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Astrophysics, Relativity, and Cosmology Seminar - Charuhas Shiveshwarkar (Ohio State U) "Local Primordial Non-Gaussianity from Galaxy Surveys : Opportunities and Challenges"

Speaker:	(sign-up) Charuhas Shiveshwarkar (Ohio State U)
Date:	2/25/2026
Time:	11 a.m.
Location:	Rhondale Tso Seminar Room, Loomis 236
Event Contact:	Deanna Frye ddebord@illinois.edu
Sponsor:	Department of Physics
Event Type:	Seminar/Symposium
	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.