Time for PhD thesis defenses at the Oskar Klein Center

This spring there have been several PhD theses defenses here at the Oskar Klein Center, and as much as we hate saying good bye to some of our best students, we are proud to have been part of their professional lives.
The first to go was Jakob Nordin who defended his thesis with the title “Spectral Properties of Type Ia Supernovae and Implications for Cosmology” the 27th May 2011. During his PhD under the guidance of Professor Ariel Goobar, Jakob collected spectroscopic data of Type Ia supernovae with the purpose to study if SNIa are indeed good “standard candles” over a wide redshift range, a necessary condition to use these explosions to study the properties of dark energy. He has also investigated the nature of one of the color-brightness relation, one of the largest astrophysical corrections in the use of SNIa to measure distances. Finally, he has written a Monte-Carlo simulation package to investigate how systematic uncertainties in the use of Type Ia SNe as distance indicators propagate into our cosmological fits of dark energy parameters. Jakob is now ready to move on with a postdoc at the Berkeley, and we really wish him good luck with his life in California!

Another of Ariel Goobar students, Teresa Riehm also student at the Astronomy department, defended her thesis “Investigating the Dark Universe through Gravitational Lensing”. Teresa explored the effect of bending of light in the presence of matter to study the dark Universe, primarily dark matter, at different physical scales. From the smallest: microlensing by compact objects to the largest: strong lensing by the most massive galaxy clusters. Lensing by galaxy clusters also offer means to study parts of the universe otherwise too faint to be observed with current man made telescopes. In particular, Teresa has been investigating the feasibility to discover high-redshift supernovae lensed (magnified) by foreground clusters.

Sara Rydbeck defended her thesis on June 1st with Laura Covi from University of Göttingen as opponent. Sara, under the supervision of Joakim Edsjö, has focused on two themes, the first being modified gravity as an alternative to dark energy and if observations can distinguish between these two scenarios. For the second part of her thesis she has focused on searches for new physics at the LHC, and studied discovery potentials for supersymmetric models and the inert Higgs model. Hence her thesis has really been in the field of cosmoparticle physics covering both cosmology and particle physics. In the fall she starts as a postdoc at DESY, where she will have plenty of opportunities to expand in this field.

Life in Stockholm keeps going on as we get to Yashar Akrami, another of Joakim Edsjö student, who defended his thesis on June 7 with Roberto Trotta from Imperial College as opponent. Yashar has focused on comparing supersymmetric models with various observations and the problems that arise when investigating the often complex parameter spaces of the supersymmetric models. Hence he has focused on various statistical issues and scanning problems. In August he starts as a postdoc at University of Oslo, where he will move more into the field of cosmology.

Last but not least, Henrik Johansson who defended his thesis with the title Searching for an Ultra High-Energy Diffuse Flux of Extraterrestrial Neutrinos with IceCube 40″ on june 8, opponent Antoine Letessier-Selvon from Paris. Henrik has been working with the IceCube neutrino telescope at the South Pole. The Icecube detector was finalized last December and occupies a cubic kilometre in the glacier. Henriks work is based on an analysis when IceCube was 50% completed. Henrik thesis theme has been a search for high energy extraterrestrial flux of neutrinos. Being based in Stockholm under the supervision of Christian Walck, Henrik also had longer visits with collegues in Chiba, Japan and in Madison, USA from which he benefited a lot in his work.
In the analysis he pioneered the use of the optical module’s fast ADC, which records the signal for a longer time than the standard digitizer. At the end he put the most stringent limits obtained sofar for the flux of high energy neutrinos.

We wish all of them all the best for their future!

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