Dark matter, dark energy, and alternate models: A review

Abstract

The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the uni-verse is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM are clearly ruled out,there is still a plethora of viable particles that fit the bill. In the context of DE, while current observations favour a cosmological constantpicture, there are other competing models that are equally likely. This paper reviews the different possible candidates for DM includingexotic candidates and their possible detection. This review also covers the different models for DE and the possibility of unified modelsfor DM and DE. Keeping in mind the negative results in some of the ongoing DM detection experiments, here we also review the possiblealternatives to both DM and DE (such as MOND and modifications of general relativity) and possible means of observationally distin-guishing between the alternatives.