arXiv subjects

Yuji Koike

Publications and source records attributed to Yuji Koike.

68 records · Page 4Linked to original sources

arXiv2000

Hyperon Polarization in Inclusive Hadronic Production

A QCD formula for the polarization in the large-p_T Λhyperon production in the unpolarized nucleon-nucleon collision at large x_F is derived. We focus on the mechanism in which the chiral-odd spin-independent twist-3 quark distribution E_F(x,x) becomes the source of the transversely polarized quarks fragmenting into the polarized Λ. A simple model estimate for that contribution shows the possibility that it gives rise to a sizable Λpolarization.

hep-ph↗

arXiv2000

Estimate of a Chiral-Odd Contribution to Single Transverse-Spin Asymmetry in Hadronic Pion Production

We present an estimate of a chiral-odd contribution to the single transverse-spin asymmetry in the large-$p_T$ pion production in the nucleon-nucleon collision. In this contribution the transversity distribution and the chiral-odd spin-independent twist-3 distribution appear. Because of the smallness of the corresponding hard cross section, this term turned out to be negligible in all kinematic regions compared with the chiral-even contribution.

hep-ph↗

arXiv2000

Chiral-Odd Contribution to Single-Transverse Spin Asymmetry in Hadronic Pion Production

A formula for the single transverse spin asymmetry in the large-$p_T$ pion production in the nucleon-nucleon collision is derived. We focuss on the chiral-odd contribution where the transversity distribution and the chiral-odd spin-independent twist-3 distribution contributes. This contribution is expected to give rise to a large effect at $x_F\to -1$.

hep-ph↗

arXiv1999

Twist-3 effects in polarized Drell-Yan and semi-inclusive DIS

Two twist-3 processes are discussed. We first present a simple estimate of the longitudinal-transverse spin asymmetry in the polarized Drell-Yan process. We next derive a cross section for the semi-inclusive production of a polarized spin-1/2 baryon in the DIS of an unpolarized electron off the polarized nucleon.

hep-ph↗

arXiv1999

A_{LT} in the Nucleon-Nucleon Polarized Drell-Yan Process

We present a leading order (LO) estimate for the longitidinal-transverse spin asymmetry (A_{LT}) in the nucleon-nucleon polarized Drell-Yan process at RHIC and HERA-$\vec{N}$ energies in comparison with A_{LL} and A_{TT}. A_{LT} receives contribution from g_1, the transversity ditribution h_1, and the twist-3 distributions g_T and h_L. For the twist-3 contribution we use the bag model prediction evolved to a high energy scale by the large-N_c evolution equation. We found that A_{LT} (normalized by the asymmetry in the parton level) is much smaller than the corresponding A_{TT}. Twist-3 contribution given by the bag model also turned out to be negligible.

hep-ph↗

arXiv1999

Hadron Structures and Perturbative QCD

In the first part of this talk, I will summarize recent developments in the study of the chiral-odd spin-dependent parton distributions h_1(x,Q^2) and h_L(x,Q^2) of the nucleon, in particular, (i) Next-to- leading order Q^2 evolution of h_1(x,Q^2) and (ii) Leading order Q^2 evolution of the twist-3 distribution $h_L(x,Q^2)$ and the universal simplification of the Q^2 evolution of all the twist-3 distributions in the large $N_c$ limit. The second part of this talk will be devoted to a systematic analysis on the light-cone distribution amplitudes of vector mesons ($ρ$, $ω$, $ϕ$, $K^*$ etc) relevant for exclusive processes producing these mesons. In particular, twist-3 distribution amplitudes are discussed in detail.

hep-ph↗

arXiv1998

A_{LT} in the polarized Drell-Yan process at RHIC and HERA energies

hep-ph↗

arXiv1998

NLO $Q^2$-evolution of the nucleon's transversity distribution $h_1(x, Q^2)$

We present a calculation of the two-loop anomalous dimension for the transversity distribution $h_1(x,Q^2)$, $γ^{h(1)}_n$, in the MS scheme of the dimensional regularization. Because of the chiral-odd nature, $h_1$ does not mix with the gluon distributions, and thus our result is the same for the flavor-singlet and nonsinglet distributions. At small $n$ (moment of $h_1$), $γ^{h(1)}_n$ is significantly larger than $γ^{f,g(1)}_n$ (the anomalous dimension for the nonsinglet $f_1$ and $g_1$), but approaches $γ^{f,g(1)}_n$ very quickly at large $n$, keeping the relation $γ^{h(1)}_n > γ^{f,g(1)}_n$. This feature is in parallel to the relation between the one-loop anomalous dimension for $f_1$ $(g_1)$ and $h_1$. We also show that this difference in the anomalous dimension between $h_1$ and $g_1$ leads to a drastic difference in the $Q^2$-evolution of those distributions in the small $x$ region.

