Zachary Slepian is originally from Fairfield, Connecticut. He received a BA summa cum laude from Princeton (2011), working with J. Richard Gott, III on his senior thesis, an MSt in philosophy of physics at Oxford (2012), and a PhD in Astrophysics (2016) from Harvard, advised by Daniel J. Eisenstein. During his PhD, he focused on Baryon Acoustic Oscillations (BAO) in the 2-point and 3-point correlation function (3PCF) of galaxies, constraining a possible systematic sourced by high-redshift baryon-dark matter relative velocities using the 3PCF. This entailed developing a transformatively fast 3PCF algorithm, enabling the first high-significance detection of BAO in the 3PCF and a measurement of the cosmic distance scale six billion years ago to percent precision. Post-PhD, he spent one year as a Chamberlain Fellow and one year as an Einstein Fellow at Lawrence Berkeley National Laboratory, where highlights included an implementation of the 3PCF algorithm capable of computing the 3PCF for the entire observable Universe in 20 hours on NERSC’s Cori supercomputer, application of the 3PCF to MHD turbulence, and novel analytic solutions for the Friedmann equation in the presence of neutrinos or warm dark matter. His current research follows three broad paths: creating theoretical models for large-scale structure, designing fast algorithms to measure it, and applying them to datasets such as BOSS, eBOSS, and DESI. Cutting across these areas are a strong attraction to analytic methods and excitement about effective use of high-performance computing. Zachary is currently an Assistant Professor at the University of Florida.
Talk Title and Abstract:
Exploring Fundamental Physics with Friends and Neighbors
In this talk I will outline both the underlying theory and novel methods being developed by my group to enable Dark Energy Spectroscopic Instrument (DESI; 30 M galaxy spectra, 2020-2025) to reveal the dark (energy) and the invisible (neutrino mass). Dark energy drives cosmic expansion, so measuring the Universe's expansion history constrains dark energy. The first and second parts of my talk will focus on novel standard rulers to make this measurement. I will begin with DESI's precursor, BOSS, and show how the first full measurement of correlations between triples of galaxies (the 3-point function) enabled detection of sound waves from the early Universe and their use to improve cosmic distance constraints. This is by way of motivation, to show what at minimum we can do with DESI, which is 30X as big as BOSS. I will then move to a more ambitious agenda being undertaken by my group: how can we use 3, 4, 5, and 6-point functions to maximize the leverage of DESI on dark energy? I will present preliminary measurements of these functions based on a transformative algorithm my group has developed, based on angular momentum decomposition tools drawn from particle physics. In the last part of my talk, I will move to neutrinos, whose mass can be measured from their imprint on galaxy clustering. I will present a simple, analytic picture of both the development of neutrinos' spatial distribution in the early Universe, and of their late-time effects on the matter. I will close with a novel neutrino signature in the galaxy 3-point function identified by my group which will increase DESI's likelihood of making the first actual measurement of the neutrino mass.
Would you like to join this Zoom seminar? Please email Donna Hayes.
Host