without chiral symmetry breaking. We investigate ``scalar-quark mesons'' ϕ^\dagger ϕand ``scalar-quark baryons'' ϕϕϕwhich are the bound states of scalar-quarks ϕ. We also investigate the bound states of scalar-quarks ϕand quarks ψ, i.e., ϕ^\dagger ψ, ψψϕand ϕϕψ, which we name ``chimera hadrons''. All the new-type hadrons including ϕare found to have a large mass even for zero bare scalar-quark mass m_ϕ=0 at a^{-1}\simeq 1GeV. We find that the constituent scalar-quark and quark picture is satisfied for all the new-type hadrons. Namely, the mass of the new-type hadron composed of m ϕ's and n ψ's, M_{{m}ϕ+{n}ψ}, satisfies M_{{m}ϕ+{n}ψ}\simeq {m} M_ϕ+{n} M_ψ, where M_ϕand M_ψare the constituent scalar-quark and quark mass, respectively. M_ϕat m_ϕ=0 estimated from these new-type hadrons is 1.5-1.6GeV, which is larger than that of light quarks, M_ψ\simeq 400{\rm MeV}. Therefore, in the systems of scalar-quark hadrons and chimera hadrons, scalar-quarks acquire large mass due to large quantum corrections by gluons. Together with other evidences of mass generations of glueballs and charmonia, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects.

hep-lat↗

arXiv2006

Bound States of (Anti-)Scalar-Quarks in SU(3)_c Lattice QCD

Light scalar-quarks ϕ(colored scalar particles or idealized diquarks) and their color-singlet hadronic states are studied with quenched SU(3)_c lattice QCD in terms of mass generation. We investigate ``scalar-quark mesons'' ϕ^\dagger ϕand ``scalar-quark baryons'' ϕϕϕas the bound states of scalar-quarks ϕ. We also investigate the bound states of scalar-quarks ϕand quarks ψ, i.e., ϕ^\dagger ψ, ψψϕand ϕϕψ, which we name ``chimera hadrons''. All the new-type hadrons including ϕare found to have a large mass due to large quantum corrections by gluons, even for zero bare scalar-quark mass m_ϕ=0 at a^{-1}\sim 1{\rm GeV}. We conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects.

hep-lat↗

arXiv2006

Nuclear force in Lattice QCD

We perform the quenched lattice QCD analysis on the nuclear force (baryon-baryon interactions). We employ $20^3\times 24$ lattice at $β=5.7$ ($a\simeq 0.19$ fm) with the standard gauge action and the Wilson quark action with the hopping parameters $κ=0.1600, 0.1625, 0.1650$, and generate about 200 gauge configurations. We measure the temporal correlators of the two-baryon system which consists of heavy-light-light quarks. We extract the inter-baryon force as a function of the relative distance $r$. We also evaluate the contribution to the nuclear force from each ``Feynman diagram'' such as the quark-exchange diagram individually, and single out the roles of Pauli-blocking effects or quark exchanges in the inter-baryon interactions.

hep-lat↗

arXiv2005

Tetraquark and Pentaquark Systems in Lattice QCD

Motivated by the recent experimental discoveries of multi-quark candidates, e.g., the $Θ^+(1540)$, we study multi-quark systems in lattice QCD. First, we perform accurate mass measurements of low-lying 5Q states with $J=1/2$ and I=0 in both positive- and negative-parity channels in anisotropic lattice QCD. The lowest positive-parity 5Q state is found to have a large mass of about 2.24GeV after the chiral extrapolation. To single out the compact 5Q state from $NK$ scattering states, we develop a new method with the hybrid-boundary condition (HBC), and find no evidence of the compact 5Q state below 1.75GeV in the negative-parity channel. Second, we perform the first study of the multi-quark potential in lattice QCD to clarify the inter-quark interaction in multi-quark systems. The 5Q potential $V_{\rm 5Q}$ for the QQ-${\rm \bar{Q}}$-QQ system is found to be well described by the ``OGE Coulomb plus multi-Y Ansatz": the sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term based on the flux-tube picture. The 4Q potential $V_{\rm 4Q}$ for the QQ-${\rm \bar{Q}\bar{Q}}$ system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ and $\rm \bar Q \bar Q$ are well separated. The 4Q system is described as a "two-meson" state with disconnected flux tubes, when the nearest quark and antiquark pair is spatially close. We observe a lattice-QCD evidence for the ``flip-flop'', i.e., the flux-tube recombination between the connected 4Q state and the ``two-meson'' state. On the confinement mechanism, the lattice QCD results indicate the flux-tube-type linear confinement in multi-quark hadrons.

hep-ph↗