arXiv subjects

Noriyoshi Ishii

Publications and source records attributed to Noriyoshi Ishii.

At least 73 records · Page 4Linked to original sources

arXiv2007

Tetra-Quark Resonances in Lattice QCD

We study $qq \bar q \bar q$-type four-quark (4Q) systems in SU(3)$_c$ anisotropic quenched lattice QCD, using the $O(a)$-improved Wilson (clover) fermion at $β=5.75$ on $12^3 \times 96$ with renormalized anisotropy $a_s/a_t=4$.For comparison, we first investigate the lowest $q\bar q$ scalar meson from the connected diagram and find its large mass of about 1.32GeV after chiral extrapolation, and thus the lowest $q\bar q$ scalar meson corresponds to $f_0(1370)$.We investigate the lowest 4Q state in the spatially periodic boundary condition, and find that it is just a two-pion scattering state, as is expected. To examine spatially-localized 4Q resonances, we use the Hybrid Boundary Condition (HBC) method, where anti-periodic and periodic boundary conditions are imposed on quarks and antiquarks, respectively. By applying HBC on a finite-volume lattice, the threshold of the two-meson scattering state is raised up, while the mass of a compact 4Q resonance is almost unchanged.In HBC, the lowest 4Q state appears slightly below the two-meson threshold. To clarify the nature of the 4Q system, we apply the Maximum Entropy Method (MEM) for the 4Q correlator and obtain the spectral function of the 4Q system.From the combination analysis of MEM with HBC, we finally conclude that the 4Q system appears as a two-pion scattering state and there is no spatially-localized 4Q resonance in the quark-mass region of $m_s< m_q <2m_s$.

hep-lat↗

arXiv2007

Five-quark picture of Lambda(1405) in anisotropic lattice QCD

Five-quark (5Q) picture of Lambda(1405) is studied using quenched lattice QCD with an exotic 5Q operator of N\bar{K} type. To discreminate mere N\bar{K} and Σπscattering states, Hybrid Boundary Condition (HBC), a flavor-dependent boundary condition, is imposed on the quark fields along spatial direction. 5Q mass m_{5Q}\simeq 1.89 GeV is obtained after the chiral extrapolation to the physical quark mass region, which is too heavy to be identified with Lambda(1405). Then, Lambda(1405) seems neither a pure 3Q state nor a pure 5Q state, and therefore we present an interesting possibility that Lambda(1405) is a mixed state of 3Q and 5Q states.

hep-lat↗

arXiv2005

Lattice QCD Evidence for Exotic Tetraquark Resonance

We study the manifestly exotic tetraquark D$_{\rm s0}^{++}(cu\bar s \bar d)$ and the scalar tetraquark $f_0(ud \bar u \bar d)$ in SU(3)$_c$ anisotropic quenched lattice QCD with the $O(a)$-improved Wilson (clover) fermion with various quark masses including the idealized SU(4)$_f$ case. For $f_0(ud\bar u \bar d)$ etc., we only consider connected diagrams at the quenched level, i.e., the tetraquark $f_0(ud\bar u\bar d)$ is identical with D$_{\rm s0}^{++} (cu\bar s \bar d)$ in the idealized SU(4)$_f$ case. First, for comparison, we study the lowest $q\bar q$ scalar meson, and find that it has a large mass of about 1.37GeV after chiral extrapolation, which corresponds to $f_0(1370)$. Second, we investigate the lowest 4Q state in the spatial periodic boundary condition, and find that it is just a scattering state of two pseudoscalar mesons, as is expected. Third, to extract spatially-localized 4Q resonances, we use the Hybrid Boundary Condition (HBC) method, where anti-periodic and periodic boundary conditions are imposed on quarks ($c$,$u$) and antiquarks ($\bar s$,$\bar d$), respectively. By applying the HBC on a finite-volume lattice, the threshold of the two-meson scattering state is raised up, while the mass of a compact 4Q resonance is almost unchanged. In HBC, we find a nontrivial 4Q resonance state about 100 MeV below the two-meson threshold in some quark-mass region. Its chiral behavior largely differs from a two-meson scattering state. The scalar tetraquark $f_0(ud\bar u\bar d)$ is found to have the mass of about 1.1GeV after chiral extrapolation, and seems to correspond to $f_0(980)$. Then, the manifestly exotic tetraquark D$_{\rm s0}^{++}(cu\bar s \bar d)$ would exist around 1GeV in the idealized SU(4)$_f$ chiral limit. Finally, MEM analysis is applied to obtain the spectral function of the 4Q system.

