Effects of Unstable Dark Matter on Large-Scale Structure and Constraints from Future Surveys

TL;DR

This paper investigates how decaying dark matter affects large-scale structure and how future galaxy imaging surveys can constrain dark matter decay properties through weak lensing measurements.

Contribution

It develops a model to forecast constraints on decaying dark matter parameters using weak lensing data from upcoming surveys, including nonlinear corrections.

Findings

Surveys like Euclid and LSST can detect recoil velocities > 90 km/s for dark matter lifetimes of 1-5 Gyr.

Using nonlinear modeling, constraints could reach recoil velocities as low as 10 km/s for lifetimes under 10 Gyr.

Weak lensing provides a promising method to probe long-lived dark matter decay regimes.

Abstract

In this paper we explore the effect of decaying dark matter (DDM) on large-scale structure and possible constraints from galaxy imaging surveys. DDM models have been studied, in part, as a way to address apparent discrepancies between the predictions of standard cold dark matter models and observations of galactic structure. Our study is aimed at developing independent constraints on these models. In such models, DDM decays into a less massive, stable dark matter (SDM) particle and a significantly lighter particle. The small mass splitting between the parent DDM and the daughter SDM provides the SDM with a recoil or "kick" velocity vk, inducing a free-streaming suppression of matter fluctuations. This suppression may be probed via weak lensing power spectra measured by a number of forthcoming imaging surveys that aim primarily to constrain dark energy. Using scales on which linear perturbation theory alone is valid (multipoles < 300), surveys like Euclid or LSST can be sensitive to vk > 90 km/s for lifetimes ~ 1-5 Gyr. To estimate more aggressive constraints, we model nonlinear corrections to lensing power using a simple halo evolution model that is in good agreement with numerical simulations. In our most ambitious forecasts, using multipoles < 3000, we find that imaging surveys can be sensitive to vk ~ 10 km/s for lifetimes < 10 Gyr. Lensing will provide a particularly interesting complement to existing constraints in that they will probe the long lifetime regime far better than contemporary techniques. A caveat to these ambitious forecasts is that the evolution of perturbations on nonlinear scales will need to be well calibrated by numerical simulations before they can be realized. This work motivates the pursuit of such a numerical simulation campaign to constrain dark matter with cosmological weak lensing.