Weak-scale supersymmetry is one of the most favoured theories beyond the Standard Model of particle physics that elegantly solves various theoretical and observational problems in both particle physics and cosmology. In this thesis, I describe the theoretical foundations of supersymmetry, issues that it can address and concrete supersymmetric models that are widely used in phenomenological studies. I discuss how the predictions of supersymmetric models may be compared with observational data from both colliders and cosmology. I show why constraints on supersymmetric parameters by direct and indirect searches of particle dark matter are of particular interest in this respect. Gamma-ray observations of astrophysical sources, in particular dwarf spheroidal galaxies, by the Fermi satellite, and recording nuclear recoil events and energies by future ton-scale direct detection experiments are shown to provide powerful tools in searches for supersymmetric dark matter and estimating supersymmetric parameters. I discuss some major statistical issues in supersymmetric global fits to experimental data. In particular, I further demonstrate that existing advanced scanning techniques may fail in correctly mapping the statistical properties of the parameter spaces even for the simplest supersymmetric models. Complementary scanning methods based on Genetic Algorithms are proposed. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

While the dark matter has so far only revealed itself through the gravitational influence it exerts on its surroundings, there are good reasons to believe it is made up by WIMPs – a hypothetical class of heavy elementary particles not encompassed by the Standard Model of particle physics. The Inert Doublet Model constitutes a simple extension of the Standard Model Higgs sector. The model provides a new set of scalar particles, denoted inert scalars because of their lack of direct coupling to matter, of which the lightest is a WIMP dark matter candidate. Another popular Standard Model extension is that of supersymmetry. In the most minimal scenario the particle content is roughly doubled, and the lightest of the new supersymmetric particles, which typically is a neutralino, is a WIMP dark matter candidate. In this thesis the phenomenology of inert scalar and supersymmetric dark matter is studied. Relic density calculations are performed, and experimental signatures in indirect detection experiments and accelerator searches are derived. The Inert Doublet Model shows promising prospects for indirect detection of dark matter annihilations into monochromatic photons. It is also constrained by the old LEP II accelerator data. Some phenomenological differences between the Minimal Supersymmetric Standard Model and a slight extension, the Beyond the Minimal Supersymmetric Standard Model, can be found. Also, supersymmetric dark matter models can be detected already within the early LHC accelerator data.

Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate. One of the most interesting scenarios is the creation of monochromatic gamma-rays from the annihilation or decay of these particles. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. In this thesis, the search for spectral lines with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi) is presented. The satellite was successfully launched from Cape Canaveral in Florida, USA, on 11 June, 2008. The energy resolution and performance of the detector are both key factors in the search and are investigated here using beam test data, taken at CERN in 2006 with a scaled-down version of the Fermi-LAT instrument. A variety of statistical methods, based on both hypothesis tests and confidence interval calculations, are then reviewed and tested in terms of their statistical power and coverage. A selection of the statistical methods are further developed into peak finding algorithms and applied to a simulated data set called obssim2, which corresponds to one year of observations with the Fermi-LAT instrument, and to almost one year of Fermi-LAT data in the energy range 20–300 GeV. The analysis on Fermi-LAT data yielded no detection of spectral lines, so limits are placed on the velocity-averaged cross-section, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%3C%5Csigma%20v%3E_%7B%5Cgamma%20X%7D" />, and the decay lifetime, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ctau_%7B%5Cgamma%20X%7D" />, and theoretical implications are discussed. / QC20100525 / GLAST

Gamma-ray bursts (GRBs) are the most energetic electromagnetic events in the universe, but there are still unanswered questions about them, like the underlying radiation mechanisms that cause the different parts of their light curves. Given that Wolf-Rayet (WR) stars with circumburst rings could be the progenitor of GRBs with late flares \cite{complex}, the purpose of this thesis was to determine if the precursor and the main emission of GRBs with late time flares might originate due to different radiation mechanisms, and thereby if WR stars could be the progenitors. 271 of the longest GRBs with flux above 10 photons/cm$^2$/s were studied and all GRBs with a precursor and a defined quiescent period were chosen for further studies. The chosen 39 GRBs were divided into different categories depending on the appearance of their light curves. A gold sample with $R_{P, max}/R_{D, max} &lt; 0.4$ and $T_Q/T_{tot} &gt; 0.5$, for the maximum count rate of the precursor $R_{P, max}$, the dominant emission $R_{D, max}$, and for the normalised quiescent period $T_Q/T_{tot}$ was concluded to have similar characteristics and to fit what would be expected if WR stars would be the progenitors. This group of GRBs all have a short and less bright precursor, a long quiescent period and a main emission which is brighter and longer than the precursor. The distributions of the photon index $\alpha$ for the precursor and the dominant emission for the gold sample indicate that the precursor is due to photospheric emission and the dominant emission is due to synchrotron emission. This is consistent with the interpretation that the precursor is a result of the jet interacting with the photosphere and the dominant emission is a result of interactions with the circumburst ring of a star like the WR stars. The next step in this investigation would be to study GRBs with more than one precursor that otherwise fit the description of the gold sample, to determine if these fit into the gold sample as well. / Gammablixtrar (GRB) är de mest kraftfulla elektromagnetiska eventen i universum men det finns fortfarande obesvarade frågor om dem, som de underliggande strålningsmekanismerna som orsakar de olika delarna av deras ljuskurvor. För en del av alla GRBs tar det upp till eller mer än 100 sekunder från utlösningstiden till det att en topp ses i ljuskurvan. För dessa finns då ofta en liten svag topp, som följs av en lång lugn period och sedan den dominant, starkare utstrålningen. GRBs tros kunna härstamma från Wolf-Rayet-stjärnor (WR-stjärnor), som är massiva, döende stjärnor som kan vara omringade av bubblor, nebulosor, och ringar. Om GRBs härstammar från dessa förväntas den första mindre toppen och den andra större toppen uppkomma på grund av olika strålningsprocesser. Syftet med detta projekt var därför att undersöka huruvida dessa toppar uppkommer på grund av olika processer eller ej. Sammanfattningsvis så hittades en distinkt och homogen grupp av GRBs med likande egenskaper. Resultaten påvisar att den första svaga toppen är fotosfärisk strålning, så att den uppkommer på grund av att jetstrålen från GRBn interagerar med fotosfären. Därtill tyder resultaten på att den dominanta starkare toppen är synkrotronstrålning, som kan uppkomma när jetstrålen interagerar med en ring runt en WR-stjärna. Nästa steg i detta projekt skulle vara att studera GRBs med fler än en mindre topp innan den dominant utstrålningen, för att se om dessa också har liknande egenskaper som de som hittades i den homogena gruppen.

