arXiv subjects

HyungJoo Kim

Publications and source records attributed to HyungJoo Kim.

11 recordsLinked to original sources

arXiv2025

Spin structure of spin-1 charmonium states near $T_c$

We investigate the spin structure of the $1^{--}$ and $1^{++}$ charmonium states near the critical temperature using QCD sum rules. To this end, we compute the contribution of the dimension-4 twist-2 gluon operator to the two-point function of heavy vector and axial vector currents in a rotating frame. As temperature increases, the quark spin contribution slightly increases, while the quark orbital angular momentum decreases by a comparable amount. The gluon contribution remains nearly unchanged. These thermal changes cancel each other, ensuring that the total spin is preserved even at finite temperature.

hep-ph↗

arXiv2025

Proton Spin Decomposition via QCD Sum Rules

We present a novel approach for investigating the spin structure of hadrons based on the two-point function in quantum field theory. In a rotating frame, we derive two independent expressions of the two-point function and identify their equivalence, which allows for a complete decomposition of the total spin of a composite system into the angular momenta of its constituent particles. Applying this approach to the proton, we analyze its spin structure in the massless quark limit. Our results indicate that the quark spin contribution accounts for approximately 27$\%$ of the total proton spin at a low-energy scale, significantly deviating from the prediction of the non-relativistic quark model.

hep-ph↗

arXiv2024

$K_{1}^{\pm}$ mesons moving in nuclear matter

Observing the mass shifts of mesons immersed in nuclear matter is interesting, as the changes are expected to shed light on the effects of chiral symmetry breaking on the origin of hadron masses. At the same time, it is important to understand the momentum dependence of the masses for spin-1 mesons, as the changes manifest differently across the two polarization modes. Here, the mass shifts of $K_{1}^{\pm}$ mesons with finite three-momentum in nuclear medium are studied in the QCD sum rule approach. We find that the mass of $K_{1}^{+}$($K_{1}^{-}$) meson is increased(decreased) by the non-trivial momentum effect in both the transverse and longitudinal modes. Specifically, compared to its rest mass in the nuclear medium, in the transverse mode, the mass of $K_{1}^{+}(K_{1}^{-})$ is observed to shift by +2(-55) MeV, while in the longitudinal mode, the mass shift is +13(-11) MeV, all at a momentum of 0.5 GeV. Exploring the medium modifications of $K_{1}$ meson through kaon beams at J-PARC will provide insights on the partial restoration of chiral symmetry in nuclear matter.

nucl-th↗

arXiv2023

Spin-1 quarkonia in a rotating frame and their spin contents

We propose a new way of studying the spin content of a hadron by looking at its response in a rotating frame. By collecting all responses of quarks and gluons in a rotating frame, we describe the spin-rotation coupling of spin-1 quarkonia and thereby reveal their spin contents in a relativistic formalism. We demonstrate that both the perturbative and non-perturbative contributions in the operator product expansion follow a universal formula that identifies the spin-rotation coupling with unit strength. This allows us to recognize the total spin-1 of the vector and axial vector quarkonia in terms of the total angular momentum of quarks and gluons. Specifically, we find the spin contents of $J/ψ$, $χ_{c1}$, $Υ(1S)$, and $χ_{b1}$ are slightly different from the naive quark model picture. For example, the $J/ψ$ is traditionally considered as an S-wave particle, but we find quarks do not carry all of the total spin.

hep-ph↗

arXiv2023

Heavy quarkonium with finite three momentum near $T_c$

We investigate the non-trivial 3-momentum effects on the masses of heavy quarkonium states that are moving in a hot medium using QCD sum rules. For all charmonium states, we observe a negative mass shift near $T_c$ that is less than 3$\%$ at a momentum of 1$\rm{GeV}$. Specifically, we first investigate the difference between the longitudinal and transverse modes of both $J/ψ$ and $χ_{c1}$. We find that the transverse mode of the $J/ψ$ experiences larger modification than the longitudinal mode, while the $χ_{c1}$ has the opposite behavior. By comparing the $η_c$ and $χ_{c0}$, and also the unpolarized $J/ψ$ and $χ_{c1}$, we recognize that the P-wave particles have stronger momentum dependencies on their masses than the S-wave ones. We also find $Υ$(1S) has negligible 3-momentum dependence compared to the charmonium states, e.g. less than 0.01$\%$ even at 1.4$T_c$ and at a momentum of 4$\rm{GeV}$.

