Ab Initio NCSM/RGM for Three-Cluster Structure Systems*

The $ab~initio$ no-core shell model/resonating group method (NCSM/RGM) introduced in [1] is a technique able to describe both structure and reactions in light nuclear systems. This approach combines a microscopic cluster technique with the use of realistic inter-nucleon interactions and a consistent microscopic description of the nucleon clusters. In this work, we introduce the treatment of three-body cluster dynamics, making the approach suitable for the investigation of systems presenting such structure. We present results obtained for $^6$He within a $^4$He(g.s.)+$n$+$n$ basis [2]. We find a bound state in the $J^{\pi}T=0^+1$ channel, corresponding to the $^6$He ground state. On the continuum, we obtained the experimentally well-known $2^+_1$ resonance as well as the second low-lying $2_2^+$ resonance recently measured at GANIL [3]. In addition, we predict low-lying resonances in $J^{\pi}$= $1^+$, $2^-$, and $0^-$ channels. We will present initial results including core excitations through the no-core shell model with continuum coupling and for the structure of $^5$H within a $^3$H+$n$+$n$ basis.\\[4pt] [1] S.Quaglioni and P. Navr\'atil, PRL 101, 092501 (2008), [2] S. Quaglioni, C.Romero-Redondo, P. Navr\'atil, PRC 88, 034320 (2031), [3] X. Mougeot $et~al$, Phys. Lett. B 718