Physics with Large Scale Structure

The Universe at very large scales (much bigger than a galaxy) appears to show a very intricate structure known as Large Scale Structure (LSS). We have observed LSS through galaxies and black holes in them, covering very large volumes. During the 1970s when the standard model of Cosmology (i.e LCDM-GR) was coming together, a number of subtle and interesting physical effects were predicted. Two of the important effects were the existence of a special scale called Baryon Acoustic Oscillation (BAO-scale) and a special anisotropic pattern: the Redshift Space Distortions (RSD). These signatures were predicted to be seen in the matter distribution of the universe including in the structure traced by galaxies and black holes. Both of these predictions have been observed and are now used to answer some of the most interesting questions such as the geometry of space-time, the amount of dark matter, and the nature of dark energy. These along with other aspects of statistics of LSS can also provide the very first measurement of neutrino mass in coming years and sub-percent tests of General Relativity. At the same time, the LSS is also sensitive to details of how black-hole interacts with its surrounding matter and plays an important role in the properties of galaxies and larger structures around them. I will describe the rich physics behind these predictions and how they are used to push our understanding of the physical laws governing the evolution of our Universe. I will illustrate how the ongoing largest-ever galaxy redshift experiment called Dark Energy Spectroscopic Instrument (DESI) is going to change the theory land-scape of gravity and dark energy models and measure neutrino masses.