arXiv subjects

Takumi Doi

Publications and source records attributed to Takumi Doi.

105 records · Page 6Linked to original sources

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

Penta-quark baryon from the QCD Sum Rule

Exotic penta-quark baryon with strangeness +1, Θ^+, is studied in the QCD sum rule approach. We derive sum rules for the positive and negative parity baryon states with J=1/2 and I=0. It is found that the standard values of the QCD condensates predict a negative parity Θ^+ of mass \simeq 1.5 GeV, while no positive parity state is found. We stress the roles of chiral-odd condensates in determining the parity and mass of Θ^+.

hep-ph↗

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

Meson-Baryon Couplings from QCD Sum Rules

Coupling constants of the pseudoscalar mesons to the octet baryons are calculated in the QCD sum rule approach. Two-point correlation function of the baryons are evaluated in a single meson state and the vacuum, which yields the designated coupling. The emphasis is on the flavor SU(3) structure of the coupling constants and reliability in extracting the coupling constants from the two-point correlation functions. We first calculate the baryon-diagonal couplings and study the reliability of the sum rule. The F/D ratio of the coupling is determined in the SU(3) limit. We further formulate the baryon-off-diagonal couplings using the projected correlation functions and the vertex functions, so that the unwanted excited states do not contaminate the sum rule. As an example, the (π- Λ- Σ) coupling constant is calculated and the flavor SU(3) breaking effect is studied. We find that the effect of SU(3) breaking on the (π- Λ- Σ) coupling constant is small.

hep-ph↗

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

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 F/D Ratio and Meson-Baryon Couplings from QCD Sum Rules

Coupling constants of the pseudoscalar mesons to the octet baryons are computed in the QCD sum rule approach. The pi-NN, eta-NN, pi-XiXi, eta-XiXi, pi-SigmaSigma, eta-SigmaSigma as well as pi-Lambda-Sigma couplings are studied. Determining the pertinent Dirac structure in the correlation function, we analyze the couplings in the SU(3) limit. We find the F/D ratio to be \sim 0.6-0.8 that is consistent with the SU(6) value. We also estimate the SU(3) breaking effect using a projected correlation function method.

hep-ph↗

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↗

arXiv2000

Pertinent Dirac structure for QCD sum rules of meson-baryon coupling constants

Using general baryon interpolating fields $J_B$ for $B= N, Ξ, Σ, $ without derivative, we study QCD sum rules for meson-baryon couplings and their dependence on Dirac structures for the two-point correlation function with a meson $i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket$. Three distinct Dirac structures are compared: $iγ_5$, $iγ_5\fslash{p}$, and $γ_5σ_{μν}q^μp^ν$ structures. From the dependence of the OPE on general baryon interpolating fields, we propose criteria for choosing an appropriate Dirac structure for the coupling sum rules. The $γ_5σ_{μν}q^μp^ν$ sum rules satisfy the criteria while the $iγ_5$ sum rules beyond the chiral limit do not. For the $iγ_5\fslash{p}$ sum rules, the large continuum contributions prohibit reliable prediction for the couplings. Thus, the $γ_5σ_{μν}q^μp^ν$ structure seems pertinent for realistic predictions. In the SU(3) limit, we identify the OPE terms responsible for the $F/D$ ratio. We then study the dependence of the ratio on the baryon interpolating fields. We conclude the ratio $F/D \sim 0.6-0.8$ for appropriate choice of the interpolating fields.

nucl-th↗

arXiv2000

The $F/D$ ratio and meson-baryon couplings from QCD sum rules-II

Using QCD sum rules, we compute the diagonal meson-baryon couplings, $πNN$, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$, from the baryon-baryon correlation function with a meson, $i\int d^4x e^{iq\cdot x} < 0| T J_B(x) {\bar J}_B(0)|M(p)>$. The calculations are performed to leading order in $p_μ$ by considering the two separate Dirac structures, $i γ_5 γ_μp^μ$ and $γ_5 σ_{μν} {q^μp^ν}$ separately. We first improve the previous sum rule calculations on these Dirac structures for the $πNN$ coupling by including three-particle pion wave functions of twist 4 and then extend the formalism to calculate the other couplings, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$. In the SU(3) symmetric limit, we identify the terms responsible for the $F/D$ ratio in the OPE by matching the obtained couplings with their SU(3) relations. Depending on the Dirac structure considered, we find different identifications for the $F/D$ ratio. The couplings including the SU(3) breaking effects are also discussed within our approach.

nucl-th↗

arXiv1999

Meson-baryon couplings and the $F/D$ ratio from QCD sum rules

Motivated by the recent work on the calculation of the $πNN$ coupling constant using QCD sum rule beyond the chiral limit, we construct the corresponding sum rules for the couplings, $ηNN$, $πΞΞ$, $ηΞΞ$, $πΣΣ$ and $ηΣΣ$. In constructing the $η$-baryon sum rules, we use the second moment of the $η$ wave function, which we obtain from the pion wave function after SU(3) rotation. In the SU(3) symmetric limit, we can identify the term responsible for the $F/D$ ratio in the OPE, which after the sum rule analysis gives $F/D\sim 0.2$, a factor of 3 smaller than from other studies. We also present a qualitative analysis including the SU(3) breaking terms.

nucl-th↗