arXiv subjects

T. Kawanai

Publications and source records attributed to T. Kawanai.

6 recordsLinked to original sources

arXiv2018

Hadronic vacuum polarization contribution to the anomalous magnetic moments of leptons from first principles

We compute the leading, strong-interaction contribution to the anomalous magnetic moment of the electron, muon and tau using lattice quantum chromodynamics (QCD) simulations. Calculations include the effects of $u$, $d$, $s$ and $c$ quarks and are performed directly at the physical values of the quark masses and in volumes of linear extent larger than $6\,\mathrm{fm}$. All connected and disconnected Wick contractions are calculated. Continuum limits are carried out using six lattice spacings. We obtain $a_e^\mathrm{LO-HVP}=189.3(2.6)(5.6)\times 10^{-14}$, $a_μ^\mathrm{LO-HVP}=711.1(7.5)(17.4)\times 10^{-10}$ and $a_τ^\mathrm{LO-HVP}=341.0(0.8)(3.2)\times 10^{-8}$, where the first error is statistical and the second is systematic.

hep-lat↗

arXiv2016

Slope and curvature of the hadron vacuum polarization at vanishing virtuality from lattice QCD

We compute the slope and curvature, at vanishing four-momentum transfer squared, of the leading order hadron vacuum polarization function, using lattice QCD. Calculations are performed with 2+1+1 flavors of staggered fermions directly at the physical values of the quark masses and in volumes of linear extent larger than 6fm. The continuum limit is carried out using six different lattice spacings. All connected and disconnected contributions are calculated, up to and including those of the charm.

hep-lat↗

arXiv2016

Lattice QCD for Cosmology

We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.

hep-lat↗

arXiv2016

The B*Bpi coupling using relativistic heavy quarks

We report on a calculation of the B*Bpi coupling in lattice QCD. The strong matrix element for a B* to Bpi transition is directly related to the leading order low-energy constant in heavy meson chiral perturbation theory (HMChPT) for B mesons. We carry out our calculation directly at the b-quark mass using a non-perturbatively tuned clover action that controls discretization effects of order pa and (ma)^n for all n. Our analysis is performed on RBC/UKQCD gauge configurations using domain-wall fermions and the Iwasaki gauge action at two lattice spacings of ainverse = 1.729(25) GeV, ainverse = 2.281(28) GeV, and unitary pion masses down to 290 MeV. We achieve good statistical precision and control all systematic uncertainties, giving a final result for the HMChPT coupling g_b = 0.56(3)stat(7)sys in the continuum and at the physical light-quark masses. This is the first calculation performed directly at the physical b-quark mass and lies in the region one would expect from carrying out an interpolation between previous results at the charm mass and at the static point.

hep-lat↗

arXiv2015

$B \to π\ell ν$ and $B_s \to K \ell ν$ form factors and $|V_{ub}|$ from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

We calculate the $B \toπ\ellν$ and $B_s \to K \ellν$ form factors in dynamical lattice QCD. We use the (2+1)-flavor RBC-UKQCD gauge-field ensembles generated with the domain-wall fermion and Iwasaki gauge actions. For the $b$ quarks we use the anisotropic clover action with a relativistic heavy-quark interpretation. We analyze two lattice spacings $a \approx 0.11, 0.086$ fm and unitary pion masses as light as $M_π\approx 290$ MeV. We simultaneously extrapolate our numerical results to the physical light-quark masses and to the continuum and interpolate in the pion/kaon energy using SU(2) "hard-pion" chiral perturbation theory. We provide complete error budgets for the form factors $f_+(q^2)$ and $f_0(q^2)$ at three momenta that span the $q^2$ range accessible in our numerical simulations. We extrapolate these results to $q^2 = 0$ using a model-independent $z$-parametrization and present our final form factors as the $z$-coefficients and the matrix of correlations between them. Our results agree with other lattice determinations using staggered light quarks and provide important independent cross-checks. Both $B \toπ\ellν$ and $B_s \to K \ellν$ decays enable a determination of the CKM matrix element $|V_{ub}|$. To illustrate this, we perform a combined $z$-fit of our numerical $B\toπ\ellν$ form-factor data with the experimental branching-fraction measurements leaving the relative normalization as a free parameter; we obtain $|V_{ub}| = 3.61(32) \times 10^{-3}$, where the error includes statistical and systematic uncertainties. This approach can be applied to $B_s\to K \ellν$ decay to determine $|V_{ub}|$ once the process has been measured experimentally. Finally, in anticipation of future measurements, we make predictions for $B \to π\ellν$ and $B_s\to K \ellν$ Standard-Model differential branching fractions and forward-backward asymmetries.

hep-lat↗

arXiv2013

The $B^*Bπ$ coupling with relativistic heavy quarks

We report on a calculation of the $B^*Bπ$ coupling in lattice QCD. The strong matrix element $\langle B π| B^*\rangle$ is directly related to the leading order low-energy constant in heavy meson chiral perturbation theory (HM$χ$PT) for $B$-mesons. We carry out our calculation directly at the $b$-quark mass using a non-perturbatively tuned clover action that controls discretisation effects of order $|\vec{p}a|$ and $(ma)^n$ for all $n$. Our analysis is performed on RBC/UKQCD gauge configurations using domain wall fermions and the Iwasaki gauge action at two lattice spacings of $a^{-1}=1.73(3)$ GeV, $a^{-1}=2.28(3)$ GeV, and unitary pion masses down to 290 MeV. We achieve good statistical precision and control all systematic uncertainties, giving a final result for the HM$χ$PT coupling $g_b = 0.569(48)_{stat}(59)_{sys}$ in the continuum and at the physical light-quark masses. This is the first calculation performed directly at the physical $b$-quark mass and lies in the region one would expect from carrying out an interpolation between previous results at the charm mass and at the static point.

hep-lat↗