In this article, we review the HAL QCD method to investigate baryon-baryon interactions, such as nuclear forces in lattice QCD. We first explain our strategy in detail to investigate baryon-baryon interactions by defining potentials in field theories, such as QCD. We introduce the Nambu-Bethe-Salpeter (NBS) wave functions in QCD for two baryons below the inelastic threshold. We then define the potential from NBS wave functions in terms of the derivative expansion, which is shown to reproduce the scattering phase shifts correctly below the inelastic threshold. Using this definition, we formulate a method to extract the potential in lattice QCD. Secondly, we discuss pros and cons of the HAL QCD method, by comparing it with the conventional method, where one directly extracts the scattering phase shifts from the finite volume energies through the Lüscher's formula. We give several theoretical and numerical evidences that the conventional method combined with the naive plateau fitting for the finite volume energies in the literature so far fails to work on baryon-baryon interactions due to contaminations of elastic excited states. On the other hand, we show that such a serious problem can be avoided in the HAL QCD method by defining the potential in an energy-independent way. We also discuss systematics of the HAL QCD method, in particular errors associated with a truncation of the derivative expansion. Thirdly, we present several results obtained from the HAL QCD method, which include (central) nuclear force, tensor force, spin-orbital force, and three nucleon force. We finally show the latest results calculated at the nearly physical pion mass, m_π ≃ 146 MeV, including hyperon forces which lead to form ΩΩ and NΩ dibaryons.

在本文中，我们回顾了HAL QCD方法以研究重子-重子相互作用，例如晶格QCD中的核力。我们首先通过定义领域理论（例如QCD）中的潜力来详细解释研究重子与重子相互作用的策略。我们在QCD中引入了低于非弹性阈值的两个重子的Nambu-Bethe-Salpeter（NBS）波函数。然后，我们根据导数展开来定义NBS波函数的电势，这表明可以正确地再现非弹性阈值以下的散射相移。使用此定义，我们制定了一种方法来提取晶格QCD中的电势。其次，我们将HAL QCD方法与常规方法进行比较，讨论其优缺点，在这里，人们可以通过Lüscher公式直接从有限的体积能量中提取出散射相移。我们提供了一些理论和数值证据，迄今为止，由于弹性激发态的污染，传统方法与有限体积能量的朴素高原拟合相结合至今未能解决重子-重子相互作用。另一方面，我们表明，通过以能量无关的方式定义电势，可以在HAL QCD方法中避免此类严重问题。我们还将讨论HAL QCD方法的系统学，尤其是与导数展开的截断相关的错误。第三，我们介绍了从HAL QCD方法获得的一些结果，包括（中心）核力，张量，自旋轨道力和三个核子力。米_π＆cong; 146兆电子伏，包括超子力，其导致形成ΩΩ和NΩ dibaryons。