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Tetsuya Onogi

Publications and source records attributed to Tetsuya Onogi.

88 records · Page 5Linked to original sources
arXiv2004

Heavy Quarks on the Lattice

Lattice quantum chromodynamics provides first principles calculations for hadrons containing heavy quarks -- charm and bottom quarks. Their mass spectra, decay rates, and some hadronic matrix elements can be calculated on the lattice in a model independent manner. In this review, we introduce the effective theories that treat heavy quarks on the lattice. We summarize results on the heavy quarkonium spectrum, which verify the validity of the effective theory approach. We then discuss applications to $B$ physics, which is the main target of the lattice theory of heavy quarks. We review progress in lattice calculations of the $B$ meson decay constant, the $B$ parameter, semi-leptonic decay form factors, and other important quantities.)

hep-ph↗
arXiv2004

Theta vacuum effects on the chiral condensation and the eta^prime meson correlators in the two-flavor massive QED_2 on the lattice

We study the scalar and pseudoscalar condensations and the eta^prime meson correlators of the two-flavor massive Schwinger model in the non-zero theta vacuum. Exploiting our new method which was developed to investigate topological effects in the previous work, we find that the pseudoscalar condensation is non-zero and there exists a long-range correlation of the eta^prime meson. This phenomenon is well described by the clustering property. We also find that even in theta=0 case the cancellation of the long-range correlation is nontrivial and requires accurate contributions from higher topological sectors. Our results imply that the fluctuation of the ``disconnected'' diagram originates from the pseudoscalar condensation in each topological sector.

hep-lat↗
arXiv2003

Anisotropic lattices for precision computations in heavy flavor physics

We study the anisotropic lattice QCD for precision computations of heavy-light matrix elements. Our previous study in which the lattices are calibrated with a few percent accuracy has already given results comparable to the existing calculations. This suggests that even higher precision may be achieved by a more precise calibration of anisotropic lattices. We describe our strategy to tune the gauge and quark parameters with accuracies much less than 1 % in the quenched approximation.

hep-lat↗
arXiv2003

Lattice Study of the Massive Schwinger Model with a $θ$ term under Lüscher's "Admissibility" condition

We present a numerical study of the massive two-flavor QED in two dimensions with the gauge action proposed by Lüscher, which allows only ``admissible'' gauge fields. We find that the admissibility condition does not allow any topology changes by the local updation in Hybrid Monte Carlo algorithm so that the configurations in each topological sector can be generated separately. By developing a new method to sum over different topological sectors, we investigate $θ$ vacuum effects. Combining with domain-wall fermion action, we obtain the fermion mass dependence and $θ$ dependence of the meson masses, which are consistent with the analytic results by mass perturbation in the continuum theory.

hep-lat↗
arXiv2003

Lattice Study of the Massive Schwinger Model with $θ$ Term under Lüscher's "Admissibility" Condition

Lüscher's ``admissibility'' condition on the gauge field space plays an essential role in constructing lattice gauge theories which has exact chiral symmetries. We apply the gauge action proposed by Lüscher with the domain-wall fermion action to the numerical simulation of the massive Schwinger model. We find this action can generate configurations in each topological sector separately without any topology changes. By developing a new method to sum over different topological sectors, we calculate meson masses in nonzero-$θ$ vacuum.

hep-lat↗
arXiv2002

Perturbative calculation of O(a) improvement coefficients

We compute several coefficients needed for O(a) improvement of currents in perturbation theory, using the Brodsky-Lepage-Mackenzie prescription for choosing an optimal scale q*. We then compare the results to non-perturbative calculations. Normalization factors of the vector and axial vector currents show good agreement, especially when allowing for small two-loop effects. On the other hand, there are large discrepancies in the coefficients of O(a) improvement terms. We suspect that they arise primarily from power corrections inherent in the non-perturbative methods.

hep-lat↗
arXiv2002

Heavy quark action on the anisotropic lattice

We investigate the $O(a)$ improved quark action on anisotropic lattice as a potential framework for the heavy quark, which may enable precision computation of hadronic matrix elements of heavy-light mesons. The relativity relations of heavy-light mesons as well as of heavy quarkonium are examined on a quenched lattice with spatial lattice cutoff $a_σ^{-1} \simeq$ 1.6 GeV and the anisotropy $ξ=4$. We find that the bare anisotropy parameter tuned for the massless quark describes both the heavy-heavy and heavy-light mesons within 2% accuracy for the quark mass $a_σm_Q < 0.8$, which covers the charm quark mass. This bare anisotropy parameter also successfully describes the heavy-light mesons in the quark mass region $a_σm_Q \leq 1.2$ within the same accuracy. Beyond this region, the discretization effects seem to grow gradually. The anisotropic lattice is expected to extend by a factor $ξ$ the quark mass region in which the parameters in the action tuned for the massless limit are applicable for heavy-light systems with well controlled systematic errors.

hep-lat↗
arXiv2001

Application of heavy-quark effective theory to lattice QCD: III. Radiative corrections to heavy-heavy currents

We apply heavy-quark effective theory (HQET) to separate long- and short-distance effects of heavy quarks in lattice gauge theory. In this paper we focus on flavor-changing currents that mediate transitions from one heavy flavor to another. We stress differences in the formalism for heavy-light currents, which are discussed in a companion paper, showing how HQET provides a systematic matching procedure. We obtain one-loop results for the matching factors of lattice currents, needed for heavy-quark phenomenology, such as the calculation of zero-recoil form factors for the semileptonic decays $B\to D^{(*)}lν$. Results for the Brodsky-Lepage-Mackenzie scale $q^*$ are also given.

