The standard model of Big Bang cosmology is the ΛCDM model, which incorporates cold dark matter and dark energy, two mysterious components of what is known as the “dark sector” of the universe, or sector not directly observable with light. Observations of primordial light in the universe allow precision tests of cosmological models, including the expansion rate of the universe, also known as the Hubble constant. Values of the Hubble constant determined using observations of primordial light and the ΛCDM model are in disagreement with the value determined from local observables, such as the recession velocities of galaxies observable with satellites. This tension may indicate a need to move beyond standard ΛCDM. During my International Research Opportunities Program (IROP) research at the Indian Institute of Astrophysics in Bangalore, India, I studied a possible extension of the ΛCDM model in which cold dark matter decays into dark radiation. In this project I investigated the effects of decaying dark matter on cosmological observables such as the Hubble constant. My results show that the decaying dark matter model may help alleviate tension between the indirect and direct determinations of the Hubble constant.