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Hiroyuki Kawamura

Publications and source records attributed to Hiroyuki Kawamura.

27 records · Page 2Linked to original sources
arXiv2002

B meson light-cone wavefunctions in the heavy quark limit

We present a systematic study of the B meson light-cone wavefunctions in QCD in the heavy-quark limit. We construct model-independent formulae for the light-cone wavefunctions in terms of independent dynamical degrees of freedom, which exactly satisfy the QCD equations of motion and constraints from heavy-quark symmetry. The results demonstrate novel behaviors of longitudinal as well as transverse momentum distribution in the B mesons.

hep-ph↗
arXiv2002

Transverse Momentum Distribution in the B Mesons in the Heavy-quark Limit: the Wandzura-Wilczek Part

In the heavy-quark limit, the valence Fock-state components in the B mesons are described by a set of two light-cone wavefunctions. We show that these two wavefunctions obey simple coupled differential equations, which are based on the equations of motion in the Heavy Quark Effective Theory (HQET), and the analytic solutions for them are obtained. The results generalize the recently obtained longitudinal-momentum distribution in the Wandzura-Wilczek approximation by including the transverse momenta. We find that the transverse momentum distribution depends on the longitudinal momentum of the constituents, and that the wavefunctions damp very slowly for large transverse separation between quark and antiquark.

hep-ph↗
arXiv2002

B meson light-cone distribution amplitudes in the heavy-quark limit

We investigate the B meson light-cone distribution amplitudes in the heavy-quark limit which are relevant for the QCD factorization approach for the exclusive B meson decays. We derive exact relations between two- and three-particle distribution amplitudes from the QCD equations of motion and heavy-quark symmetry constraint. As solution of these relations, we give representations for the quark-antiquark distribution amplitudes in terms of independent dynamical degrees of freedom. In particular, we find that the Wandzura-Wilczek-type contributions are determined uniquely in analytic form in terms of \barΛ, a fundamental mass parameter of heavy-quark effective theory, and that both leading- and higher-twist distribution amplitudes receive the contributions of multi-particle states with additional gluons.

hep-ph↗
arXiv2001

B meson light-cone distribution amplitudes and heavy-quark symmetry

We present a systematic study of the B meson light-cone distribution amplitudes which are relevant for the QCD factorization approach for the exclusive B meson decays. We construct representations for the quark-antiquark distribution amplitudes in terms of independent dynamical degrees of freedom, which exactly satisfy the QCD equations of motion and constraints from heavy-quark symmetry.

hep-ph↗
arXiv2001

Electroweak Sudakov corrections at 2 loop level

In processes at the energy much higher than electroweak scale, weak boson mass act as the infrared cutoff in weak boson loops and resulting Sudakov log corrections can be as large as 10%. Since electroweak theory is off-diagonally broken gauge theory, its IR structure is quite different from that of QCD. We briefly review recent developments on electroweak Sudakov and discuss on the exponentiation of Sudakov double logs and explicit 2 loop calculations in Feynman gauge.

hep-ph↗
arXiv1996

Renormalization of Twist-4 Operators in QCD Bjorken and Ellis-Jaffe Sum Rules

The QCD effects of twist-4 operators on the first moment of nucleon spin-dependent structure function $g_1(x, Q^2 )$ are studied in the framework of operator product expansion and renormalization group method. We investigate the operator mixing through renormalization of the twist-4 operators including those proportional to the equation of motion by evaluating off-shell Green's functions in the usual covariant gauge as well as in the background gauge. Through this procedure we extract the one-loop anomalous dimension of the spin 1 and twist-4 operator which determines the logarithmic correction to the $1/Q^2$ behavior of the contribution from the twist-4 operators to the first moment of $g_1(x,Q^2)$.

hep-ph↗
arXiv1996

QCD Analysis of Twist-4 Contributions to the $g_1$ Structure Functions

We analyze the twist-4 contributions to Bjorken and Ellis-Jaffe sum rules for spin-dependent structure function $g_1(x, Q^2 )$. We investigate the anomalous dimensions of the twist-4 operators which determine the logarithmic correction to the $1/Q^2$ behavior of the twist-4 contribution by evaluating off-shell Green's functions in both flavor non-singlet and singlet case. It is shown that the EOM operators play an important role to extract the anomalous dimensions of physical operators. The calculations to solve the operator mixing of higher-twist operators are given in detail.

hep-ph↗
arXiv1994

Target Mass Effects in QCD Bjorken Sum Rule

We investigate the target mass effects in QCD Bjorken sum rule. The magnitude of the target mass correction is estimated in a variety of methods employing positivity bound as well as the experimental data for the asymmetry parameters. It turns out that the target mass correction is sizable at low $Q^2$ of the order of a few GeV$^2$, where the QCD correction is significant. We show that there exists uncertainty due to target mass effects in determining the QCD effective coupling constant $α_s(Q^2)$ from the Bjorken sum rule.

hep-ph↗