Dark matter particles in the form of supersymmetric Weakly Interacting Massive Particles (WIMPs) could accumulate in the centre of the Sun because of gravitational trapping. Pair-wise annihilations of WIMPs could create standard model particles out of which neutrinos could reach the Earth. Data from the IceCube 22-string neutrino telescope have been searched for signals from dark matter annihilations in the Sun. Highly sophisticated analysis methods have been developed to discern signal neutrinos from the severe background of atmospheric particle showers. No signal has been found in a dataset of 104 days livetime taken in 2007, and an upper limit has been placed on the muon flux in the South Pole ice induced by neutrinos from the Sun, reaching down to 330 km-2y-1. The flux limit has been converted into an upper limit on the neutralino scattering cross-section, which reaches down to 2.8*10-40 cm2 for spin-dependent interactions. / Four articles are appended to the thesis:I. G. Wikström for the IceCube collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 135.II. A. Gross, C. Ha, C. Rott, M. Tluczykont, E. Resconi, T. DeYoung and G. Wikström for the IceCube Collaboration, Proc. of the 30th ICRC,arXiv/0711.0353 [astro-ph] (2007) 11.III. G. Wikström and J. Edsjö, JCAP 04 (2009) 009.IV. R. Abbasi et al. (IceCube collaboration), accepted for publication in Phys. Rev. Lett., arXiv/0902.2460v3 [astro-ph.CO] (2009). / IceCube

The cubic-kilometer sized IceCube neutrino observatory, constructed in the glacial ice at the South Pole, searches indirectly for dark matter via neutrinos from dark matter self-annihilations. It has a high discovery potential through striking signatures. This thesis presents searches for dark matter annihilations in the center of the Sun using experimental data collected with IceCube. The main physics analysis described here was performed for dark matter in the form of weakly interacting massive particles (WIMPs) with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore sub-array was included in the analysis, lowering the energy threshold and extending the search to the austral summer. Data from 317 days live-time are consistent with the expected background from atmospheric muons and neutrinos. Upper limits were set on the dark matter annihilation rate, with conversions to limits on the WIMP-proton scattering cross section, which initiates the WIMP capture process in the Sun.These are the most stringent spin-dependent WIMP-proton cross-sections limits to date above 35 GeV for most WIMP models. In addition, a formalism for quickly and directly comparing event-level IceCube data with arbitrary annihilation spectra in detailed model scans, considering not only total event counts but also event directions and energy estimators, is presented. Two analyses were made that show an application of this formalism to both model exclusion and parameter estimation in models of supersymmetry. An analysis was also conducted that extended for the first time indirect dark matter searches with neutrinos using IceCube data, to an alternative dark matter candidate, Kaluza-Klein particles, arising from theories with extra space-time dimensions. The methods developed for the solar dark matter search were applied to look for neutrino emission during a flare of the Crab Nebula in 2010.

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In this work the search for the dark matter arising from a model of extra dimensions, otherwise known as Kaluza Klein WIMPs, on the data taken with the AMANDA neutrino telescope in the South Pole is presented. The limit on the dark matter from the Kaluza Klein Solar WIMPs analysis on the data taken from year 2001 to 2003 is derived.

A survey of the theory of neutrino oscillations in dense matter and neutrino backgrounds is presented. We discuss collective neutrino systems using the gyroscopic pendulum analogy and describe the motion that results from self-induced parametric resonances. The effects of dense matter on the flavour oscillations of neutrinos are also detailed. This theory is applied to the case of continuous supernova neutrino spectra and explanations of the spectral swapping behaviour seen in numerical studies are summarized. The results of numerical simulations of supernova oscillations in turbulent supernova backgrounds are presented and discussed. We study the motion of two example supernova neutrino spectra and examine the differences in the dynamics and flavour evolution that results from adding turbulent fluctuations to the supernova matter background. We also investigate the effect that fluctuations in the neutrino density can have on the oscillation behaviour. We find that in general the final neutrino spectra emerging from the inner supernova regions are quite robust to fluctuations in the backgrounds in our model, while the intermediate dynamics can be very strongly altered. Some significant changes in the final spectra are also found to occur when the neutrino background density fluctuations are large. We give a detailed review of the resonant matter effects that determine the survival probabilities of atmospheric muon neutrinos. The differences between various Earth density models are described, and these models are then used to predict the flux of muon-type neutrino events in the Deep Core extension to the IceCube detector. We use recent results from the detector collaboration and build on previous work which considered the sensitivity of the detector to the mass hierarchy, and show that uncertainties in the Earth's density can have a significant influence on the event rates.

