Academic Interests

I am a theoretical physicist with a strong interest in computational physics and many-body theory in general, and the nuclear many-body problem and nuclear structure problems in particular. This means that I study various methods for solving either Schrödinger’s equation or Dirac’s equation for many interacting particles, spanning from algorithmic aspects to the mathematical properties of such methods. The latter also leads to a strong interest in computational physics as well as computational aspects of quantum mechanical methods. A large fraction of my work, in close collaboration with colleagues at Michigan State University, the University of Oslo, Oak Ridge National Laboratory as well as many other institutions worldwide, is devoted to a better understanding of various quantum mechanical algorithms. This activity leads to strong overlaps with other scientific fields. Although the main focus has been and is on many-body methods for nuclear structure problems, I have also done, and continue to do, research on solid state physics systems in addition to studies of the mathematical properties of various many-body methods.

The applications to many-body problems in nuclear physics lead also to many interactions with experimentalists and various experimental programs. The theories I participate in developing, have as final aims to be able to explain correlations in complicated many-body systems like nuclei and dense nuclear matter.

Why the nuclear many-body problem, you may ask. Well, for me, to understand why matter is stable, and thereby shed light on the limits of nuclear stability, is one of the overarching aims and intellectual challenges of basic research in nuclear physics and science. To relate the stability of matter to the underlying fundamental forces and particles of nature as manifested in nuclear matter is central to present and planned rare isotope facilities.

Examples of important properties of nuclear systems that can reveal information about these topics are masses (and thereby binding energies), and density distributions of nuclei. These are quantities that convey important information on the shell structure of nuclei with their pertinent magic numbers and shell closures, or the eventual disappearance of the latter away from the valley of stability.

Neutron-rich nuclei are particularly interesting. As a particular chain of isotopes becomes more and more neutron rich, one reaches finally the limit of stability, the so-called dripline, where one additional neutron makes the next isotopes unstable with respect to the previous ones. In a recent article published in Phys. Rev. Lett. 109, 032502 (2012) we computed several properties of calcium isotopes, including three-body forces, a much debated and studied issue in nuclear many-body theory. Our calculations predict the dripline of the calcium isotopes at mass 60, partly in conflict with present results from mean-field and mass models used in astrophysical calculations. To understand the limits of stability of the calcium isotopes is one of the benchmarks experiments of the coming Facility for Rare Isotope Beams at Michigan State University. The computed first excited 2+ state for calcium-54 was later observed in an experiment published in Nature in 2013, confirming our theoretical predictions.

A promising recent development involves a proper parametrization of the strong force, resulting in better Hamiltonian for nuclear physics studies. Combining very powerful effective field theory derivations of the nuclear interaction and multidimensional optimization techniques, we were able to generate a very precise two-body interaction that reproduces experimental data in neutron rich oxygen and calcium isotopes.

My activity is described in more detail under the webpages of the Computational Physics group. The research group on Computational Physics at the Department of Physics of the University of Oslo, has its main focus on the development of theoretical and computational methods for quantum mechanical and statistical mechanics systems. Our research spans from dense matter such as neutron stars to the flow of liquids in porous media.

Our core research is structured into three main areas, offering thereby a wide perspective on thesis projects: theoretical physics with an emphasis on quantum mechanics and statistical mechanics, computational physics/numerical mathematics and high-performance computing. Read more about our activities on Computational Quantum Mechanics and Computational Statistical Mechanics.

Here are some recent articles which reflect my research interests.

Hagen et al, Rep. Prog. Phys. 79, 096302 (2014), ´Coupled-cluster computations of atomic nuclei´ Hagen et al, Phys. Rev. C 89, 014319 (2014), ´ Coupled-cluster calculations of nucleonic matter´ Ekström et al, Phys. Rev. Lett. 110, 192502 (2013) ´Optimized Chiral Nucleon-Nucleon Interaction at Next-to-Next-to-Leading Order´ Baardsen et al, Phys. Rev. C 88, 054312 (2013) ´ Coupled-cluster studies of infinite nuclear matter´ Ø. Jensen et al, Phys. Rev. Lett. 107, 032501 (2011) ‘Quenching of Spectroscopic Factors for Proton Removal in Oxygen Isotopes’ G. Hagen et al, Phys. Rev. Lett. 109, 032502 (2012) ‘Evolution of Shell Structure in Neutron-Rich Calcium Isotopes’’ M. Pedersen Lohne et al, Phys. Rev. B 84, 115302 (2011), ‘Ab initio computation of the energies of circular quantum dots M. Hjorth-Jensen, Physics 4, 38 (2011), ‘The carbon challenge’ D. J. Dean and M. Hjorth-Jensen, Rev. Mod. Phys. 75, 607 (2003), ‘Pairing in nuclear systems: from neutron stars to finite nuclei’ Teaching In addition, I’m strongly involved in teaching at all levels. I have been heading the bachelor program Physics, Astronomy and Meteorology ( FAM ) in the period 2002-2011. I am also strongly involved in the project Computing in Science Education. Furthermore, with European and American colleagues, we have established the recent successful Nuclear Talent initiative.

