High-luminosity fixed target experiments provide impressive sensitivity to new light weakly coupled degrees of freedom. In the first part of this talk, I will discuss the minimal case of a scalar singlet S coupled to the Standard Model through the Higgs portal, that decays visibly to leptons for scalar masses below the dipion threshold. The dataset from the LSND experiment is found to impose the leading constraints within two mass windows between mS ∼ 100 and 350 MeV. In the second part of the talk, I will introduce potentially the world's most sensitive location to search for millicharged particles in the 10 MeV to 100 GeV mass range: the forward region at the LHC. I will show that the proposed scintillator-based experiment, FORward MicrOcharge SeArch (FORMOSA) in this location, can discover millicharged particles in a large and unexplored parameter space, and study strongly interacting dark matter that cannot be detected by ground-based direct-detection experiments. Furthermore, I will discuss some additional physics potential of FORMOSA, that not only provides leading sensitivity to MCPs but also is extremely sensitive to other forms of exotica beyond the standard model (BSM), such as heavy neutrinos and DM with a large electric dipole moment (EDM). This talk is based on arXiv:2004.14515 & arXiv:2010.07941.
