<p> In this work, we consider two different models of dark matter and set limits on results of experiments. One is a dynamic dark matter scenario where we put limits on parameters observable by experiments DAMA and XMASS through nuclear recoil of detector atoms (direct detection). The second is a case of dark matter annihilation into positrons and electrons and the signal this would produce on measured values of positron flux and ratio of electron to positron (indirect detection). The values of these quantities as measured by FERMI and PAMELA experiments are observed and an explanation using a dark matter annihilation is presented vs astrophysical sources of particles. </p><p> We explore a dynamic dark matter scenario with an ensemble of dark matter particles that starts at <i>m</i>₀ and spans a comb of particles separated by <i>j</i>^&delta;&Delta;<i> m</i>. We verify the model by using &Delta;<i>m</i> = &infin; and comparing the predictions to a non dynamic model for the same mass <i> m</i>0. We then observe the wider set of possibilities available with the dynamic dark matter model compared with the single mass case vis a vis constraints set by <i>NaI</i> and <i>Xe</i> detectors published by the DAMA and XMASS collaborations and check for validity of model against these measurements. </p><p> The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [&fcy;e+/(&fcy;e⁺+e^&minus;)], and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to e⁺ and e^&minus; final states. In this article, we calculate the signature &ldquo;bumps&rdquo; in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section <i>&sigma;v</i> &sim; 10^&minus;26 cm³/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than &sim;40 GeV.</p><p>

<p> The high-energy universe is known to be violent. Ultra High Energy Cosmic Rays (UHECRs) have been observed with kinetic energies exceeding 10²⁰ eV. Their origin, despite decades of observations, remains elusive. A unique probe of the sources and production mechanisms of these high energy cosmic rays can be neutrinos, since they are inevitably produced when high-energy protons interact. The IceCube Neutrino Observatory, located at the geographical South Pole in Antarctica, continuously monitors a total volume of 1 km³ of clear Antarctic ice for neutrino interactions. For this purpose, a total of 5160 optical sensors (photomultiplier tubes) have been melted deep into the glacier at depths between 1450m and 2450m. In 2013 IceCube reported one of its biggest discoveries, the observation of highly energetic neutrinos that are consistent with a possible extra-galactic origin. </p><p> In this dissertation we use IceCube data (recorded from 2012 to 2015) to study the spectral properties of this astrophysical neutrino flux with focus on electron and tau neutrino flavors. We developed a new neutrino identification and muon background rejection method using state-of-the-art machine-learning techniques, more specifically multi-class gradient boosted decision trees. In addition to enlarging the number of detected neutrino events (>10x increase over previous works), we lowered the energy threshold to below 1 TeV and thereby greatly improved upon the control and treatment of systematic uncertainties. The sample contains ~400 astrophysical electron and tau neutrinos, which increases the significance of the original discovery to beyond 8 standard deviations. We find the astrophysical neutrino flux to be well described by a single power-law consistent with expectations from Fermi-type acceleration of high-energy particles at astrophysical sources and obtain leading constraints on its properties. We further studied the possibility of additional spectral complexity, which significantly increases measurement uncertainties. No evidence for such scenarios was found. Finally we searched for a contribution from atmospheric neutrinos related to heavy meson (charm) decay in Earth's atmosphere and derive a flux upper limit of 4.8 times the benchmark pQCD flux prediction at 90% confidence level, dominated by systematic uncertainties, especially related to photon transport in the glacial ice.</p><p>