arXiv subjects

Y. Namekawa

Publications and source records attributed to Y. Namekawa.

At least 19 recordsLinked to original sources

arXiv2019

Finite size effect on vector meson and baryon sectors in 2+1 flavor QCD at the physical point

We investigate the finite size effect on the vector meson and the baryon sectors using a subset of the "PACS10" configurations which are generated, keeping the space-time volumes over (10 fm$)^4$ in 2+1 flavor QCD at the physical point. Comparing the results on (5.5 fm$)^4$ and (10.9 fm$)^4$ lattices the ground states of octet baryons , which are stable on the lattice, show no finite size effect within less than 0.5% level of statistical errors. For those of vector mesons, which are unstable on the lattice, we observe that the effective masses are well below the experimental resonance levels both on (5.5 fm$)^4$ and (10.9 fm$)^4$ lattices. For the decuplet baryon sector we have found that the time dependence of the effective mass looks quite similar to that for the vector meson sector including the $Ω$ baryon channel. We discuss its origin due to a possible mixing with the nearby multihadron states. Since the $Ξ$ baryon mass can be determined with the smallest ambiguity among the vector meson and the baryon masses, we use it together with the pion and kaon masses as the physical inputs to determine the physical point.

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arXiv2019

Finite size effect on pseudoscalar meson sector in 2+1 flavor QCD at the physical point

We investigate the finite size effect on pseudoscalar meson masses and decay constants using a subset of the "PACS10" configurations which are generated keeping the space-time volumes over (10 fm$)^4$ in 2+1 flavor QCD at the physical point. We have tried two kinds of analyses, fixing $κ$ values or measured axial Ward identity quark masses. Comparing the results on (5.4 fm$)^4$ and (10.8 fm$)^4$ lattices, we have found a sizable finite size effect on the pseudoscalar meson sector in the former analysis: a 2.1(8)%, 4.8(1.6)%, and 0.36(31)% finite size effect on $m_π$, $m_{\rm ud}$, and $f_π$, respectively, on the (5.4 fm$)^4$ lattice. For the latter analysis, the finite size effect on the pseudoscalar meson decay constants is 0.66(33)% for $f_π$, 0.26(13)% for $f_K$, and 0.40(32)% for $f_K/f_π$. These values with two-sigma error bars are consistent with the predictions from the full one-loop SU(3) chiral perturbation theory, which are 0.20% for $f_π$, 0.08% for $f_K$, and 0.13% for $f_K/f_π$. The finite size effect on the pseudoscalar meson masses is hardly detected under the current statistical precision.

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arXiv2018

Scattering length from BS wave function inside the interaction range

We evaluate $I=2$ two-pion scattering length through the scattering amplitude obtained by the Bethe-Salpeter wave function inside the interaction range. The scattering length is computed with $m_π= 0.52-0.86$ GeV in the quenched lattice QCD. Furthermore, the half-off-shell amplitude is calculated, from which the effective range is extracted. Our results are compared with those by the conventional finite size method and by chiral perturbation theory to confirm consistency.

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arXiv2015

2+1 flavor QCD simulation on a $96^4$ lattice

We generate $2+1$ flavor QCD configurations near the physical point on a $96^4$ lattice employing the 6-APE stout smeared Wilson clover action with a nonperturbative $c_{\rm SW}$ and the Iwasaki gauge action at $β=1.82$. The physical point is estimated based on the chiral perturbation theory using several data points generated by the reweighting technique from the simulation point, wherer $m_π$,$m_K$ and $m_Ω$ are used as physical inputs. The physics results include the quark masses, the hadron spectrum, the pseudoscalar meson decay constants and nucleon sigma terms, using the nonperturbative renormalization factors evaluated with the Schrodinger functional method.

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arXiv2015

Mass and Axial current renormalization in the Schrödinger functional scheme for the RG-improved gauge and the stout smeared $O(a)$-improved Wilson quark actions

We present the quark mass and axial current renormalization factors for the RG-improved Iwasaki gauge action and three flavors of the stout smeared $O(a)$-improved Wilson quark action. We employ $α=0.1$ and $n_{\mathrm{step}}=6$ for the stout link smearing parameters and all links in the quark action are replaced with the smeared links. Using the Schrödinger functional scheme we evaluate the renormalization factors at $β=1.82$ where large scale simulations are being carried out.

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arXiv2013

Charmed baryons at the physical point in 2+1 flavor lattice QCD

We investigate the charmed baryon mass spectrum using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are tuned to their physical values, reweighted from those employed in the configuration generation. At the physical point, the inverse lattice spacing determined from the $Ω$ baryon mass gives $a^{-1}=2.194(10)$ GeV, and thus the spatial extent becomes $L = 32 a = 2.88(1)$ fm. Our results for the charmed baryon masses are consistent with experimental values, except for the mass of $Ξ_{cc}$, which has been measured by only one experimental group so far and has not been confirmed yet by others. In addition, we report values of other doubly and triply charmed baryon masses, which have never been measured experimentally.