hep-lat↗

arXiv2005

Anisotropic lattice QCD study of pentaquark baryons in spin 3/2 channel

We perform the comprehensive analysis of the pentaquark (5Q) in J^P=3/2^{\pm} channel using anisotropic quenched lattice QCD. We employ the standard Wilson gauge action at β=5.75 and the O(a) improved Wilson (clover) quark action on a 12^3*96 lattice with the renormalized anisotropy as a_s/a_t = 4. A large number of gauge configurations as Nconf=1000 is analyzed, which is found to be essential to achieve a reliable measurement. We study three types of the Rarita-Schwinger intepolationg fields with I=0: (a) the NK*-type, (b) the (color-)twisted NK*-type, (c) a diquark-type. As a result, we find only massive states as m(5Q)= 2.1-2.2 GeV in J^P=3/2^- channel, and m(5Q) = 2.4-2.6 GeV in J^P=3/2^+ channel in the chiral limit. The analysis with the hybrid boundary condition (HBC) is performed to distinguish whether these resonances are compact 5Q resonances or two-particle scattering states. No low-lying compact 5Q resonance states are found below 2.1GeV.

hep-lat↗

arXiv2005

J/Ψat high temperatures in anisotropic lattice QCD

J/Ψand η_c above the QCD critical temperature T_c are studied in anisotropic quenched lattice QCD, considering whether the c\bar c systems above T_c are compact quasi-bound states or scattering states. We adopt the standard Wilson gauge action and O(a)-improved Wilson quark action with renormalized anisotropy a_s/a_t =4 at β=6.10 on 16^3\times (14-26) lattices, which correspond to the spatial lattice volume V\equiv L^3\simeq(1.55{\rm fm})^3 and temperatures T\simeq(1.11-2.07)T_c. To clarify whether compact charmonia survive in the deconfinement phase, we investigate spatial boundary-condition dependence of the energy of the c\bar c systems above T_c. In fact, for low-lying c \bar c scattering states, there appears a significant energy difference ΔE \equiv E{\rm (APBC)}-E{\rm (PBC)} between periodic and anti-periodic boundary conditions as ΔE\simeq2\sqrt{m_c^2+3π^2/L^2}-2m_c (m_c: charm quark mass) on the finite-volume lattice. In contrast, for compact charmonia, there is no significant energy difference between periodic and anti-periodic boundary conditions. As a lattice QCD result, we find almost no spatial boundary-condition dependence for the energy of the c\bar c system in J/Ψand η_c channels for T\simeq(1.11-2.07)T_c, which indicates that J/Ψand η_c would survive as compact c\bar c quasi-bound states below 2T_c.

hep-lat↗

arXiv2004

The lattice QCD simulation of the quark-gluon mixed condensate g<\bar{q} σG q> at finite temperature and the phase transition of QCD

The thermal effects on the quark-gluon mixed condensate g<\bar{q} σG q>, which is another chiral order parameter, are studied using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We perform the accurate measurement of the mixed condensate as well as the quark condensate for 0MeV<=T<=500MeV. We observe the sharp decrease of both the condensates around T_c \simeq 280MeV, while the thermal effects below T_c are found to be weak. We also find that the ratio m_0^2 = g<\bar{q} σG q>/<\bar{q}q> is almost independent of the temperature even in the very vicinity of T_c, which indicates that the two condensates have nontrivial similarity in the chiral behaviors. We also present the correlation between the condensates and the Polyakov loop to understand the vacuum structure of QCD.

hep-lat↗

arXiv2004

Thermal effects on quark-gluon mixed condensate g<\bar{q} σG q> from lattice QCD

We present the first study of the thermal effects on the quark-gluon mixed condensate g<\bar{q} σG q>, which is another chiral order parameter, in SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. Using the lattices at β=6.0, 6.1, 6.2 in high statistics, we calculate the mixed condensate as well as the quark condensate in the chiral limit for the temperature 0MeV <= T <= 500MeV. Except for the sharp decrease of both the condensates around T_c \simeq 280MeV, the thermal effects are found to be weak below T_c. We also find that the ratio m_0^2 = g<\bar{q} σG q>/ <\bar{q}q> is almost independent of the temperature even in the very vicinity of T_c. This result indicates nontrivial similarity in the chiral behaviors of the two different condensates.

