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 $v_k$, inducing a free-streaming suppression of matter fluctuations. This suppression can 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 $\ell <300$), surveys like Euclid or the Large Synoptic Survey Telescope can be sensitive to $v_k\gtrsim 90\mathrm{km}/\mathrm{s}$ for lifetimes $\tau \sim 1–5\mathrm{Gyr}$. 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 $\ell <3000$, we find that imaging surveys can be sensitive to $v_k\sim 10\mathrm{km}/\mathrm{s}$ for lifetimes $\tau \lesssim 10\mathrm{Gyr}$. Lensing will provide a particularly interesting complement to existing constraints in that they will probe the long lifetime regime ($\tau \gg H_0^{-1}$) 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.

• Received 11 January 2012

DOI:https://doi.org/10.1103/PhysRevD.85.043514