Cosmic Shear in Effective Field Theory at Two-Loop Order: Revisiting $S_8$ in Dark Energy Survey Data

TL;DR

This paper applies two-loop effective field theory to analyze DES-Y3 cosmic shear data, providing precise constraints on $S_8$ and demonstrating the method's potential for testing new physics in upcoming surveys.

Contribution

First consistent two-loop EFT analysis of cosmic shear data, improving understanding of small-scale effects and intrinsic alignments, and offering competitive cosmological parameter constraints.

Findings

Measured $S_8$ consistent with previous results.

Demonstrated EFT's perturbative validity for cosmic shear.

Showed no $S_8$ tension in dynamical dark energy models.

Abstract

Cosmic shear is a powerful probe of cosmological distances, matter abundance and clustering in the low-redshift Universe. Cosmological parameter extraction from cosmic shear data is limited by our understanding of baryonic astrophysics, which severely restricts the range of scales used in such analyses. We show that the remaining scales are largely perturbative and can be accurately described with two-loop effective field theory (EFT) predictions. We present the first consistent analysis of the public cosmic shear data from the DES-Y3 catalogs in EFT at the two-loop order, renormalizing small-scale sensitivity in cosmic-shear predictions via a lensing-counterterm expansion and accounting for the intrinsic alignments of galaxies with spin-2 EFT predictions. We constrain the lensing amplitude competitively with standard (empirically-modeled) methods, finding $S_8 = 0.783^{+0.038}_{-0.031}$ ($S_8 = 0.802^{+0.031}_{-0.026}$ with BAO). The perturbativity of cosmic shear suggests novel opportunities for testing new physics with ongoing and upcoming cosmic shear experiments like Roman, Euclid, and LSST. As an example, we derive matter clustering constraints within the dynamical dark energy model from a combination of our DES-EFT cosmic shear likelihood, early-universe CMB priors, DESI BAO, and supernovae data, finding $S_8 = 0.824\pm 0.029$, indicating no $S_8$ tension in the growth of cosmic structure regardless of the underlying cosmological model and expansion history.