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

Dark matter decaying or annihilating into mu(+)mu(-) or tau(+)tau(-) 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 mu(+)mu(-), and rule out decays to tau(+)tau(-) and annihilations to mu(+)mu(-) in less than five years of running. These analyses rely on measuring tracklike events in IceCube + DeepCore from down-going nu(mu). 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 mu(+)mu(-) in only three years of running, and rule out decays to tau(+)tau(-) and annihilation to mu(+)mu(-) 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.