BΛ(HΛ5e) from short range effective field theory

Abstract

We present an effective field theory (EFT) at leading order to describe light single-Λ hypernuclei. Owing to the weak Λ binding and to the ΛN short interaction range, meson exchange forces are approximated by contact interactions within a pionless EFT(πEFT) where the only degrees of freedom are baryons. At leading order, the Λ-nuclear interaction contains two 2-body (singlet and triplet) and three 3-body interaction terms, a total of 5 terms associated with 5 coupling strengths or low energy constants (LECs). We adopt the 2-body LECs from hyperon-nucleon scattering data and interaction models that constrain the ΛN scattering lengths, while the 3-body LECs are adjusted using both 3-body and 4-body hypernuclear binding energies. To calculate the binding energies for A-body systems with A>2, we expand the wavefunctions using a correlated Gaussian basis. The stochastic variational method is employed to select the non-linear parameters. The resulting πEFT is then applied to calculate the Λ separation energy in HΛ5e, where the adjusted 3-body interactions largely resolve the known overbinding problem of HΛ5e.