Abstract:  
The Universe is awash with tens-of-MeV neutrinos of all species coming from all past core-collapse supernovae, also known as the diffuse supernova neutrino background (DSNB). Detecting the DSNB would open up new avenues in multi-messenger astronomy. In particular, it offers the unique opportunity to probe properties of the cosmos using neutrinos, as opposed to photons. The Super-Kamiokande experiment, loaded with gadolinium, is expected to collect dozens of events from the DSNB in the next decade. Future detectors such as Hyper-Kamiokande and Theia will perform even better, collecting hundreds of events after a decade of data-taking. In this talk, I will discuss how a future detection of the DSNB can be used to inform various research topics in cosmology, astrophysics and particle physics, focusing on a few examples from each field. In particular, I will expand on how the DSNB can be used to infer measurements of the Hubble constant, as well as constrain various parameters of the cosmological star formation rate. On the particle physics side, the DSNB can be used to probe the neutrino lifetime and the possibility that neutrinos are pseudo-Dirac fermions.