This thesis addresses the isotropic diffuse gamma-ray background, as measured by the Fermi gamma ray space telescope, and its implications for indirect detection of dark matter. We describe the measurement of the isotropic background, including also an alternative analysis method besides the one published by the Fermi-LAT collaboration. The measured isotropic diffuse background is compatible with a power law differential energy spectrum with a spectral index of  -2.41 ± 0.05 and -2.39 ± 0.08, for the two analysis methods respectively. This is a softer spectrum than previously reported by the EGRET experiment. This rules out any dominant contribution with a significantly different shape, e.g. from dark matter, in the energy range 20 MeV to 102.4 GeV. Instead we present upper limits on a signal originating from annihilating dark matter of extragalactic origin. The uncertainty in the dark matter signal is primarily dependent on the cosmological evolution of the dark matter distribution. We use recent N-body simulations of structure formation, as well as a semi-analytical calculation, to assess this uncertainty. We investigate three main annihilation channels and find that in some, but not in all, of our scenarios we can start to probe, and sometimes rule out, interesting parameter spaces of particle physics models beyond the standard model.We also investigate the possibility to use the angular anisotropies of the annihilation signal to separate it from a background originating from conventional sources, e.g. from active galactic nuclei. By carefully modelling the performance of the Fermi gamma-ray space telescope and galactic foregrounds we find that this method could be as sensitive as using information from the energy spectrum only. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript.</p>

Gamma-ray burst light curves are notoriously irregular, yet a significant number consists of a single fast-rising, exponentially decaying pulse. These are called single-peaked light curves. The goal of this thesis is to analyse a sample of 2710 GRBs collected by the Fermi space telescope by identifying single-peaked bursts and comparing their properties to those of the multi-peaked bursts. Furthermore, the validity of the relativistic shock breakout theory as an explanation for single-peaked, low-luminosity GRBs is investigated using a closure relation. For this investigation, the Fermi sample wascomplemented by low-luminosity GRBs observed by other instruments. A criterion for selecting single-peaked bursts was successfully developed, yielding 48% long and 79% short, single-peaked GRBs. Significant differences between the populations were found in multiple properties. In general, single-peaked GRBs appear to be weaker and more slowly varying than multi-peaked ones; however, a larger sample of GRBs with redshift measurements is needed to draw conclusions about possible intrinsic differences in energy connected to the progenitor systems. The investigation of low-luminosity GRBs’ compliance with the shock breakout closure relation showed that 64% of the low-luminosity GRBs were within a factor 5 of fulfilling the relation as opposed to only 24% of high-luminosity GRBs. It was further shown that only a small number (&lt; 5%) of Fermi GRBs without redshift measurements could be low-luminosity shock breakout GRBs according to this theory. In conclusion, while the shock breakout closure relation does hold for a greater proportion of low-luminosity GRBs than high-luminosity GRBs, there is still a large number of low-luminosity GRBs left unexplained by this theory. / Gammablixtljuskurvor är ökänt oregelbundna men en betydande andel består av en enda snabbt stigande och exponentiellt avtagande puls. Dessa kallas singelpeakade ljuskurvor. Målet med detta examensarbete är att analysera de 2710 gammablixtar som Fermirymdteleskopet har observerat genom att identifiera singelpeakade blixtar och jämföra deras egenskaper med multipeakade blixtars. Dessutom undersöks den relativistiska shockbreakoutteorin som förklaringsmodell för singelpeakade lågluminositetsgammablixtar. I denna undersökning kompletterades fermiblixtarna med lågluminositetsblixtar från andra instrument. Ett kriterium för identifikation av singelpeakade gammablixtar utvecklades och detta resulterade i 48% långa och 70% korta, singelpeakade gammablixtar. Flertalet egenskaper uppvisade signifikanta skillnader mellan populationerna. I allmänhet verkar singelpeakade gammablixtar vara svagare och variera långsammare än multipeakade. Dock behövs en större population av gammablixtar med uppmätta rödskift för att med säkerhet kunna avgöra om singelpeakade blixtar verkligen släpper ut mindre energi. Undersökningen av huruvida lågluminositetsgammablixtar kan förklaras med shockbreakoutteorin visade att 64% av lågluminositetsblixtarna uppfyllde kravet upp till en faktor fem medan bara 24% av högluminositetsblixtarna gjorde det. Vidare visades att endast ett litet antal (&lt;5%) av fermiblixtarna utan uppmätta rödskift skulle kunna vara lågluminositetsshockbreakoutblixtar enligt denna teori. Även om shockbreakoutteorin kan förklara en större andel av lågluminositetsblixtarna än högluminositetsblixtarna återstår ett stort antal oförklarade lågluminositetsblixtar.