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arXiv2012

Charmed baryon spectroscopy on the physical point in 2+1 flavor lattice QCD

We investigate the charmed baryon mass spectrum using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. At the physical point, the lattice spacing equals $a^{-1}=2.194(10)$ GeV and the spatial extent $L=2.88(1)$ fm. Our results for the charmed baryon masses are consistent with experiments except for $Ξ_{cc}$, which has only weak experimental evidence yet. We also predict mass values for other doubly and triply charmed baryons.

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arXiv2012

1+1+1 flavor QCD + QED simulation at the physical point

We present the results of 1+1+1 flavor QCD+QED simulation at the physical point, in which the dynamical quark effects in QED and the up-down quark mass difference are incorporated by the reweighting technique. The physical quark masses together with the lattice spacing are determined with $m_{π^+}$, $m_{K^+}$, $m_{K^0}$ and $m_{Ω^-}$ as physical inputs. Calculations are carried out using a set of 2+1 flavor QCD configurations near the physical point generated by the non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action at $β=1.9$ on a $32^3\times 64$ lattice. We evaluate the values of the up, down and strange quark masses individually with non-perturbative QCD renormalization.

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arXiv2011

$ρ$ Meson Decay in 2+1 Flavor Lattice QCD

We perform a lattice QCD study of the $ρ$ meson decay from the $N_f=2+1$ full QCD configurations generated with a renormalization group improved gauge action and a non-perturbatively $O(a)$-improved Wilson fermion action. The resonance parameters, the effective $ρ\toππ$ coupling constant and the resonance mass, are estimated from the $P$-wave scattering phase shift for the isospin I=1 two-pion system. The finite size formulas are employed to calculate the phase shift from the energy on the lattice. Our calculations are carried out at two quark masses, $m_π=410\,{\rm MeV}$ ($m_π/m_ρ=0.46$) and $m_π=300\,{\rm MeV}$ ($m_π/m_ρ=0.35$), on a $32^3\times 64$ ($La=2.9\,{\rm fm}$) lattice at the lattice spacing $a=0.091\,{\rm fm}$. We compare our results at these two quark masses with those given in the previous works using $N_f=2$ full QCD configurations and the experiment.

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arXiv2011

Charm quark system on the physical point in 2+1 flavor lattice QCD

We investigate the charm quark system on 2+1 flavor PACS-CS configurations. Calculations are performed at the lattice spacing $a^{-1}=2.194(10)$ GeV and the spatial extent $L=2.9$ fm with O(a)-improved Wilson fermions for the light quarks and the relativistic heavy fermion for the charm quark. Our dynamical $ud$ and strange quark masses and valence charm quark mass are set to their physical values. A comparison of the mass spectrum and decay constants with experiments is presented. Our results for the charm quark mass and CKM matrix elements are also reported.

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arXiv2011

Charm quark system at the physical point of 2+1 flavor lattice QCD

We investigate the charm quark system using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. At the physical point, the lattice spacing equals $a^{-1}=2.194(10)$ GeV and the spatial extent $L=2.88(1)$ fm. The charm quark mass is determined by the spin-averaged mass of the 1S charmonium state, from which we obtain $m_{\rm charm}^{\msbar}(μ= m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35)$ GeV, where the errors are due to our statistics, scale determination and renormalization factor. An additional systematic error from the heavy quark is of order $α_s^2 f(m_Q a)(a Λ_{QCD})$, which is estimated to be a percent level if the factor $f(m_Q a)$ analytic in $m_Q a$ is of order unity. Our results for the charmed and charmed-strange meson decay constants are $f_D=226(6)(1)(5)$ MeV, $f_{D_s}=257(2)(1)(5)$ MeV, again up to the heavy quark errors of order $α_s^2 f(m_Q a)(a Λ_{QCD})$. Combined with the CLEO values for the leptonic decay widths, these values yield $|V_{cd}| = 0.205(6)(1)(5)(9)$, $|V_{cs}| = 1.00(1)(1)(3)(3)$, where the last error is on account of the experimental uncertainty of the decay widths.

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arXiv2010

Calculation of $ρ$ meson decay width from the PACS-CS configurations

We present preliminary results on the $ρ$ meson decay width from $N_f=2+1$ full QCD configurations generated by PACS-CS Collaboration. The decay width is estimated from the $P$-wave scattering phase shift for the isospin $I=1$ two-pion system. The finite size formula presented by Lüscher in the center of mass frame and its extension to non-zero total momentum frame by Rummukainen and Gottlieb are employed for the calculations of the phase shift. Our calculations are carried out at $m_π=410\ {\rm MeV}$ ($m_π/m_ρ=0.46$) and $a=0.091\ {\rm fm}$ on a $32^3\times 64$ ($La=2.9 {\rm fm}$) lattice.