hep-ph↗

arXiv1998

Recent Developments in Perturbative QCD: Q^2 Evolution of Chiral-Odd Distributions h_1(x,Q^2) and h_L(x,Q^2)

After reviewing QCD definitions of the chiral-odd spin-dependent parton distributions $h_1(x,Q^2)$ and h_L(x,Q^2), I will summarize the main feature of the recent two results in perturbative QCD: (i) Next-to-leading order $Q^2$ evolution of h_1(x,Q^2). (ii) Leading order Q^2 evolution of the twist-3 distribution h_L(x,Q^2) and the universal simplification of the Q^2 evolution of all the twist-3 distributions in the large N_c limit.

hep-ph↗

arXiv1997

QCD sum rules for ρ, ω, ϕmeson-nucleon scattering lengths and the mass shifts in nuclear medium

A new QCD sum rule analysis on the spin-isospin averaged $ρ$, $ω$ and $ϕ$ meson-nucleon scattering lengths is presented. By introducing the constraint relation on the the low energy limit of the vector-current nucleon forward scattering amplitude, we get $a_ρ=-0.47\pm 0.05$ fm, $a_ω=-0.41\pm 0.05$ fm and $a_ϕ=-0.15\pm 0.02$ fm, which suggests that these V-N interactions are attractive. It is also proved that the previous studies on the mass shift of these vector mesons in the nuclear medium are essentially the ones obtained from these scattering lengths in the linear density approximation.

nucl-th↗

arXiv1997

Next-to-leading order Q^2-evolution of the transversity distribution h_1(x, Q^2)

We present a calculation of the two-loop anomalous dimension for the transversity distribution h_1(x,Q^2), $γ^{h(1)}_n$, in the MS scheme of the dimensional regularization. Due to the chiral-odd nature, h_1 does not mix with the gluon distributions, and thus our result is the same for the flavor-singlet and nonsinglet distributions. At small n (moment of h_1), $γ^{h(1)}_n$ is significantly larger than $γ^{f(1)}_n$ (the anomalous dimension for the nonsinglet f_1), but approaches $γ^{f(1)}_n$ very quickly at large n, keeping the relation $γ^{h(1)}_n > γ^{f(1)}_n$. This feature is in parallel to the relation between the one-loop anomalous dimension for f_1 and h_1.

hep-ph↗

arXiv1997

Bag Model Prediction for the Nucleon's Chiral-odd Twist-3 Distribution h_L(x,Q^2) at High Q^2

We study the Q^2 evolution of the nucleon's chiral-odd twist-3 distribution h_L(x,Q^2) starting from the MIT bag model calculation. A simple GLAP equation for h_L(x,Q^2) obtained at large N_c is used for the Q^2 evolution. The correction due to the finite value of N_c is O(1/N_c^2)\sim 10% level. It turns out that the twist-3 contribution to h_L(x,Q^2) is significantly reduced at Q^2=10 GeV^2 in contrast to the g_2(x,Q^2) case. This is due to the fact that the corresponding anomalous dimension for h_L is larger than that for g_2 at small n (spin).

hep-ph↗

arXiv1996

$Q^2$ evolution of chiral-odd twist-3 distribution $e(x,Q^2)$

We study the $Q^2$ dependence of the chiral-odd twist-3 distribution $e(x,Q^2)$.The anomalous dimension matrix for the corresponding twist-3 operators is calculated in the one-loop level. This study completes the calculation of the anomalous dimension matrices for all the twist-3 distributions together with the known results for the other twist-3 distributions $g_2(x,Q^2)$ and $h_L(x,Q^2)$. We also have confirmed that in the large $N_c$ limit the $Q^2$-evolution of $e(x,Q^2)$ is wholely governed by the lowest eigenvalue of the anomalous dimension matrix which takes a very simple analytic form as in the case of $g_2$ and $h_L$.

hep-ph↗

arXiv1993

Octet Baryons at Finite Temperature: QCD Sum Rules vs. Chiral Symmetry

Correlators of the octet baryons in the hot pion gas are studied in the framework of the QCD sum rule. The condensates appearing in the OPE side of the correlators become T-dependent through the interaction with thermal pions. We present an explicit demonstration that the $O(T^2)$-dependence of the condensates is completely compensated by the change of the pole residue and the $π+ B \rightarrow B'$ scattering effect in the spectral functions. Therefore the baryon masses are constant to this order, although $\langle\bar{u}u\rangle_T\simeq\langle\bar{u}u\rangle_0(1-T^2/8f_π^2)$, which is consistent with the chiral symmetry constraint by Leutwyler and Smilga.

hep-ph↗