hep-ph↗

arXiv2020

The $ϕ$ meson with finite momentum in a dense medium

The dispersion relation of the $ϕ$ meson in nuclear matter is studied in a QCD sum rule approach. In a dense medium, longitudinal and transverse modes of vector particles can have independently modified dispersion relations due to broken Lorentz invariance. Employing the full set of independent operators and corresponding Wilson coefficients up to operator dimension 6, the $ϕ$ meson QCD sum rules are analyzed with changing densities and momenta. The non-trivial momentum dependence of the $ϕ$ meson mass is found to have opposite signs for the longitudinal and transverse modes. Specifically, the mass is reduced by 5 MeV for the longitudinal mode, while its increase amounts to 7 Mev for the transverse mode, both at a momentum scale of 1 GeV. In an experiment which does not distinguish between longitudinal and transverse polarizations, this could in principle be seen as two separated peaks at large momenta. Taking however broadening effects into account, the momentum dependence will most likely be seen as a small but positive effective mass shift and an increased effective width for non-zero momenta.

hep-ph↗

arXiv2018

Transverse momentum broadening and collinear radiation at NLO in the $\mathcal{N}=4$ SYM plasma

We compute O(g) NLO corrections to the transverse scattering kernel and transverse momentum broadening coefficient $\hat{q}$ of weakly-coupled $\mathcal{N}=4$ SYM. Based on this, we also compute NLO correction to the collinear splitting rates. For $\hat{q}$ we find that the NLO/LO ratio is similar to the QCD one, with large NLO corrections. This is contrasted by our findings for the collinear splitting rate, which show a much better convergence in SYM than in QCD, providing further support to earlier expectations that NLO corrections have signs and relative magnitudes controlled by the specifics of the theory. We also compare the ratio of $\hat{q}$ in QCD and in $\mathcal{N}=4$ theory to strong coupling expectations.

hep-ph↗

arXiv2017

Light vector correlator in medium: Wilson coefficients up to dimension 6 operators

As an improvement of the QCD sum rule method to study modifications of light vector mesons in nuclear matter and/or at finite temperature, we calculate the Wilson coefficients of all independent gluonic non-scalar operators up to dimension 6 in the operator product expansion (OPE) of the vector channel for light quarks. To obtain the gluon part of the light quark OPE from the heavy quark one, we also compute the heavy quark expansion of the relevant quark condensates. Together with the results for the quark operators that are already available in the literature, this completes the OPE of the vector channel in a hot or dense medium for operators up to dimension 6.

hep-ph↗

arXiv2017

Wilson coefficients of dimension 6 gluon operators with spin indices in the heavy quark current correlation functions

We calculate the Wilson coefficients of dimension 6 gluon operators with spin indices in the two point correlation function of the heavy scalar, pseudoscalar, and axialvector currents. Our result completes the list of all Wilson coefficients of gluon operators up to dimension 6 for the correlation functions between heavy quark currents without derivatives. We then use the result to investigate the stability of the QCD sum rule results for the $η_c$, $J/Ψ$, $χ_{c0}$, and $χ_{c1}$ mesons near $T_c$. While the inclusion of the dimension 6 operators increases the stability of the sum rules for all currents, all of them break down slightly above $T_c$ with that for the $J/ψ$ persisting to relatively highest temperature.

hep-ph↗

arXiv2015

Temperature dependence of dimension 6 gluon operators and their effects on Charmonium

Starting from an earlier representation of the independent dimension 6 gluon operators in terms of color electric and magnetic fields, we estimate their changes near the critical temperature $T_c$ using the temperature dependence of the dimension 4 electric and magnetic condensates extracted from pure gauge theory on the lattice. We then improve the previous QCD sum rules for the $J/ψ$ mass near $T_c$ based on dimension 4 operators, by including the contribution of the dimension 6 operators to the OPE. We find an enhanced stability in the sum rule and confirm that the $J/ψ$ will undergo an abrupt change in the property across $T_c$.

hep-ph↗

arXiv2015

Renormalization of dimension 6 gluon operators

We identify the independent dimension 6 twist 4 gluon operators and calculate their renormalization in the pure gauge theory. By constructing the renormalization group invariant combinations, we find the scale invariant condensates that can be estimated in nonperturbative calculations and used in QCD sum rules for heavy quark systems in medium.

hep-ph↗