Astrophysics, Relativity, and Cosmology Seminar - Charuhas Shiveshwarkar (Ohio State U) "Local Primordial Non-Gaussianity from Galaxy Surveys : Opportunities and Challenges"
Feb 25, 2026 11:00 am
Rhondale Tso Seminar Room, Loomis 236
- Sponsor
- Department of Physics
- Speaker
- Charuhas Shiveshwarkar (Ohio State U)
- Contact
- Deanna Frye
- ddebord@illinois.edu
- Views
- 60
- Originating Calendar
- Physics - Astrophysics, Relativity, and Cosmology Seminar
- Primordial non-Gaussianity (PnG) is a powerful, model-dependent probe of different cosmic inflation scenarios. In particular, \textit{local} Primordial non-Gaussianity (LPnG) is a distinguishing feature of cosmic inflation with at least one additional light degree of freedom beyond the inflaton. A robust detection of non-trivial LPnG would therefore significantly improve our understanding of the inflationary universe by ruling out all single-field models of inflation. Although state-of-the-art constraints on LPnG come from Cosmic Microwave Background (CMB) datasets, the next frontier in its detection lies in large-scale galaxy clustering surveys such as DESI, SPHEREx, and SpecS5. LPnG is particularly amenable to detection in such surveys due to its scale-dependent impact on the galaxy bias, which peaks at the largest scales. However, constraints on LPnG obtained from galaxy power spectra are potentially limited by near-horizon, non-primordial effects on galaxy clustering as well as by parameter degeneracies between the LPnG parameter $f_{NL}$ and galaxy bias parameters -- in particular, the degeneracy between $f_{NL}$ and the bias parameter $b_{\phi}$.In this talk, I will discuss theoretical challenges presented by late-time, non-primordial effects on large-scale galaxy clustering and present recent work using the Separate Universe framework to better understand the relationship between $b_{\phi}$
and halo/galaxy bias. This Separate Universe approach provides a unified theoretical perspective that connects bias parameters to halo formation history and selection effects, improving our ability to mitigate the $f_{NL}-b_{\phi}$ degeneracy and thereby increase the constraining power of the next generation of large-scale galaxy surveys.