hep-lat↗

arXiv2003

Properties of Thermal Glueballs

We study the properties of the 0++ glueball at finite temperature using SU(3) quenched lattice QCD. We find a significant thermal effects near T_c. We perform the χ^2 fit analyses adopting two Ansaetze for the spectral function, i.e., the conventional narrow-peak Ansatz and an advanced Breit-Wigner Ansatz. The latter is an extension of the former, taking account of the appearance of the thermal width at T>0. We also perform the MEM analysis. These analyses indicate that the thermal effect on the glueball is a significant thermal-width broadening Γ(T_c) \sim 300 MeV together with a modest reduction in the peak center Δω_0(T_c) \sim 100 MeV.

hep-lat↗

arXiv2003

The Study of Chiral Restoration using the Quark-Gluon Mixed Condensate g<\bar{q} σG q> in Lattice QCD at Finite Temperature

The quark-gluon mixed condensate g<\bar{q} σG q> is studied using SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. Using the lattices as β= 6.0 with 16^3 * N_t (N_t=16,12,10,8,6,4), β= 6.1 with 20^3 * N_t (N_t=20,12,10,8,6) and β= 6.2 with 24^3 * N_t (N_t=24,16,12,10,8) in high statistics of 100-1000 gauge configurations, we perform accurate measurement of the thermal effects on g<\bar{q} σG q> as well as <\bar{q}q> in the chiral limit. We find that the thermal effects on both the condensates are very weak except for the vicinity of T_c, while both the condensates suddenly vanish around T_c \simeq 280 MeV, which indicates strong chiral restoration near T_c. We also find that the ratio m_0^2 = g<\bar{q} σG q>/ <\bar{q}q> is almost independent of the temperature even in the very vicinity of T_c, which means that these two different condensates obey the same critical behavior. This nontrivial similarity between them would impose constraints on the chiral structure of the QCD vacuum near T_c.

hep-lat↗

arXiv2003

Thermal Effects on the Condensates of Chiral Order Parameters, the Quark Condensate and the Quark Gluon Mixed Condensate, and Chiral Restoration from Lattice QCD

We study the quark-gluon mixed condensate g<\bar{q} σG q> using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We perform the first but accurate measurement of the thermal effects on the mixed condensate in lattice QCD at β= 6.0 with 16^3 * Nt (Nt=16,12,10,8,6,4), β= 6.1 with 20^3 * Nt (Nt=20,12,10,8,6), and β= 6.2 with 24^3 * Nt (Nt=24,16,12,10,8). At each temperature, the lattice calculation is carried out with high statistics using more than 100 gauge configurations. In particular, about 1000 gauge configurations are used near the critical temperature T_c. The chiral extrapolation is done from the lattice result with the current-quark mass of m_q = 21,36,52 MeV. While the thermal effects on both of the mixed condensate and the quark condensate are very weak except for the vicinity of T_c, both the condensates suddenly vanish around T_c \simeq 280 MeV, which indicates strong chiral restoration near T_c. To compare the thermal effects on the two condensates, we analyze the ratio m_0^2 = g<\bar{q} σG q>/ <\bar{q}q>, and find that m_0^2 is almost independent of the temperature, even in the very vicinity of T_c. This means that these two different condensates obey the same critical behavior, and this nontrivial similarity between them would impose constraints on the chiral structure of the QCD vacuum near T_c.

hep-lat↗

arXiv2003

MEM Analysis of Glueball Correlators at T>0

Maximum Entropy Method (MEM) is applied to glueball correlators at finite temperature constructed by using 5,500-9,900 gauge field configurations generated in SU(3) quenched lattice QCD with the lattice parameter beta = 2N_c/g^2 = 6.25 and the renormalized anisotropy a_s/a_t = 4. The results support the thermal width broadening of the 0++ glueball near the critical temperature.

hep-lat↗

arXiv2003

A practical approach to the problem of the missing imaginary part of the handbag diagram in the confined Bethe-Salpeter framework

In the confined Bethe-Salpeter (BS) methods, the quark propagator is an entire function. Hence, the imaginary part of the handbag diagram disappears, leading to a problem of the vanishing parton distribution function (PDF). In contrast, the direct calculation of the light-cone (LC) momentum distribution does give a non-vanishing result even in the confined BS framework. We consider their precise relation and difference, and propose to use the latter as a practical approach to this problem. Our formalism is general enough to be applied to various effective models.

nucl-th↗

arXiv2003

Thermal Width Broadening of the 0++ Glueball Spectrum near Tc

We study the 0++ glueball correlator constructed with SU(3) anisotropic quenched lattice QCD at various temperature taking into account the possible existence of the thermal width in the ground-state peak. For this purpose, we adopt the Breit-Wigner ansatz, analysing the lattice data obtained with 5,500-9,900 gauge configurations at each T. The results indicate the significant thermal width broadening as Gamma(Tc) \sim 300 MeV with a reduction in the peak center as Delta omega_0(Tc) \sim 100 MeV in the vicinity of the critical temperature Tc.

