Baryon interactions play an essential role to understand nuclear phenomena. The determination of baryon interactions based on the fundamental theory, QCD, is one of the most challenging issue in nuclear physics. In this talk, I review the theoretical formulation, HAL QCD method, to obtain baryon forces from the Nambu-Bethe-Salpeter (NBS) four-point correlators measured on the lattice. By using the method, I will show the results of various types of baryon interactions and discuss the possibility of dibaryon formations.

In this talk, we will discuss the possibility that some of those particles whose quantum numbers are 1^-- and masses are between 4.0 and 4.8 GeV are hybrid mesons. We will also consider that there could exist bottom-quark equivalents of those particles, introducing two different parameter sets. I will show that if there exists a hybrid charmonium, its constituent gluon is magnetic; also I will argue that we could not exclude the possibility that Υ(10860) is the first excited state of a hybrid bottomonium. If time permits, I will talk about possible future work and challenges relating to hybrid mesons.

We propose a tetraquark mixing framework for light mesons in the J^P = 0⁺ channel, using the diquark-antidiquark model. In particular, we propose two types of tetraquark with different spin configuration, |J, J₁₂ , J₃₄⟩ = |000⟩, |011⟩, where J is the spin of the tetraquark, J₁₂ the diquark spin, J₃₄ the antidiquark spin. The two types of tetraquark appear to have an interesting correspondence with the presence of two nonets in PDG, f₀(500), f₀(980), a₀(980), K₀^∗(800) in the light nonet, and f₀(1370), f₀(1500), a₀(1450), K₀^∗(1430) in the heavy nonet. Indeed, the two tetraquarks mix strongly through the hyperfine color-spin interaction and the eigenstates that diagonalize the hyperfine masses can be identified with the two nonets in PDG. We report that their hyperfine mass splitting can generate the mass gap between the two nonets qualitatively. We also discuss an interesting signature in the decays of our tetraquark model.
Reference: PRD 97,094005 (2018), Hungchong Kim, K.S.Kim, M.K.Cheoun, M.Oka.

In this talk I will present my latest two projects. First, I have been working with Denis Parganlija to examine the excited meson spectrum using the extended Linear Sigma Model (eLSM) [1]. When working with an effective model like the eLSM, one has to identify experimentally measured resonances with certain fields in the model. This is a non trivial task, since there is no obvious one-to-one correspondence. The main result was predicting the mass and decay widths of certain excited mesons. This plays a part in better understanding the current meson spectrum and connecting it to the current theoretical knowledge of the strong interaction. Second, I will present the results of my Master's thesis, performed under the supervision of Wolfgang Lucha. In this work, we explored the instantaneous Bethe-Salpeter equation in connection with in-hadron condensates. It was first suggested by Brodsky and Shrock [2] that in-hadron condensates can help solve an ongoing debate about the cosmological constant, which is predicted to be 45 orders of magnitude larger than experimentally measured. We investigated the validity of the Gell-Mann–Oakes–Renner (GMOR) relation in the specific case where the vacuum condensate is replaced by an in-hadron condensate. Our results showed that the generalized GMOR relation is valid in the chiral limit. This is further evidence that the usage of in-hadron condensates leads towards a resolution of the discrepancy concerning the cosmological constant.
REFERENCES: [1] arXiv:1612.09218v2, [2] arXiv:0905.1151

理論による実験物理の最先端としての立場を確固たるものとしている格子QCDであるが、「より精密なリファレンススケールの設定」や「格子上のエネルギー運動量テンソルの構成法」のような例を筆頭に解決すべき問題が残されていた。これらの例は、現在、「ヤン-ミルズ勾配流」と呼ばれる手法を格子QCDへと応用することによって飛躍的な進展が得られている。しかし、実用上の問題として「連続理論」と「格子理論」のズレである「離散化誤差」が、ヤン-ミルズ勾配流の適用によって従来のものから大きく変化してしまう可能性が指摘されている。本セミナーでは、ヤン-ミルズ勾配流の格子計算への応用について、離散化誤差という観点から話を展開し、最終的に博士課程の成果である「ツリーレベル離散化誤差の抑制法」について説明したい。