Yuichiro Kiyo

quarkonium 1S spectrum in large-β0 approximation and renormalon cancellation

Abstract Presently the quarkonium spectrum, written in terms of the quark MS -mass, is known at O (α S 3 m) accuracy. We point out that in order to achieve O (α S 4 m) accuracy it is sufficient to calculate further (I) the O (α S 4 m) relation between the MS -mass and the pole-mass, and (II) the binding energy at O (α S 5 m) in the large- β 0 approximation. We calculate the latter correction analytically for the 1 S -state and study its phenomenological implications.

Top quark mass determination and O ( α S 5 m ) correction to the toponium 1 S energy level

Recently the full O(alpha_S^5 m, alpha_S^5 m log(alpha_S)) correction to the heavy quarkonium 1S energy level has been computed (except the a_3-term in the QCD potential). We point out that the full correction (including the log(alpha_S)-term) is approximated well by the large-beta_0 approximation. Based on the assumption that this feature holds up to higher orders, we discuss why the top quark pole mass cannot be determined to better than O(Lambda_{QCD}) accuracy at a future e^+e^- collider, while the MS-bar mass can be determined to about 40 MeV accuracy (provided the 4-loop MSbar-pole mass relation will be computed in due time).

Azimuthal angular dependence of decay lepton in \(e^+ e^- \to t \bar{t}\)

Abstract. We discuss top quark production and its subsequent decay as used for searching new physics at lepton colliders. The angular dependence of the decay leptons is calculated including both QCD corrections and anomalous

Off-shell suppression of renormalons in non-relativistic QCD boundstates

\gamma / Z - t \bar{t}

The polarized photon structure function g1γ(x,Q2) in massive parton model in NLO

couplings. The off-diagonal spin basis for the top and anti-top quarks is shown to be useful to probe the anomalous couplings.

Revisiting W Production at RHIC

Abstract We study an effect of the off-shellness of the quark and antiquark inside a heavy quarkonium system on IR renormalons contained in the perturbative computations of the quarkonium energy levels. We demonstrate that, when the off-shellness p Q 2 − m Q 2 ∼ α S 2 m Q 2 is larger than m Q Λ QCD , renormalons in the energy levels as calculated in perturbative QCD are suppressed by a factor Λ QCD /( α S 2 m Q ) as compared to those in 2 m pole + V QCD ( r ). In this case the residual O (Λ QCD 4 ) renormalon has the same dimension as that of the leading gluon-condensate contribution.

Revisiting W γ Production at RHIC

We investigate the one-gluon-exchange (ααs) corrections to the polarized real photon structure function g1γ(x,Q2) in the massive parton model. We employ a technique based on the Cutkosky rules and the reduction of Feynman integrals to master integrals. The NLO contribution is noticeable at large x and does not vanish at the threshold of the massive quark pair production due to the Coulomb singularity. It is found that the first moment sum rule of g1γ is satisfied up to the NLO.

Spin correlations and azimuthal angular dependence in e+e−→tt̄

We discuss Wγ production in polarized pp collisions at the RHIC energy. We point out that the RHIC collider has two advantages over other hadron colliders to measure the characteristic features of Wγ production: (1) the RHIC energy is not too high, and (2) polarized beams are available. We calculate the tree level cross section for Wγ production using a generic spin basis for W and study both the angular dependence and spin correlation.

CPviolation in the kaon system in a supersymmetric SU(5) model with seesaw-induced neutrino masses

We discuss Wγ production in polarized pp collisions at the RHIC energy. We point out that the RHIC collider has two advantages over other hadron colliders to measure the characteristic features of Wγ production: (1) the RHIC energy is not too high, and (2) polarized beams are available. We calculate the tree level cross section for Wγ production using a generic spin basis for W and study both the angular dependence and spin correlation.

Erratum to “The polarized photon structure function g1γ(x,Q2) in massive parton model in NLO” [Phys. Lett. B 707 (1) (2012) 146–150]

We discuss top quark production and its subsequent decay at e+e− colliders including QCD corrections and anomalous coupling in γ/Z−t−t vertices. In off-diagonal spin basis, azimuthal angular distribution of decay product of polarized top quarks is shown to be useful to probe γ/Z−t−t vertices.