While the excess in cosmic-ray electrons and positrons reported by PAMELA and Fermi may be explained by dark matter decaying primarily into charged leptons, this does not necessarily mean that dark matter should not have any hadronic decay modes. In order to quantify the allowed hadronic activities, we derive constraints on the decay rates of dark matter into W W , ZZ, hh, qq and gg using the Fermi and HESS gamma-ray data. We also derive gamma-ray constraints on the leptonic e + e − , µ + µ − and τ + τ − final states. We find that dark matter must decay primarily into µ + µ − or τ + τ − in order to simultaneously explain the reported excess and meet all gamma-ray constraints.

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 track-like events in IceCube+DeepCore from down-going ν µ . 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 cross section.arXiv:0911.5188v4 [hep-ph]

Top polarization is an important probe of new physics that couples to the top sector, and which may be discovered at the 14 TeV LHC. Taking the example of the MSSM, we argue that top polarization measurements can put a constraint on the soft supersymmetry breaking parameter A t . In light of the recent discovery of a Higgs-like boson of mass ∼ 125 GeV, a large A t is a prediction of many supersymmetric models. To this end, we develop a detector level analysis methodology for extracting polarization information from hadronic tops using boosted jet substructure. We show that with 100 fb −1 of data, left and right 600 GeV stops can be distinguished to 4σ, and 800 GeV stops can be distinguished to 3σ.

We calculate the Cherenkov radiation from an e + e − pair at small separations, as occurs shortly after a pair conversion. The radiation is reduced (compared to that from two independent particles) when the pair separation is smaller than the wavelength of the emitted light. We estimate the reduction in light in large electromagnetic showers, and discuss the implications for detectors that observe Cherenkov radiation from showers in the Earth's atmosphere, as well as in oceans and Antarctic ice.