arXiv subjects

T. Onogi

Publications and source records attributed to T. Onogi.

119 records · Page 7Linked to original sources

arXiv1997

First study of $B \to π$ semileptonic decay form factors using NRQCD

We present a quenched calculation of the form factors of the semileptonic weak decay $B \to πl \barν$ with $O(1/m_Q)$ NRQCD heavy quark and Wilson light quark on a $16^3 \times 32$ lattice at $β=5.8$. The form factors are evaluated at six heavy quark masses, in the range of $m_Q \sim 1.5-8$ GeV. $1/m_Q$ dependence of matrix elements are investigated and compared with HQET predictions. We observe clear signal for the form factors near $q^2_{max}$, even at the $b$-quark mass range. $f^0(q^2_{max})$ is compared with $f_B/f_π$ based on the soft pion theorem and significant difference is observed.

hep-lat↗

arXiv1997

Heavy quark mass dependence of semileptonic form factors for B decays

We present our study of the dependence of the heavy-to-light semileptonic B decay form factors on the heavy-light meson mass $M_{PS}$. Simulations are made over a range of the heavy quark mass covering both the charm and bottom quarks using the $O(a)$-improved clover action at $β=5.9$ on a $16^3\times 40$ and $24^3\times 64$ lattice. We find that a weak dependence of form factors on $M_{PS}$ observed in previous studies in the region of charm quark persists up to the region of$b$ quark. The soft pion relation $f^0(q^2_{max})=f_B/f_π$ is examined and found to be largely violated.

hep-lat↗

arXiv1997

Perturbative renormalization parameters for heavy quarks

We study the heavy quark mass dependence of the perturbative renormalization factors for the heavy-light currents involving Wilson, Clover, and NRQCD heavy quarks. We find that the one-loop Z-factor for the axial-vector current depends significantly on the heavy quark mass commonly for all actions we study, while that for the vector current has smaller dependence.

hep-lat↗

arXiv1997

A study of $O(1/m_{Q}^{2})$ corrections for $f_{B}$ with lattice NRQCD

We investigate higher order effects in the nonrelativistic expansion of lattice QCD on the heavy-light meson decay constants and some other quantities in order to understand the truncation error of NRQCD. While our numerical results have large $O(a)$ and $O(α_s)$ errors due to the use of Wilson light quark action and the tree-level matching, we find that the truncation error of higher order relativistic corrections are adequately small around the mass of the $b$ quark. We also present a perturbatively matched results through 1-loop level without operator mixing effects.

hep-lat↗

arXiv1997

f_B with lattice NRQCD including O(1/m_Q^2) corrections

We calculate the heavy-light meson decay constant using lattice NRQCD action for the heavy quark and Wilson quark action for the light quark over a wide range in the heavy quark mass. Simulations are carried out on a 16^3 x 32 lattice with 120 quenched gauge configurations generated with the plaquette action at beta=5.8. For the heavy quark part of the calculation, two sets of lattice NRQCD action and current operator are employed. The first set includes terms up to O(1/m_Q) both in the action and the current operator, and the second set up to O(1/m_Q^2), where m_Q is the bare mass of the heavy quark. Tree-level values with tadpole improvement are employed for the coefficients in the expansion. We compare the results obtained from the two sets in detail and find that the truncation error of higher order relativistic corrections for the decay constant are adequately small around the mass of the b quark. We also calculate the 1S hyperfine splitting of B meson, M_{B_s} - M_B and f_{B_s}/f_B with both sets and find that the 1/m_Q^2 corrections are negligible. Remaining systematic errors and the limitation of NRQCD theory are discussed.

hep-lat↗

arXiv1996

Light Quark Masses with an O(a)-Improved Action

We present the recent Fermilab calculations of the masses of the light quarks, using tadpole-improved Sheikholeslami-Wohlert (SW) quarks. Various sources of systematic errors are studied. Our final result for the average light quark mass in the quenched approximation evaluated in the $\bar{MS}$ scheme is $\bar{m}_q(μ=2 GeV;n_f=0)= (m_u+m_d)/2=3.6 \pm 0.6 MeV$.

hep-lat↗

arXiv1995

Screening effect of interlayer coupling on electronic transport properties of layered high-$T_c$ oxides

We have investigated the effect of thermal fluctuation on the interlayer coupling of three-dimensional Josephson-junction arrays with anisotropic interactions as a model of layered high-$T_c$ oxides, focusing on non-Ohmic current-voltage characteristics. Langevin dynamic simulations were performed for various Josephson-coupling anisotropies and for various temperatures in both zero and finite magnetic fields. We find that, in the highly anisotropic region, the interlayer coupling, which causes the non-vanishing critical current ($I_{c}$), is suppressed by thermal fluctuations, and tends to push up the Kosterlitz-Thouless transition temperature ($T_{KT}$) of the two-dimensional (2D) regime. In this highly anisotropic region, $I_c$ begins to decrease drastically near $T_{KT}$. This suggests that interlayer coupling is screened by thermally excited 2D small vortex-antivortex pairs as well as the intralayer logarithmic part of vortex-antivortex interactions. Moreover, weak magnetic fields parallel to the $c$-axis affect only the logarithmic-interaction part between the 2D pancake vortices.

cond-mat↗

arXiv1994

Charmonium spectroscopy with heavy Kogut-Susskind quarks

Charmonium spectroscopy with Kogut-Susskind valence quarks are carried out for quenched QCD at $β=6.0$ and for two-flavor full QCD at $β=5.7$. Results for 1P--1S mass splitting and estimates of $α^{(5)}_{\overline{MS}}(m_Z)$ are reported. Problems associated with flavor breaking effects and finite size effects of $1P$ states are discussed.

hep-lat↗

arXiv1994

Manifestation of Sea Quark Effects in the Strong Coupling Constant in Lattice QCD

We demonstrate that sea quark effects of a magnitude expected from renormalization group considerations are clearly visible in the strong coupling constant measured in current full QCD simulations. Building on this result an estimate of $α_{\overline{MS}}^{(5)}(M_Z)$ is made employing the charmonium $1S-1P$ mass splitting calculated on full QCD configurations generated with two flavors of dynamical Kogut-Susskind quarks to fix the scale.

hep-lat↗

arXiv1994

Two-dimensional Superfluidity and Localization in the Hard-Core Boson Model: a Quantum Monte Carlo Study

Quantum Monte Carlo simulations are used to investigate the two-dimensional superfluid properties of the hard-core boson model, which show a strong dependence on particle density and disorder. We obtain further evidence that a half-filled clean system becomes superfluid via a finite temperature Kosterlitz-Thouless transition. The relationship between low temperature superfluid density and particle density is symmetric and appears parabolic about the half filling point. Disorder appears to break the superfluid phase up into two distinct localized states, depending on the particle density. We find that these results strongly correlate with the results of several experiments on high-$T_c$ superconductors.

cond-mat↗

arXiv1993

Sea Quark Effects on the Strong Coupling Constant

We present results showing that the strong coupling constant measured in two-flavor full QCD with dynamical Kogut-Susskind quarks at $β=5.7$ exhibit a 15\% increase due to sea quarks over that for quenched QCD at the scale $μ\approx 7$GeV . (talk at lattice93)

hep-lat↗