The Minimally Supersymmetric Standard Model (MSSM) provides us with a WIMP dark matter candidate particle, the neutralino. Neutralinos from the dark matter halo can potentially become captured by the sun and concentrated in the core, where they can undergo self-annihilation and so produce a distinct neutrino signal. The IceCube Neutrino Observatory has the potential to detect this neutrino signal and thus give indirect evidence of the presence and properties of neutralino dark matter. Although the full, unconstrained MSSM has 105 parameters this can be reduced to 25 parameters by the application of physically motivated assumptions. Scans of this MSSM-25 parameter space are conducted using the DarkSUSY software package and an adaptive scanning technique based on the Monte-Carlo VEGAS algorithm. The IceCube exclusion confidence level is then calculated for a set of points produced by these scans. Results indicate that the detection capability of IceCube exceeds that of current direct detection methods in certain regions of the parameter space. The use of a 25 dimensional parameter space reveals that there are new regions of observables with high exclusion confidence levels compared to earlier simulations performed with a seven dimensional parameter space.

It is astonishing both how little and how much we know about neutrinos. On one hand, the neutrino is the second most abundant particle in our Universe. Neutrinos may be created in the Sun, core collapse supernovae, cosmic rays, geological background radiation, supernova remnants and in the Big Bang. On the other hand, they have unimaginably small masses and are unwilling to react with their surroundings. Because of their abundance and their inclination to show us physics beyond the standard model of particle physics, neutrinos are hoped to carry yet unknown information of the Universe. However, it will take some effort and time to persuade the neutrinos to tell us what they know. Among the things we do not yet know of the neutrinos, is the -phase in the neutrino mixing matrix. If is in fact non-zero, neutrino flavour oscillations violate CP-symmetry. Also, if neutrino masses are introduced in the standard model through the See-Saw mechanism and if leptogenesis is a valid theory, CP-violation in neutrino oscillations could help explain why our Universe has no antimatter even though equal amounts of matter and antimatter should have been created at the Big Bang. In this thesis, we investigate the flavour evolution of supernova neutrinos. We present the full Hamiltonian in the flavour basis for our system and identify how the different contributions affect the evolution and in which environment. We also present a theoretical motivation from [1, 2] as to how a non-zero -phase affects the flavour evolution and the final energy spectra. The analytical conclusion is that it has no impact under the assumptions made in our analysis. Thus, the -phase may not be measurable from supernova neutrinos.

The Radio Ice Cherenkov Experiment(RICE) located at the South Pole, is designed to detect the coherent broad-band radio Cherenkov radiation emitted when a high energy (10¹⁵ to 10¹⁸ eV) neutrino interacts with a nucleon in the ice. Observations have identified that Gamma Ray Bursts(GRBs) are possible sites for high energy neutrino production. We consider here GRBs which occurred in the years 2001 to 2005 inclusive during the operational times of RICE. Using GRB photon spectral data, we calculate the neutrino spectra predicted for these GRBs and the subsequent event number expected in RICE. We re-analyze RICE data in small time windows surrounding the GRB burst start times using a refined method involving by eye analysis of this reduced data set and find no neutrino events in the data set. Using the effective volume of RICE appropriate for each GRB we calculate neutrino flux limits for the GRBs. Although the flux limits are several orders of magnitude weaker than the expected flux, the RICE GRB neutrino limits are the only limits in the PeV to EeV energy range.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.