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비섭동 영역에서의 제트-담금질 매개변수 $\hat{q}$
남승일 한국물리학회 2016 새물리 Vol.66 No.6
We investigate the jet-quenching parameter $\hat{q}$ for the quark-gluon plasma (QGP) for $N_c=3$, defined nonperturbatively with the Wilson loop in the light-cone (LC) coordinate, at finite temperature $(T)$. Considering the effective static (heavy) quark-antiquark potential $V_{\bar{Q}Q}=\sigma L+C-A/L$, where $L$ indicates the LC transverse separation between the quarks, we obtain $\hat{q}\approx8V_{\bar{Q}Q}/L^2$. The $T$ dependences for $L$ and other relevant parameters are extracted from the $T$-dependent instanton (trivial-holonomy caloron) length parameters and the lattice quantum chromodynamics (QCD) data. By choosing $L\approx{a}\approx\bar{\rho}_T$, in which $a$ and $\bar{\rho}_T$ denote the lattice spacing and the $T$-dependent average (anti)instanton size, respectively, we find numerically that $\hat{q}=(5\sim25)\,\mathrm{GeV/fm}$ for $T= 0\sim 0.6$ GeV, these values are consistent with other estimates from AdS/CFT and experimental analyses. $\hat{q}$ is produced almost completely by the Coulomb and constant potentials of $V_{\bar{Q}Q}$. We also observe that the ratio $T^3/\hat{q}$ saturates at $\sim4.45\times10^{-2}$ for $T ≳ 0.4$ GeV, indicating a strongly-coupled QGP, and that $\hat{q}$ is proportional to $T^3$ for high $T$. 본 연구는 유한온도 쿼크-글루온 플라즈마에서 중요한 역할을 하는 비섭동 영역에서의 제트-담금질 매개변수($\hat{q}$)를 $N_c=3$의 경우에 대하여, 광원추상의 윌슨 루프를 이용하여 연구하였다. 무거운 쿼크간 광원추상에서 거리가 $L$ 일때, 유효 포텐셜이 $V_{\bar{Q}Q}=\sigma L+C-A/L$로 주어지는 것을 고려하면, $\hat{q}\approx8V_{\bar{Q}Q}/L^2$이 됨을 보인다. $L$과 다른 모형 변수들의 온도 의존성은 자명한 홀로노미(trivial-holonomy)를 가진 칼로론(caloron)과 격자 QCD로부터 결정되어진다. $a$ and $\bar{\rho}_T$를 각각 격자 QCD 간격과 온도에 의존하는 평균적인 인스탄톤의 크기라 하고, 차원 분석을 통해 $L\approx{a}\approx\bar{\rho}_T$를 가정하면, $T=(0\sim0.6)$에서 $\hat{q}=(5\sim25)\,\mathrm{GeV/fm}$로 주어진다. 이 값 은 AdS/CFT 및 실험 분석에서의 다른 추정과 잘 일치한다. 수치결과의 분석을 통해, 포텐셜 $V_{\bar{Q}Q}$중 쿨롱 및 상수 부분의 기여가 가장 중요함을 알 수 있었다. 또한 $T\gtrsim0.4$ GeV의 영역에서 비율 $T^3/\hat{q}$는 약 $4.45\times10^{-2}$에 근접하며, 이는 $\hat{q}$ 가 높은 온도에서 $T^3$의 형태로 거동함을 보여준다.
QCD Topological Susceptibility from the Nonlocal Chiral Quark Model
남승일,Chung-Wen Kao 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.12
We investigate the quantum chromodynamics (QCD) topological susceptibility by using the semi-bosonized nonlocal chiral-quark model (SB-NLQM) for the leading large-Nc contributions. This model is based on the liquid-instanton QCD-vacuum configuration, in which SU(3) flavor symmetry is explicitly broken by the finite current-quark mass (mu,d,ms) (5, 135) MeV. To compute , we derive the local topological charge-density operator Qt(x) from the effective action of SB-NLQM. We verify that the derived expression for in our model satisfies the Witten- Veneziano (WV) and the Leutwyler-Smilga (LS) formulae, and the Crewther theorem in the chiral limit by construction. Once the average instanton size and the inter-instanton distance are fixed with ¯ = 1/3 fm and ¯R = 1 fm, respectively, all the other parameters are determined self-consistently within the model. We obtain = (167.67MeV)4, which is comparable with the empirical value = (175±5MeV)4 whereas it turns out that QL = (194.30MeV)4 in the quenched limit. Thus, we conclude that the value of will be reduced around 10 20% by the dynamical-quark contribution.
Multi-strangeness Productions in Hadron Reactions
남승일,Kim Sang-Ho,Cheoun Myung-Ki,Ahn Jung Keun,Kim Shinhyung 한국물리학회 2023 새물리 Vol.73 No.11
This study examines recent advancements in multi-strangeness production within hadron reactions. The authors introduce their recent research employing the effective Lagrangian method to analyze current experimental data. Notably, the focus is on the S = −2 channel due to its distinct characteristics compared to S = −1 channels. Specifically, we delve into reaction processes like KN → KΞ and KN → KΛΛ, offering potential insights into observing the H-dibaryon. Theoretically, the effective Lagrangian method is intensively employed for this purpose.