hep-lat↗

arXiv2003

The Determination of the Quark-Gluon Mixed Condensate (anti-Q sigma G Q) from Lattice QCD

We study the quark-gluon mixed condensate g<\bar{q} sigma G q>, using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We generate 100 gauge configurations on the 16^4 lattice with β= 6.0, and perform the measurement of the mixed condensate at 16 points in each gauge configuration for each current quark mass of m_q=21, 36, 52 MeV. Using the 1600 data for each m_q, we find the ratio between the mixed condensate and the quark condensate, m_0^2 = g<\bar{q} sigma G q> / <\bar{q}q> \simeq 2.5 GeV^2 at the lattice scale of 1/a \simeq 2 GeV in the chiral limit. The large value of the mixed condensate suggests its importance in the operator product expansions in QCD. We study also chiral restoration at finite temperature in terms of the mixed condensate, which is another chiral order parameter. We present the lattice QCD results of the mixed condensate at finite temperature.

hep-lat↗

arXiv2003

The Quark-Gluon Mixed Condensate g<\bar{q} sigma G q> in SU(3)c Quenched Lattice QCD

Using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level, we study the quark-gluon mixed condensate g<\bar{q} sigma G q>, which is another chiral order parameter. For each current quark mass of m_q=21, 36, 52 MeV, we generate 100 gauge configurations in the 16^4 lattice with β= 6.0, and perform the measurement of the mixed condensate at 16 points in each gauge configuration. Using the 1600 data for each m_q, we find the ratio between the mixed condensate and the quark condensate, m_0^2 = g<\bar{q} sigma G q>/ <\bar{q}q> \simeq 2.5 GeV^2 at the lattice scale in the chiral limit. The large value of the mixed condensate suggests its importance in the operator product expansion in QCD.

hep-lat↗

arXiv2002

Lattice QCD study for the Quark-Gluon Mixed Condensate (anti-Q sigma G Q)

We study the quark-gluon mixed condensate g<\bar{q} sigma G q>, which is another chiral order parameter, using the SU(3)c lattice QCD with the Kogut-Susskind(KS) fermion at the quenched level. We generate 100 gauge configurations on the 16^4 lattice with β= 6.0, and measure the mixed condensate at 16 points in each gauge configuration for each current-quark mass of m_q=21, 36, 52 MeV. From the 1600 data for each m_q, we find the ratio between the mixed condensate and the quark condensate, m_0^2 = g<\bar{q} sigma G q> / <\bar{q}q> \simeq 2.5 GeV^2 at the lattice scale of 1/a \simeq 2 GeV in the chiral limit. The large value of the mixed condensate suggests its importance in the operator product expansions in QCD.

hep-lat↗

arXiv2002

The Thermal Glueball at Finite Temperature in SU(3) Anisotropic Lattice QCD

The thermal glueball is studied at finite temperature by using SU(3) anisotropic lattice QCD with beta_{lat}=6.25, the renormalized anisotropy xi = a_s/a_t = 4 over the lattice of the size 20^3xN_t with various N_t at the quenched level. While the narrow peak ansatz leads to the significant polemass reduction of about 300 MeV near the critical temperature T_c, Breit-Wigner ansatz which can take into account the possible appearance of the thermal width leads to the significant thermal width broadening of about 300 MeV with a modest reduction of the peak center of about 100 MeV.

hep-lat↗

arXiv2002

Quark-Gluon Mixed Condensate (anti-Q sigma G Q) from Lattice QCD

We study the quark-gluon mixed condensate g<\bar{q} sigma G q>, which is another chiral order parameter, in SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. Using 100 gauge configurations on the 16^4 lattice with β= 6.0, we measure the mixed condensate at 16 points in each gauge configuration for each current-quark mass of m_q=21, 36, 52 MeV. From the 1600 data for each m_q, we find the ratio between the mixed condensate and the quark condensate, m_0^2 = g<\bar{q} sigma G q> / <\bar{q}q> \simeq 2.5 GeV^2 at the lattice scale of 1/a \simeq 2 GeV in the chiral limit. The large value of the mixed condensate suggests its importance in the operator product expansions in QCD. We also show our preliminary results of the mixed condensate at finite temperature.

hep-lat↗