Cascade events at IceCube + DeepCore as a definitive constraint on the dark matter interpretation of the PAMELA and Fermi anomalies

Dark matter decaying or annihilating into μ+μ- or τ+τ- has been proposed as an explanation for the e± anomalies reported by PAMELA and Fermi. Recent analyses show that IceCube, supplemented by DeepCore, will be able to significantly constrain the parameter space of decays to μ+μ-, and rule out decays to τ+τ- and annihilations to μ+μ- in less than five years of running. These analyses rely on measuring tracklike events in IceCube + DeepCore from down-going νμ. In this paper we show that by instead measuring cascade events, which are induced by all neutrino flavors, IceCube + DeepCore can rule out decays to μ+μ- in only three years of running, and rule out decays to τ+τ- and annihilation to μ+μ- in only one year of running. These constraints are highly robust to the choice of dark matter halo profile and independent of dark matter-nucleon crosssection.