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Makoto Oka

Publications and source records attributed to Makoto Oka.

At least 127 records · Page 7Linked to original sources
arXiv2003

A quark model analysis of the charge symmetry breaking in nuclear force

In order to investigate the charge symmetry breaking (CSB) in the short range part of the nuclear force, we calculate the difference of the masses of the neutron and the proton, $Δ{\rm M}$, the difference of the scattering lengths of the p-p and n-n scatterings, $Δa$, and the difference of the analyzing power of the proton and the neutron in the n-p scattering, $ΔA(θ)$, by a quark model. In the present model the sources of CSB are the mass difference of the up and down quarks and the electromagnetic interaction. We investigate how much each of them contributes to $Δ{\rm M}$, $Δa$ and $ΔA(θ)$. It is found that the contribution of CSB of the short range part in the nuclear force is large enough to explain the observed $ΔA(θ)$, while $Δa$ is rather underestimated.

nucl-th↗
arXiv2003

U_A(1) Breaking Effects on the Light Scalar Meson Spectrum

Effects of the U_A(1) breaking interaction on the low-lying nonet scalar mesons are studied using the extended Nambu-Jona-Lasinio model. The strength of the U_A(1) breaking interaction is determined by the electromagnetic decays of the eta meson. We find that the U_A(1) breaking interaction gives rise to about 150 MeV mass difference between the sigma and a_0 mesons. We also find that the strangeness content in the σmeson is about 15%. The calculated mass of the I=1/2 state is about 200 MeV heavier than that of the I=1 state. The order of these masses is not likely to change within this model.

hep-ph↗
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

Proper construction of the continuum in light-cone QCD sum rules

A proper way of subtracting the continuum contributions in light-cone QCD sum rules (LCQSR) is demonstrated. Specifically, we calculate the continuum corresponding to a typical OPE appearing in LCQSR by properly combining the double dispersion relation with QCD duality. We demonstrate how the subtraction terms can spuriously contribute to the sum rules. In the limit of zero external momentum, taking out the spurious continuum is found to yield the sum rules using the single-variable dispersion relation. The continuum factor constructed in this way differs from the one appearing in usual LCQSR. The difference substantially affects the extraction of hadronic parameters from the correlation function involving baryon currents.

hep-ph↗
arXiv2003

Update on pion weak decay constants in nuclear matter

The QCD sum rule calculation of the in-medium pion decay constants using pseudoscalar-axial vector correlation function, $i \int d^4x e^{ip\cdot x} < ρ| T[{\bar d}(x) i γ_5 u (x) {\bar u}(0) γ_μγ_5 d (0)] | ρ>$ is revisited. In particular, we argue that the dimension 5 condensate, $<{\bar q} (i D_0)^2 q >_N + {1\over 8} < {\bar q} g_s σ\cdot {\cal G} q >_N$, which is crucial for splitting the time ($f_t$) and space ($f_s$) components of the decay constant, is not necessarily restricted to be positive. Its positive value is found to yield a tachyonic pion mass. Using the in-medium pion mass as an input, we fix the dimension 5 condensate to be around $-0.025 {\rm GeV}^2 \sim -0.019$ GeV$^2$. The role of the $N$ and $Δ$ intermediate states in the correlation function is also investigated. The $N$ intermediate state is found not to contribute to the sum rules. For the $Δ$ intermediate state, we either treat it as a part of the continuum or propose a way to subtract explicitly from the sum rules. With (and without) explicit $Δ$ subtraction while allowing the in-medium pion mass to vary within 139 MeV $ \le m_π^* \le$ 159 MeV, we obtain $f_s/f_π= 0.37 \sim 0.78$ and $f_t / f_π= 0.63 \sim 0.79$.

hep-ph↗
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↗
arXiv2001

Chiral Symmetry of Baryons

We study chiral symmetry aspects of the positive and negative parity baryons by identifying them with linear representations of the chiral group $SU(N_{f}) \otimes SU(N_{f})$. It is shown that there are two distinctive schemes: naive and mirror assignments. We construct linear sigma models for baryons in the two assignments and examine their physical implications. Then we investigate properties of the naive and mirror nucleons microscopically by using QCD interpolating fields. Finally, we propose experiments to distinguish the two chiral assignments for the nucleon.

hep-ph↗
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

Effects of Instantons on the YN Interaction

We investigate the symmetric and anti-symmetric spin-orbit forces (SLS and ALS) of the effective $Λ$N interaction derived from a quark cluster model with the instanton-induced interaction (\III), which can reproduce the observed YN cross sections as well as the observed NN scattering data. It is found that coupling to the $Σ$N channel enhances $Λ$N ALS, and therefore that the cancellation between SLS and ALS in the $Λ$N channel becomes more complete. This may be one of the major reasons why the single-particle spin-orbit force of $Λ$ in nuclei is weak.

hep-ph↗
arXiv2000

Probing chiral symmetry of nucleon by threshold $ηπ$ production

Double meson production of the eta and pion at the threshold region is investigated in order to determine chiral property of the nucleon. The eta can be used as a probe for the negative parity nucleon $N^* \equiv N^*(1535)$ produced in the intermediate state. The coupling of the low energy pion in the final state is then used to extract the sign of the Yukawa coupling, $\gpRR$, which distinguishes the two realizations of chiral symmetry, either naive or mirror, for the nucleon.

hep-ph↗
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↗
arXiv1999

Chiral Symmetry and Weak Decay of Hypernuclei

The weak decays of hyperons and hypernuclei are studied from the chiral symmetry viewpoint. The soft pion relations are useful in understanding the isospin properties of the weak hyperon decays. Recent development on the short-range part of the $\Lam N\to NN$ weak transitions shows fairly good account of the weak decays of hypernuclei, though it fails to explain the $n/p$ ratio. The $\pip$ decays of light hypernuclei are studied in the soft pion approach. They are related to the $\DI=3/2$ amplitudes of the nonmesonic decay.

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