hep-lat↗
arXiv2001

Numerical study of O(a) improved Wilson quark action on anisotropic lattice

The $O(a)$ improved Wilson quark action on the anisotropic lattice is investigated. We carry out numerical simulations in the quenched approximation at three values of lattice spacing ($a_σ^{-1}=1$--2 GeV) with the anisotropy $ξ=a_σ/a_τ=4$, where $a_σ$ and $a_τ$ are the spatial and the temporal lattice spacings, respectively. The bare anisotropy $γ_F$ in the quark field action is numerically tuned by the dispersion relation of mesons so that the renormalized fermionic anisotropy coincides with that of gauge field. This calibration of bare anisotropy is performed to the level of 1 % statistical accuracy in the quark mass region below the charm quark mass. The systematic uncertainty in the calibration is estimated by comparing the results from different types of dispersion relations, which results in 3 % on our coarsest lattice and tends to vanish in the continuum limit. In the chiral limit, there is an additional systematic uncertainty of 1 % from the chiral extrapolation. Taking the central value $γ_F=γ_F^*$ from the result of the calibration, we compute the light hadron spectrum. Our hadron spectrum is consistent with the result by UKQCD Collaboration on the isotropic lattice. We also study the response of the hadron spectrum to the change of anisotropic parameter, $γ_F \to γ_F^* + δγ_F$. We find that the change of $γ_F$ by 2 % induces a change of 1 % in the spectrum for physical quark masses. Thus the systematic uncertainty on the anisotropic lattice, as well as the statistical one, is under control.

hep-lat↗
arXiv2001

O(a)-improved quark action on anisotropic lattices and perturbative renormalization of heavy-light currents

We investigate the Symanzik improvement of the Wilson quark action on anisotropic lattices. Taking first a general action with nearest-neighbor and clover interactions, we study the mass dependence of the ratio of the hopping parameters, the clover coefficients, and an improvement coefficient for heavy-light vector and axial vector currents. We show how tree-level improvement can be achieved. For a particular choice of the spatial Wilson coupling, the results simplify, and $O(m_0a_τ)$ improvement is possible. (Here $m_0$ is the bare quark mass and $a_τ$ the temporal lattice spacing.) With this choice we calculate the renormalization factors of heavy-light bilinear operators at one-loop order of perturbation theory employing the standard plaquette gauge action.

hep-lat↗
arXiv1997

NRQCD Results on Form Factors

We report results on $f_B$ and semi-leptonic $B$ decay form factors using NRQCD. We investigate $1/M$ scaling behavior of decay amplitudes. For $f_B$ Effect of higher order relativistic correction terms are also studied.

hep-lat↗
arXiv1997

Predictions of $m_b/m_τ$ and $m_t$ in an Asymptotically Non-Free Theory

We discuss an extention of the Minimal Supersymmetric Standard Model (MSSM) with the 4th and anti-4th generations which have $SU(2)_L\times U(1)_Y$ invariant masses. Due to the the extra generations, all three running gauge couplings become asymptotically non--free while preserving gauge coupling unification at the GUT scale. We show that due to the asymptotically non--free character of the gauge couplings: (1) the top and bottom Yukawa couplings are strongly focused onto infrared fixed points as they are evolved down in scale making their values at $μ=\mz$ insensitive to their initial values at $μ=\mgut$; (2) the model predicts $\R(\mz) \equiv Y_b/Y_τ|_{μ=\mz}\approx 1.8$, which is consistent with the experimental value provided we take the ratio of Yukawa couplings at the GUT scale to be $\R(\mgut) = Y_b/Y_τ|_{μ= \mgut} = 1/3$; (3) the $t$ mass prediction comes out to be $\mt\approx 180\,\GeV$ which is also consistent with experiment.

hep-ph↗
arXiv1996

The Light Quark Masses from Lattice Gauge Theory

We investigate the masses of the light quarks with lattice QCD. We show that most of the large dependence on the lattice spacing, a, observed in previous determinations using Wilson fermions is removed with the use of an O(a) corrected action. In the quenched approximation, we obtain for the strange quark MS bar mass m_s(2 GeV) = 95 (16) MeV, and for the average of the up and down quark masses m_l(2 GeV) = 3.6 (6) MeV. Short distance arguments and existing staggered fermion calculations make it likely that the answers including the effects of quark loops lie 20 % to 40 % below this: m_s(2 GeV) in the range 54-92 MeV, and m_l(2 GeV) in the range 2.1-3.5 MeV. We argue that almost all lattice determinations of the light quark masses are consistent with these values. These low values are outside the range usually given by conventional phenomenology.

hep-ph↗
arXiv1995

Effects of Improvement: $f_π$ and $m_q$

We present a study of the effects of improvement on light-quark physics using the Fermilab formalism. The calculations were performed at three different lattice spacings, with the SW action and traditional Wilson action (both tadpole improved). We find that $O(a)$ effects for the decay constant $f_π$ and quark mass $m_q$ can be successfully removed using the tadpole-improved SW action in the light-quark regime.

hep-lat↗
arXiv1992

Spontaneously Broken Technicolor and the Dynamics of Virtual Vector Technimesons

We propose spontaneously breaking technicolor, thus liberating techniquarks and suppressing large resonance contributions to the electroweak $S$ parameter. The dynamics is modeled by a fermion bubble approximation to a single massive techni--gluon exchange potential. This contains a Nambu--Jona-Lasinio model with additional interactions. ``Virtual'' vector mesons occur and contribute to $S$, and their effects are studied. Models of broken technicolor are discussed.

hep-ph↗