From pixels to cosmology: exploring the universe through optical transient survey science with DES and LSST

The Legacy Survey of Space and Time (LSST) will soon start operations, marking an enormous boost in our optical transient discovery rate. The Vera Rubin Observatory will scan the southern sky approximately once every 3 nights, and will observe ∼10^6 varying sources each night. Optical transient phenomena in the extragalactic realm not only reveal individual event astrophysics but also provide insight into the properties of the universe we inhabit. By utilizing standardizable candles like Type Ia Supernovae, we can study the redshift-distance relationship, known as the Hubble Diagram, and uncover the accelerated expansion of the universe. Accurate measurements of the expansion history of our universe and current expansion rate can help us constrain the current standard cosmological model parameters, and even more, contrast its prediction power against the numerous alternative models. Whilst LSST is still in construction, the Dark Energy Survey (DES) is about to make public the largest collection of supernova light-curves measured with a single instrument to this date. In this talk I will present results on the application of forward modelling photometry techniques for measuring the final DES Y5 SNIa cosmological sample, as well as the characterization and current development of the LSST transient discovery pipeline, and provide an end-to-end assessment of the impact of its performance in the inference of cosmological parameters using the Dark Energy Science Collaboration (DESC) LSST data challenge simulation (DC2).