IUCAA Brochure 2024

Cosmology from Large-Scale Structure The physics of the early Universe predicts a distinct set of spatial correlations called baryon acoustic oscillations (BAO) that imprint on the large-scale distribution of galaxies in the Universe. The BAO feature shows up as a bump when measuring the pairwise number density of galaxies as a function of pair separation. The length scale at which the BAO feature occurs (typically of order 150Megaparsec at the present epoch) can act as a standard rod that can be used to constrain cosmological parameters. Measuring the precise value of this scale at different epochs of the Universe is one of the key science drivers of current and upcoming galaxy surveys. Typical analyses in this `BAO cosmology' programme assume that the underlying model of the Universe is well-approximated by the Lambda-cold dark matter (LCDM) framework. IUCAA researchers have developed an analysis technique that allows the BAO feature to be used in a model- independent manner, i.e., the same analysis is simultaneously applicable in constraining not only LCDM but also other classes of `modified gravity' or `dark energy' models. The new technique relies on basic physical aspects of cosmological structure formation shared by a wide class of models including and beyond LCDM, combined with a simple data-driven description of the BAO feature using polynomials which is embedded in a fully Bayesian analysis framework. The new technique thus opens the door to using the BAO feature to its full capacity as a probe of primordial Cosmology.