Please feel free to come by and discuss. I teach now the following courses at the University of Oslo and Michigan State University:

FYS3150 Computational Physics I, Fall semester, senior undergraduate level (Oslo) FYS4411 Computational Physics II: Quantum mechanical systems, M.S and PhD level, Spring semester (Oslo) FYS-KJM4480 Quantum mechanics for many-particle systems, M.S. and PhD level, Fall semester (Oslo) PHYS-981 Nuclear Structure, M.S. and PhD level, Spring semester 2013-2015 (MSU) Advanced courses In 2015 the Nuclear Talent initiative organizes three new courses for graduate students in nuclear physics. I will, together with several colleagues teach the course on nuclear many-body theory. I will also lecture at the doctoral training program of the ECT* in Trento in Italy, as well as at the National Nuclear Physics summer school organized by the Institute of Nuclear Theory in Seattle. During the last ten years I have taught advanced nuclear physics topics at several schools, totaling more than 200 one hour lectures. In 2015 I will teach at

The nuclear Talent Course on many-body methods for nuclear physics , GANIL, Caen, France, July 5-25 The ECT* Doctoral training program, ECT*, Trento, Italy, April 13-May 22 National Nuclear Physics summer school, Lake Tahoe, California, June 15-25 Background and education I have been a Professor in theoretical nuclear physics at the University of Oslo since May 1 2001 and since January 2012 I am also a Professor in theoretical nuclear physics at Michigan State University. I was an associate professor at the same university in the period January 1 1999 to April 30 2001.

I got my PhD in theoretical nuclear physics in December 1993 at the University of Oslo. I received my Siv. Ing. (Master of Science equivalent) degree in March 1988 at the Technical University of Norway (NTH) in Trondheim. In the period August 1989 till December 1993 I was a research assistant (PhD studies) at the University of Oslo and a research associate in the period January 1 till September 30 1994 at the same place. In the period October 1 1994- December 1998 I was a post-doctoral fellow at the European Center for theoretical studies in nuclear physics, ECT* , in Trento, Italy and at the Nordita in Copenhagen, Denmark. I was an adjunct Professor in theoretical Nuclear Physics at Michigan State University from 2003 till 2011. I was a visiting professor at CERN from September 2004 till June 2005.

Service to the community (editorial boards etc) Editorial board member of the European Journal of Physics A (2010-2016) Editorial board member of Physical Review C (2014-2016) Editorial board member of Lecture Notes in Physics (2010-2016) Editorial board member of the Special Topics issue of the European Journal of Physics Member of the NSCL PAC (2003-2008) Panel member for the Canadian Research council (2013-2015) Chair of the Nuclear Talent steering committee Awards and recognitions In December 2000 I shared the University of Oslo Excellence in Teaching Award with Arnt Inge Vistnes. In 2007 I became a fellow of the American Physical Society. In 2008, our team, David Dean, Gaute Hagen, Thomas Papenbrock and myself received the Oak Ridge National Laboratory award in the category for “Scientific Research” for our development and implementation of coupled-cluster theory for medium mass and neutron-rich nuclei. In 2008 I was recognized as an Oustanding Referee by the American Physical Society. In June 2011, the Computers in Science Education project was awarded with the Excellence in Teaching award at the University of Oslo, see the above link about the CSE project. The same project was awarded in 2012 the annual prize from ‘The Norwegian Agency for Quality Assurance in Education (NOKUT)’. Elected member of the Norwegian Academy of Science and Letters Elected member of The Royal Norwegian Society of Sciences and Letters You can find more about me and my research interests on Google Scholar, see http://scholar.google.com./citations?user=nuiyEmwAAAAJ