Recent development in theoretical studies of hyperon-nucleon interaction

Abstract

Hypernuclear physics is the study of hypernuclei, their decays and productions, and the role they play in other related fields. It has always been at the frontier of experimental and theoretical nuclear physics since the quantum number strangeness was introduced and the first Λ hypernuclus was discovered in 1953. In recent years, open questions such as the large change symmetry breaking in A =4 Λ hypernuclei, the overbinding problem of A =5 Λ hypernucleus, the existence of the H-dibaryon and the hyperon puzzle in neutron stars have attracted a lot of attention. Today facilities like J-PARC, KEK, JLab, MAMI and COSY allow one to study the properties of hypernuclei with a precision and scope hitherto impossible. The experiments focus not only on the spectroscopy and weak decays of hypernuclei with strangeness S= − 1 and S = − 2, but also on the fundamental ΣN cross sections. In the meantime, theoretical techniques of few- and many-body calculations for hypernuclei have made steady progress, such as the Gaussian expansion method, the lattice QCD simulations and the Dirac-Brueckner-Hartree-Fock approach. Hyperon-nucleon interaction is the key input of the hypernuclear few- and many-body calculations. It plays a fundamental role in the microscopic understanding of hypernuclear physics. Meanwhile, it can also help improve our understanding of the role of strangeness in particle and nuclear physics, as well as the SU(3) symmetry and its breaking. In this paper, we first review the origin of hypernuclear physics and enmumerrate the aforementioned open questions of current interest. These outstanding issues reflect that the hyerpon-nucleon interaction is not fully understood so far. Then we discuss at length the history and current status of theoratical studies of hyperon-nucleon interaction, which are mainly performed in phenomenological models, lattice quantumchromo dynamics (lattice QCD) simulations and chiral effective field theory. The construction of phenomenological models, such as meson exchange models and quark models, has a rather long history. However, they predict very different results even for some of the low-energy phase shifts and scattering lengths, owing to the rather loose constraint from the small number of hyperon-nucleon scattering data. Lattice QCD simulations have made impressive progress since the 21st century, which provide an ab-initio numerical solution to QCD from first principles. With the ever-growing computing power and evolving numerical algorithms, lattice QCD simulations are getting close to the physical point (but still with large error bars). As the effective theory of low-energy QCD, chiral effective field theory has proven to be a useful tool in studies of low-energy strong interaction phenomena. The main feature of this approach is that by using a proper power counting scheme, one can improve calculations systematically by going to higher orders in powers of external momenta and light quark masses, and meantime the uncertainties of any given order. Furthermore, three- and four-body forces can be derived in a consistent manner. Studies of hadron-hadron interaction in chiral effective field theory have made remarkable progress in the past two decades and in the last part of this article we discuss the recent construction of hyperon-nucleon interaction in chiral effective field theory in detail.