Progress in ab initio in-medium similarity renormalization group and coupled-channel method with coupling to the continuum

Abstract Over the last decade, nuclear theory has made dramatic progress in few-body and ab initio many-body calculations. These great advances stem from chiral effective field theory ( $$\chi$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>χ</mml:mi> </mml:math> EFT), which provides an efficient expansion and consistent treatment of nuclear forces as inputs of modern many-body calculations, among which the in-medium similarity renormalization group (IMSRG) and its variants play a vital role. On the other hand, significant efforts have been made to provide a unified description of the structure, decay, and reactions of the nuclei as open quantum systems. While a fully comprehensive and microscopic model has yet to be realized, substantial progress over recent decades has enhanced our understanding of open quantum systems around the dripline, which are often characterized by exotic structures and decay modes. To study these interesting phenomena, Gamow coupled-channel (GCC) method, in which the open quantum nature of few-body valence nucleons coupled to a deformed core, has been developed. This review focuses on the developments of the advanced IMSRG and GCC and their applications to nuclear structure and reactions.