arXiv subjects

Kenshi Kuroki

Publications and source records attributed to Kenshi Kuroki.

6 recordsLinked to original sources

arXiv2026

Tensor-polarized twist-3 distribution function $f_{LT}$ of spin-1 deuteron

We investigate the twist-2 and twist-3 tensor-polarized partonic structures of the spin-1 deuteron. Using the operator product expansion with local operators, we derive a Wandzura-Wilczek (WW)-like twist-2 relation between the tensor-polarized twist-2 quark distribution $f_{1LL}$ and the twist-3 distribution $f_{LT}$, together with a Burkhardt-Cottingham (BC)-like sum rule. The local-operator formalism makes the Lorentz structure and rotational invariance manifest and provides useful constraints on the twist-3 sector. We then use a phenomenological parametrization of the twist-2 distribution $f_{1LL}(x)$, constrained by HERMES data on the deuteron structure function $b_1$ at $Q^2=2.5~\text{GeV}^2$, to quantitatively estimate the twist-3 distribution $f_{LT}(x)$ within the WW approximation. The resulting $f_{LT}(x)$ has a shape and magnitude comparable to those of $f_{1LL}(x)$, indicating that subleading-twist effects may be relevant for future experiments at relatively low $Q^2$. In this contribution, we summarize the theoretical derivation of the WW-like relation and BC-like sum rule and present a phenomenological estimate of the tensor-polarized twist-3 quark distribution $f_{LT}$ in the deuteron.

hep-ph↗

arXiv2026

Twist-2 relations for the twist-3 tensor-polarized distribution function $f_{LT}$ of a spin-1 hadron by the operator-product-expansion method

In a spin-1 hadron, tensor-polarized parton distribution functions (PDFs) exist. The twist-2 function is $f_{1LL}$ and a twist-3 one is $f_{LT}$. Because an experiment is under preparation at the Thomas Jefferson National Accelerator Facility (JLab) to measure the cross section of electron-deuteron deep inelastic scattering with the tensor-polarized deuteron target, these PDFs need to be understood theoretically. Especially, measurements will be done in a relatively low-$Q^2$ region at JLab, so that twist-3 contributions could become sizable in the cross section. In a previous work, a twist-2 relation was derived for $f_{LT}$ in terms of $f_{1LL}$ by using a nonlocal operator, and it corresponds to the Wandzura-Wilczek (WW) relation between $g_1$ and $g_2$. In addition, another relation similar to the Burkhardt-Cottingham (BC) sum rule was obtained. It is known that a formal way to derive the WW relation and the BC sum rule is to use the operator product expansion (OPE) with local operators. In this work, the WW-like relation and the BC-like sum rule for $f_{LT}$ are derived by using the local OPE method as a reliable independent way to establish these relations.

hep-ph↗

arXiv2026

Tensor-polarized parton distribution functions of the deuteron by a convolution model

Tensor-polarized parton distribution functions (PDFs) are calculated for the deuteron by using a convolution formalism, where the tensor-polarized PDFs are given by the corresponding nucleon's unpolarized PDFs convoluted with the tensor-polarized nucleon momentum distribution in the deuteron. These distributions are obtained at $Q^2=2.5$ GeV$^2$ in order to compare with the tensor-polarized PDFs which were determined by HERMES $b_1$ data. The obtained distributions are very different from the ones determined from the HERMES data, which indicates further studies are needed to clarify the difference, possibly by considering a new mechanism beyond the simple bound system of a proton and a neutron. The obtained PDFs $δ_T q $ and $δ_T \bar q$ are converted to the PDFs of the Trento convention $f_{1LL}^{\, q}$ and $f_{1LL}^{\, \bar q}$, and they are used for estimating the twist-3 PDFs $f_{LT}^{\, q}$ and $f_{LT}^{\, \bar q}$ by using a Wandzura-Wilczek-like relation. Because deep-inelastic-scattering experiments are under preparation for structure functions with a tensor-polarized deuteron target at the Thomas Jefferson National Accelerator Facility, and a Drell-Yan experiment will be possible at hadron accelerator facilities, such as the Fermi National Accelerator Laboratory, the obtained tensor-polarized PDFs will be tested experimentally.

