Why did you choose the OKC for doing a postdoc?
The broad focus on cosmology, with an emphasis on interaction between different areas, was very appealing. In addition, I had started working on capture of dark matter in stars and there is a lot of expertise in that area here in Stockholm (particularly Joakim Edsjö).
When I was given the offer, I was at a conference in Michigan with four OKC people in attendance (Marcus Berg and Joakim Edsjö plus PhD students Erik Lundström and Sara Rydbeck). That gave me a chance to see what the group was like and it made the decision an easy one.
What is your field of research?
My field of research is in the phenomenology of detecting dark matter, both directly and indirectly. The former case (direct detection) involves looking for interactions (scattering) of dark matter particles inside a detector, while the latter case (indirect detection) involves looking for products of dark matter particles that annihilate elsewhere.
Direct detection has long been a focus of my research and I continue to work in that area here at the OKC. I look at how various issues affect the signals seen in direct detection experiments, which might explain the apparent incompatibility between experiments that observe signals consistent with dark matter (CoGeNT, CRESST, and DAMA) and those that do not (CDMS and XENON, to name a few). The issues include how dark matter couples to ordinary matter, how the dark matter is distributed in the galaxy, and potential systematic issues in the experiments themselves (often involving energy calibrations). In addition, several of us (Yashar Akrami, Pat Scott, Jan Conrad, Joakim Edsjö and I) are looking at how direct detection results constrain supersymmetric models, which provide a natural candidate for a dark matter particle (the neutralino).
Another focus of my research is looking at dark matter capture in stars, where dark matter particles from the galactic halo passing through the star can scatter off of ordinary matter in the star and lose enough energy to become gravitationally bound. Subsequent scatters cause this dark matter to fall to the center of the star, where they can annihilate with each other. In the case of the Sun, those annihilations produce neutrinos that can be detected in neutrino observatories on Earth, such as IceCube. Some of us more theoretical types (Joakim Edsjö, Pat Scott and I) are working with the IceCube collaboration (notably the local members Matthias Danninger and Klas Hultqvist) on using IceCube results to constraint supersymmetric models via this capture/annihilation mechanism in the Sun.
Though I never expected to work in this area when coming to the OKC, I have occasionally worked with cosmic rays signals from dark matter annihilation in the halo. I have just recently begun working with others in the OKC (Joakim Edsjö, Natallia Karpenka, Antje Putze, and Pat Scott) on a project looking at antideuterons produced in these annihilations. I am really enjoying learning a new area of astrophysics on my first cosmic ray project.
What do you find unique for your field of research about the OKC?
The broad coverage of cosmology research and the emphasis on interaction is something not found in many places. My involvement with IceCube and cosmic ray research arose because of this interaction with experimental groups and other cosmologists. The supersymmetry global fits work, where multiple types of searches (accelerators and direct/indirect detection of dark matter) are combined to constrain supersymmetric models, is becoming a major area of research here for many OKC members. The OKC has been instrumental in bringing together people from many research groups in order to make such analyses happen.
What is your story before joining the OKC?
I am from the U.S. and mainly grew up in the state of Minnesota, a place that has a lot of similarities to Sweden (including the climate). Scandinavian immigration has had a significant impact on the local culture there (over 1.5 million Minnesotans have some Scandinavian background), more so than I knew until I came here to Stockholm, and I did not experience any culture shock in my first position outside the U.S.
My graduate studies started off at the University of California — Santa Barbara, where I intended to study string theory. During my first year there, I took a summer job on the CDMS dark matter experiment (under Harry Nelson). I had hardly heard of dark matter before taking that job, but I quickly fell in love with the topic and haven’t looked back since. That summer job turned into a two year stint on CDMS, but I eventually transferred to Michigan to get back into the theoretical side. I completed my PhD at Michigan under Katie Freese. I returned to Minnesota for a post-doc under Keith Olive at the Fine Theoretical Physics Institute.