Unconventional dark matter models: a brief review

Although weakly interacting massive particle (WIMP) scenario is very well motivated, it is not guaranteed to be the truth. It is important to keep mind open and consider other well-motivated scenarios. In this paper, we briefly review several possible non-WIMP dark matter (DM) candidates. First, we discuss details on asymmetric DM models, in which the baryon asymmetry in standard model sector is related to the asymmetry in DM sector. We discuss how DM relic abundance is determined in such models. Also we cover the possible interesting experimental signatures induced by its asymmetric nature. Then we consider ultralight DM candidates, i.e., axion and dark photon. In such scenarios, DM should be treated as a coherently oscillating background, instead of each individual particle. Searching strategies for such DM candidates is very different than those in conventional DM models. We discuss several interesting experiments looking for these ultralight particles. We also cover interesting subtleties encountered in those experiments.