Professor Lars Bergström
Department of Physics
Stockholm University, AlbaNova University Centre
S-106 91 Stockholm, Sweden
tel: (+46)(0)8-5537 8725
fax:                            8601

e-mail: lbe@physto.se

Basåret, Fysik A, 2012-13

Cosmology, Particle Astrophysics and String Theory (CoPS) Group

Part of the HEAC excellence center—read more on the HEAC homepage

NEW! Major grant from the Swedish Science Research Council (VR): The Oskar Klein Centre for Cosmo Particle Physics

In recent years, the connections between the science of the smallest constituents of the Universe (particles or perhaps strings) and the science of the largest structures in the Universe - including the Universe itself and its evolution, cosmology - have become ever stronger. There are many reasons for this. One is the fact that the current cosmological ``standard model'' - the Big Bang model - implies that the earliest stages of the Universe (the first fractions of a second) were dominated by the particles (quarks, leptons and force carriers) whose properties can only be intensively studied at accelerators.

Another reason is that with the help of particles such as gamma rays, neutrinos, protons and antiprotons, there is a possibility to learn more about many astrophysical processes which have traditionally only been studied by low-energy electromagnetic radiation (light and radiowaves).

Using the energetic cosmic rays that come to the Earth from outer space new information about particles and their interactions can also be obtained. One recent example is the discovery of a non-zero mass of the neutrino by studying cosmic ray induced muon and electron neutrinos (in the Super-Kamiokande experiment in Japan).

The astroparticle theory part of the CoPS group consists presently of Lars Bergström (professor), Joakim Edsjö (assistant professor), Michael Gustafsson (now Postdoc at University of Padova, Italy), Torsten Bringmann (PhD 2005 – now at Hamburg University), Anders Pinzke (on his way to a postdoc at UC Santa Barbara), Yashar Akrami, Sara Rydbeck and Natallia Karpenka (graduate students) . During 2003 and 2004, Stefan Hofmann was a postdoc in our group (then at the Perimeter Institute and NORDITA Stockholm October 2007 – December 2008, now at LMU Munich). Anne Green  was a postdoc in the group (now permanent position at Nottingham University). Former graduate student Edvard Mörtsell had a research assistantship at the Astronomy Department in the same house (AlbaNova), and has just started a on a lectureship of observational cosmology here in the CoPS group. Postdocs from Autumn 2004 were Lidia Pieri (now at Udine/Trento/Padova/Paris) and Malcolm Fairbairn (now at CERN and permanently at King’s College London). November, 2008 to November 2009, Gabrijela Zaharijas was a postdoc here. Now, with the Oskar Klein Centre, we have Rachel Rosen, Chris Savage, Antje Putze and Alessandro Cuoco as postdocs.

The group is involved in several activities. One of the main lines of research is to investigate the nature of dark matter which seems to dominate the mass density of the Universe. In particular, we focus on a class of candidates called supersymmetric particles, which are predicted to exist in superstring models, but also extended Higgs models, for example.
A large computer package, DarkSUSY, has been developed with our participation and is currently maintained by Joakim Edsjö. 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 new 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: see below, IceCUBE neutrino experiment at the South Pole: Klas Hultqvist and others) and the KTH (antimatter searches, PAMELA: M. Pearce) 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 antiprotons which are the result of annihilations of supersymmetric particles, if they make up the dark matter halo of the Milky Way.

Other projects that we currently work on include Big Bang nucleosynthesis, the Cosmic Microwave Background, transplanckian physics, physics of branes in extra dimensions and gravitational lensing of quasars and supernovas.

We are especially involved in theoretical analyses in connection with the Fermi-LAT Gamma-ray satellite (launched in June, 2008), which has a substantial Swedish participation. The present experimental leader of the dark matter detection effort is Jan Conrad here in CoPS, with whom we collaborate a lot (see, e.g. this paper). With a graduate student, Anders Pinzke, (now postdoc at UC Santa Barbara, USA) we have used a large N-body simulation of gamma-rays formed in formation of structures like galaxy clusters, to get an idea of realistic backgrounds for the dark matter search. There are also plans for a new satellite, JDEM/SNAP/Euclid for which we are making pre-studies in collaboration with Ariel Goobar.

A text-book on astroparticle physics, Cosmology and Particle Astrophysics, by Lars Bergström and Ariel Goobar was published in 1999 by Wiley/Praxis (England). It has been rewritten as an enlarged second edition, published by Springer/Praxis (Germany) in December 2003. A student-priced (paperback) edition appeared in 2006.

This text was updated February24, 2011— I apologize if it is incomplete and already obsolete!