Decaying dark matter: simulations and weak-lensing forecast

Despite evidence for the existence of dark matter (DM) from very high and low redshifts, a moderate amount of DM particle decay remains a valid possibility. This includes both models with very long-lived yet unstable particles or mixed scenarios where only a small fraction of dark matter is allowed to decay. In this paper, we investigate how DM particles decaying into radiation affect non-linear structure formation. We look at the power spectrum and its redshift evolution, varying both the decay lifetime (T) and the fraction of decaying -to-total dark matter (f ), and we propose a fitting function that reaches sub-percent precision below k similar to 10 h/Mpc. Based on this fit, we perform a forecast analysis for a Euclid-like weak lensing (WL) survey, including both massive neutrino and baryonic feedback parameters. We find that with WL observations alone, it is possible to rule out decay lifetimes smaller than T = 75 Gyr (at 95 percent CL) for the case that all DM is unstable. This constraint improves to T = 182 Gyr if the WL data is combined with CMB priors from the Planck satellite and to T = 275 Gyr if we further assume baryonic feedback to be fully constrained by upcoming Sunyaev-Zeldovich or X-ray data. The latter shows a factor of 3.2 improvement compared to constraints from CMB data alone. Regarding the scenario of a strongly decaying sub-component of dark matter with T similar to 30 Gyr or lower, it will be possible to rule out a decaying-to-total fraction of f > 0.49, f > 0.21, and f > 0.13 (at the 95 percent CL) for the same three scenarios. We conclude that the upcoming stage-IV WL surveys will allow us to significantly improve current constraints on the stability of the dark matter sector.

Automated summary

The study investigates the impact of dark matter particle decay on non-linear structure formation and uses Euclid-like weak lensing survey data to constrain the stability of the dark matter sector. The results show that upcoming stage-IV WL surveys will significantly improve current constraints on the stability of dark matter.