Testing extensions to LCDM on small scales with forthcoming cosmic shear surveys

TL;DR

This paper assesses how upcoming Stage-IV weak lensing surveys can constrain small-scale extensions to the LCDM model, including warm dark matter, self-interacting dark matter, and spectral index running, using high-resolution simulations and synthetic observations.

Contribution

It introduces a detailed analysis of the constraining power of future surveys on small-scale dark matter models and spectral features, with new insights into cross-spectrum errors.

Findings

Stage-IV surveys can rule out WDM models with particle mass < 0.5 keV.

They can exclude SIDM models with cross-section > 10 cm^2 g^-1.

Strong constraints on cosmologies with a running spectral index are achievable.

Abstract

We investigate the constraining power of forthcoming Stage-IV weak lensing surveys (Euclid, LSST, and NGRST) for extensions to the LCDM model on small scales, via their impact on the cosmic shear power spectrum. We use high-resolution cosmological simulations to calculate how warm dark matter (WDM), self-interacting dark matter (SIDM) and a running of the spectral index affect the non-linear matter power spectrum, P(k), as a function of scale and redshift. We evaluate the cosmological constraining power using synthetic weak lensing observations derived from these power spectra and that take into account the anticipated source densities, shape noise and cosmic variance errors of upcoming surveys. We show that upcoming Stage-IV surveys will be able to place useful, independent constraints on both WDM models (ruling out models with a particle mass of < 0.5 keV) and SIDM models (ruling out models with a velocity-independent cross-section of > 10 cm^2 g^-1) through their effects on the small-scale cosmic shear power spectrum. Similarly, they will be able to strongly constrain cosmologies with a running spectral index. Finally, we explore the error associated with the cosmic shear cross-spectrum between tomographic bins, finding that it can be significantly affected by Poisson noise (the standard assumption is that the Poisson noise cancels between tomographic bins). We provide a new analytic form for the error on the cross-spectrum which accurately captures this effect.