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arXiv2010

Non-perturbative renormalization of quark mass in Nf=2+1 QCD with the Schroedinger functional scheme

We present an evaluation of the quark mass renormalization factor for Nf=2+1 QCD. The Schroedinger functional scheme is employed as the intermediate scheme to carry out non-perturbative running from the low energy region, where renormalization of bare mass is performed on the lattice, to deep in the high energy perturbative region, where the conversion to the renormalization group invariant mass or the MS-bar scheme is safely carried out. For numerical simulations we adopted the Iwasaki gauge action and non-perturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy regions and three lattice spacings to take the continuum limit at each scale. The regularization independent step scaling function of the quark mass for the Nf=2+1 QCD is obtained in the continuum limit. Renormalization factors for the pseudo scalar density and the axial vector current are also evaluated for the same action and the bare couplings as two recent large scale Nf=2+1 simulations; previous work of the CP-PACS/JLQCD collaboration, which covered the up-down quark mass range heavier than $m_π\sim 500$ MeV and that of PACS-CS collaboration for much lighter quark masses down to $m_π=155$ MeV. The quark mass renormalization factor is used to renormalize bare PCAC masses in these simulations.

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arXiv2010

Physical Point Simulation in 2+1 Flavor Lattice QCD

We present the results of the physical point simulation in 2+1 flavor lattice QCD with the nonperturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action at $β=1.9$ on a $32^3 \times 64$ lattice. The physical quark masses together with the lattice spacing is determined with $m_π$, $m_K$ and $m_Ω$ as physical inputs. There are two key algorithmic ingredients to make possible the direct simulation at the physical point: One is the mass-preconditioned domain-decomposed HMC algorithm to reduce the computational cost. The other is the reweighting technique to adjust the hopping parameters exactly to the physical point. The physics results include the hadron spectrum, the quark masses and the pseudoscalar meson decay constants. The renormalization factors are nonperturbatively evaluated with the Schr{ö}dinger functional method. The results are compared with the previous ones obtained by the chiral extrapolation method.

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arXiv2009

Heavy-light mesons in 2+1 flavor lattice QCD

Heavy-light meson system is investigated using the relativistic heavy quark action on the 2+1 dynamical flavor PACS-CS configurations at the lattice spacing $a^{-1}=2.2$ GeV and the spatial extent L=3 fm. Dynamical up-down and strange quark masses as well as the valence charm quark mass are set around their physical values. We measure the charm-$ud$ and charm-strange meson masses and decay constants. Our results are consistent with the experimental values except the hyperfine splitting of the charm-strange meson. We also estimate the CKM matrix elements in the second row.

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arXiv2009

Precise determination of the strong coupling constant in Nf=2+1 lattice QCD with the Schrödinger functional scheme

We present an evaluation of the running coupling constant for Nf=2+1 QCD. The Schroedinger functional scheme is used as the intermediate scheme to carry out non-perturbative running from the low energy region, where physical scale is introduced, to deep in the high energy perturbative region, where conversion to the MS-bar scheme is safely performed. Possible systematic errors due to the use of perturbation theory occur only in the conversion from three-flavor to four-flavor running coupling constant near the charm mass threshold, where higher order terms beyond 5th order in the $β$ function may not be negligible. For numerical simulations we adopted Iwasaki gauge action and non-perturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy region and three lattice spacings to take the continuum limit at each scale. A physical scale is introduced from the previous Nf=2+1 simulation of the CP-PACS/JL-QCD collaboration, which covered the up-down quark mass range heavier than $m_π\sim 500$ MeV.

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arXiv2009

SU(2) and SU(3) chiral perturbation theory analyses on baryon masses in 2+1 flavor lattice QCD

We investigate the quark mass dependence of baryon masses in 2+1 flavor lattice QCD using SU(3) heavy baryon chiral perturbation theory up to one-loop order. The baryon mass data used for the analyses are obtained for the degenerate up-down quark mass of 3 MeV to 24 MeV and two choices of the strange quark mass around the physical value. We find that the SU(3) chiral expansion fails to describe both the octet and the decuplet baryon data if phenomenological values are employed for the meson-baryon couplings. The SU(2) case is also examined for the nucleon. We observe that higher order terms are controlled only around the physical point. We also evaluate finite size effects using SU(3) heavy baryon chiralperturbation theory, finding small values of order 1% even at the physical point.

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arXiv2008

Charm quark system in 2+1 flavor lattice QCD using the PACS-CS configurations

We study heavy-heavy and heavy-light quark systems for charm with a relativistic heavy quark action in 2+1 flavor lattice QCD. Configurations are generated by the PACS-CS Collaboration at the lattice spacing is $a=0.09$ fm with the lattice size of $32^3\times 64$ employing the $O(a)$-improved Wilson quark action and the Iwasaki gauge action. We present preliminary results for the charmonium spectrum and the $D$ and $D_s$ meson decay constants evaluated at 3.5 MeV$< m_{\rm ud}<$ 12 MeV with $m_{\rm s}$ around the physical value. We investigate the dynamical quark mass dependences of the hyperfine and the orbital splittings. The decay constants are compared with the recent experimental values.

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