hep-ph↗

arXiv2026

Tensor-polarized twist-3 parton distribution functions $f_{LT}(x)$ for the spin-1 deuteron by using twist-2 relations

Tensor-polarized twist-3 parton distribution functions (PDFs) $f_{LT}(x)$ are calculated for the spin-1 deuteron by using twist-2 relations, which are similar to the Wandzura-Wilczek relation and the Burkhardt-Cottingham sum rule in the spin-1/2 nucleon, together with tensor-polarized twist-2 PDFs $f_{1LL}(x)$. The PDFs are shown for $f_{LT}(x)$ at $Q^2 =2.5$ GeV$^2$, where the tensor-polarized PDFs $f_{1LL}(x)$ are provided. The $x$-dependence of $f_{LT}(x)$ is similar to $f_{1LL}(x)$, and the magnitude of $f_{LT}(x)$ is roughly of the order of $f_{1LL}(x)$. In experiments at the Thomas Jefferson National Accelerator Facility (JLab), higher-twist effects could be sizable because $Q^2$ values are not very large in comparison with the hadronic scale of 1 GeV$^2$. Therefore, the JLab experiments could provide a good opportunity to investigate the twist-3 distributions $f_{LT}(x)$ in addition to the twist-2 ones $f_{1LL}(x)$. Furthermore, these tensor-polarized PDFs could be investigated at future Electron-Ion Colliders (EICs) and hadron accelerator facilities such as the Fermi National Accelerator Laboratory (Fermilab), the Nuclotron-based Ion Collider fAcility (NICA), and the Large Hadron Collider (LHC).

hep-ph↗

arXiv2024

p--$ϕ$ femtoscopic correlation analysis using a dynamical model

We analyse the p--$ϕ$ correlation functions in high-multiplicity proton+proton collisions at the LHC using a dynamical model, DCCI2, and discuss the effects of collision dynamics on the p--$ϕ$ femtoscopic study. Collision dynamics, such as collective expansion and hadronic rescatterings, leads to the relative momentum-dependent non-Gaussian source functions. This results in deviations in the correlation functions compared to those using the Gaussian source function adopted in existing studies. Our analysis shows the importance of using the source functions that reflect more realistic collision dynamics for future precision analysis of hadron interactions via femtoscopy.

hep-ph↗

arXiv2023

Hydrodynamic fluctuations and ultra-central flow puzzle in heavy-ion collisions

One of the long-standing problems in the field of high-energy heavy-ion collisions is that the dynamical models based on viscous hydrodynamics fail to describe the experimental elliptic flow $v_2$ and the triangular flow $v_3$ simultaneously in ultra-central collisions. The problem, known as the "ultra-central flow puzzle", is specifically that hydrodynamics-based models predict the flow ratio of the two-particle cumulant method $v_2\{2\}/v_3\{2\} > 1$ while $v_2\{2\}/v_3\{2\} \sim 1$ in the experimental data. In this Letter, we focus on the effects of hydrodynamic fluctuations during the space-time evolution of the QGP fluid on the flow observables in the ultra-central collisions. Using the (3+1)-dimensional integrated dynamical model which includes relativistic fluctuating hydrodynamics, we analyze the anisotropic flow coefficients $v_n\{2\}$ in 0-0.2% central Pb+Pb collisions at $\sqrt{s_\text{NN}}=2.76~\text{TeV}$. We find that the hydrodynamic fluctuations decrease the model overestimate of $v_2\{2\}/v_3\{2\}$ from the experimental data by about 19% within the present setup of $η/s = 1/2π$. This means that the hydrodynamic fluctuations qualitatively have an effect to improve the situation for the puzzle, but the effect of the hydrodynamic fluctuations alone is quantitatively insufficient to resolve the puzzle. The decrease of the ratio largely depends on the shear viscosity $η/s$, which calls for future comprehensive analyses with, for example, a realistic temperature-dependent viscosity.

nucl-th↗