In this thesis I present our recent work on gamma-ray searches for dark matter with the Fermi Large Area Telescope (Fermi-LAT). We have targeted dwarf spheroidal galaxies since they are very dark matter dominated systems, and we have developed a novel joint likelihood method to combine the observations of a set of targets. In the first iteration of the joint likelihood analysis, 10 dwarf spheroidal galaxies are targeted and 2 years of Fermi-LAT data is analyzed. The resulting upper limits on the dark matter annihilation cross-section range from about 10−26 cm3 s−1 for dark matter masses of 5 GeV to about 5 × 10−23 cm3 s−1 for dark matter masses of 1 TeV, depending on the annihilation channel. For the first time, dark matter models with a cross section above the canonical thermal relic cross section (∼ 3 × 10−26 cm3 s−1) are strongly disfavored by a gamma-ray experiment. In the second iteration we include 15 dwarf spheroidal galaxies in the combined analysis, employ 4 years of data and an improved calculation of the dark matter density. The obtained upper limits range from about 10−26 cm3 s−1 for dark matter masses of 2 GeV to about 10−21 cm3 s−1 for dark matter masses of 10 TeV, depending on the annihilation channel. I briefly describe some of the evidence for dark matter, the Fermi-LAT instrument and public data releases, dwarf spheroidal galaxies, likelihood analysis, and results from analyses of Fermi-LAT data. I also document some of the tests made to verify the method and to compare different analysis setups.

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Thesis (doctoral)--Göteborg University, 2008. / Includes bibliographical references.

Thesis (Ph.D.)--Kent State University, 2009. / Title from PDF t.p. (viewed April 9, 2010). Advisor: Michael Lee. Includes bibliographical references (p. 97-101).

Dresden, Techn. Univ., Diss., 2003.

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<p> A study of the Fermi surface of mercury has been carried out using cyclotron resonance and magnetoresistance techniques. Oscillations of the microwave surface impedance, which have been identified as quantum oscillations, have appeared at high magnetic field strengths, and a study of these oscillations has added more information about the Fermi surface. </p> <p> The results of these experiments are compared with two models of the Fermi surface, the nearly-free-electron model, and the relativistic-augmented-plane-wave model. The relativistic-augmented-plane-wave model was found to require only small modifications to be consistent with the data. </p> / Thesis / Doctor of Philosophy (PhD)

<p> Under certain conditions, an induced torque measurement is a measure of the ratio of the resistivity to the square of the Hall constant. Induced torque measurements can be directly related to the connectivity of the Fermi surface.</p> <p> A modulation technique for measuring induced torque is justifield theoretically, and an instrument employing this technique is characterized. Operational limitations on parameters such as sample resistivity and modulation rate are specified. A new procedure is proposed to extract more information from induced torque measurements. This procedure would allow the measurement of resistivity and Hall constant of ellipsoidal samples. The procedure is untested but appears to be feasible.</p> <p> Observations of the induced torque of Hg3-δAsF6 show that the Fermi surface supports an open orbit in one direction. This is discussed in the context of a model (Razavi et al., 1979), which has Fermi surface cylinders of common direction. This is based on conduction in Hg chain directions, which lie in only two directions. At magnetic fields greater than 3.0 Tesla, magnetic breakdown is observed. A Brillouin zone constructed using Hg chain symmetry and crystal parameters yields reciprocal lattice vectors compatible with the observed magnetic breakdown. The model is confirmed but a refinement is needed to allow an undulation of the Fermi surface cylinders.</p> / Thesis / Master of Science (MSc)

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