An intriguing fact, which has become ever more evident during the last years, is that the matter mass density in the Universe is by a factor of around five dominated by so-called dark matter. The nature of the dark matter particles is still largely unknown, except that that some properties are required by the fact that their effect is only so far shown by gravitational influence. For instance, the coupling to electromagnetism (i.e., to photons) and to the strong interaction (i.e., to gluons) must be very much suppressed. In the Standard Model of particle physics there then still remain the weak interactions, and in fact a weakly interacting massive particle (a "WIMP") seems to very well fit the bill. To find the feebly interacting WIMPs, various methods from astrophysics, nuclear and atomic physics, and particle physics such as at CERN are presently being combined for an exciting hunt. Astrophysical evidence for dark matter, e.g. in the form of “dark stars”, pioneered by Katie Freese in our group, belongs to the exciting hunt for possible effects of dark matter that we pursue.

Another interesting dark matter particle, the axion, was proposed by our present colleague here at Stockholm University, the Nobel Laureate in Physics 2004, Frank Wilczek. We recently (Dec. 2016) hosted a Nordita Workshop on this theme, and this is a topic that will certainly flourish at SU during the coming years, with Frank Wilczek a recipient of a prestigious ERC grant aimed at this topic.

Using the energetic cosmic rays that come to the Earth from outer space new information about particles and their interactions can be obtained. One recent example is the discovery of a non-zero mass of the neutrino by studying solar or cosmic ray induced muon and electron neutrinos (e.g., in the Super-Kamiokande experiment in Japan, or SNO in Canada; Nobel Prize to T. Kajita and A. MacDonald, 2015). Neutrino mixing is important to include in predictions of the dark matter induced neutrino flux from the center of the Sun or the Earth, something that Joakim Edsjö in our group has developed.

A large computer package, DarkSUSY, is currently maintained by Joakim Edsjö in our group and Torsten Bringmann (Oslo). We have also investigated so-called Kaluza-Klein models for dark matter. (By the way, did you know that Oskar Klein was a professor at Stockholm University? He has, of course, given the name to our Centre.)

We work in close contact with other theory groups in the world and with the experimental astroparticle physics groups at Fysikum (Fermi-LAT Gamma-ray Telescope, IceCUBE neutrino experiment at the South Pole) and the KTH (antimatter searches, PAMELA) which aim at detecting or putting limits on these dark matter candidates. We have performed theoretical calculations of the fluxes of neutrinos, gamma-rays, positrons and antiprotons which are the result of annihilation of supersymmetric particles or other WIMPS, if they make up the dark matter halo of the Milky Way. We also collaborate with Jan Conrad and his experimental group here at CoPS studying dark matter direct detection through scattering (XENON 1t is currently world leading in this field).

An international textbook, Cosmology and Particle Astrophysics, by Lars Bergström in our group and Ariel Goobar in the observational cosmology group, was published by Springer/Praxis (Germany) in 2003, with a student-priced paperback edition in 2006.

The astroparticle phenomenology part of the CoPS group consists presently of Lars Bergström (professor), Joakim Edsjö (professor), Katie Freese (professor), Frank Wilczek (professor – also in the condensed matter group) and Doug Spolyar (assistant professor, presently on sick leave). Thomas Schwetz-Mangold was with us for a couple of years, but left for KIT Karlsruhe in 2016. Present graduate students are Sebastian Baum, Carl Niblaeus, Sunny Vagnozzi, and Axel Widmar. Previously graduated with  a PhD include Michael Gustafsson (postdoc at University of Göttingen), Mia Schelke, Torsten Bringmann (associate professor at Oslo University), Anders Pinzke (postdoc in Copenhagen, now in industry), Pat Scott (now Ernest Rutherford Fellow at Imperial College, London), Yashar Akrami (postdoc in Leiden), Sara Rydbeck (Hamburg) and Natallia Karpenka (Southampton). Former graduate student Edvard Mörtsell is now lecturer in observational cosmology here in the CoPS group. Postdocs: Stefan Hofmann (now at LMU Munich), Anne Green (now at Nottingham University). Some other postdocs: Lidia Pieri (now at Udine/Trento/Padova/Paris), Malcolm Fairbairn (now at Kings College London) and Gabrijela Zaharijas (now at SISSA, Trieste). In the Oskar Klein Centre, we have had in our field as postdocs Rachel Rosen, Chris Savage, Fabio Iocco, Timur Delahaye, Miguel Pato, Abram Krislock and Florian Kühnel.

This text was updated in February 2018 – apologies if it is already outdated in this quickly moving field!