PARTICLE PHYSICS | REVIEW ARTICLE Looking for a hidden sector in exotic Higgs boson decays with the ATLAS experiment i

1 * ,ii Abstract: The nature of dark matter (DM) is one of the most intriguing questions in particle physics. DM can be postulated to be part of a hidden sector whose inter- actions with the visible matter are not completely decoupled. The discovery of a fundamental scalar particle compatible with the Higgs boson predicted by the Standard Model paves the way for looking for DM with novel methods. An overview of the searches looking for a hidden sector in exotic Higgs decays and for invisible decays of the Higgs boson within the ATLAS experiment is presented. Prospects for searches with Large Hadron Collider data at a center-of-mass energy of 13 TeV are summarized.