ProfessorArttuRajantie

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The overall theme of my research is the application of particle physics theories to cosmology. This is a field that is rapidly growing and gaining importance. Particle experiments such as the LHC at CERN and cosmological observations such as the Planck satellite are producing new data which can tell us a great deal about the very early Universe. However, making full use of them requires new, more sophisticated theoretical methods to carry out reliable calculations in the quantum field theories of particle physics. This direction of research will become even more important in the future because particle accelerator experiments will not be able to reach significantly higher energies that the 14 TeV limit of the LHC. Therefore cosmology is the only realistic way of probing physics at much higher energies.

The main focus of my research is on determining observable signatures, such as density perturbations or gravitational waves, produced by non-equilibrium field theory events in the early Universe, for example the end of the period of cosmological inflation or symmetry-breaking phase transitions predicted by the Standard Model of particle physics and grand unified theories. On one hand, these studies provide new ways to test fundamental theories about inflation and high energy physics, and on the other hand they can shed light on some of the deepest puzzles about our Universe such as the origin of matter.

Another central area of my research is the physics of topological solitons in quantum field theory, for example magnetic monopoles. These hypothetical particles with magnetic charge are predicted by string theory and grand unified theories. I am involved in the MoEDAL experiment, which is looking for magnetic monopoles and other exotic particles produced at the LHC.

Amazingly, there are also many similarities between the fundamental theories of particle physics and some condensed matter systems such as superconductors, superfluids and spin ices. I am exploring these connections, trying to find ways to to do "cosmology in the laboratory" - test cosmological theories with laboratory experiments. 

I enjoy doing outreach and telling school children and the general public about my research, and about cosmology and particle physics more generally. I have visited several schools both in the UK and in Finland. If you would like to arrange a visit, place let me know. Some talks I have given recently are:

• Primary School: The Universe
• Secondary School (GCSE and A-level): Big Bang and Expanding Universe; Creation of Matter, What does the Higgs Say?, Magnetic Monopoles

I have also given public talks, for example as part of Pint of Science, and Worldcon 75, and participated in popular science events such as Science Uncovered, I'm a Scientist and Royal Society Summer Science Exhibition, where I was the lead organiser of the Monopole Quest exhibit in 2015.

Talks

• Higgs instability during inflation and non-minimal coupling to gravity, CERN, 14 January 2015
• Anisotropic Gravitational Wave Background from Preheating
  Cambridge, UK, 4 February 2013 
• Perturbations from Preheating and Phase Transitions,
  Lorentz Center, Leiden, the Netherlands, 6 September 2011
• Perturbations from preheating,
  Out-of-Equilibrium Quantum Fields in the Early Universe, RWTH Aachen, 6-8 September 2010
• Non-Gaussianity from preheating,
  PASCOS-08, Perimeter Institute, 3 June 2008
• Non-Gaussianity from preheating,
  Cosmo-07, Brighton, 24 August 2007
• The end of locked inflation,
  DAMTP, University of Cambridge, 27 May 2005

Media Coverage

• Space.com: Did Gravity Save the Universe from 'God Particle' Higgs Boson?
• Astronomy magazine: Gravity may have saved the universe after the Big Bang
• Mail Online: Did gravity save the universe after the Big Bang?

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Introductory articles

• A. Rajantie, "The search for magnetic monopoles",  Physics Today 69, 10, 40 (2016) (free access)
• A. Rajantie, "Introduction to magnetic monopoles", Contemporary Physics 53 (2012) 195 (free access)

Talks

• Quantum Field Theory of Magnetic Monopoles?, TU Munich, 21 May 2015
• Magnetic Monopoles - Theory and Experiment,  University of Liverpool, 6 November 2013
• Magnetic Monopoles - an Overview, EPNT13, Marseille, France, 3 April 2013 
• Magnetic Monopoles in the Cosmos and at the LHC, MoEDAL Physics Workshop, CERN, 20 June 2012 
• Magnetic Monopoles in Field Theory and Cosmology (audio), Kavli Centre, 17 October 2011
• Soliton Form Factors from Lattice Simulations, Confining Flux Tubes and Strings, ECT*, 6 July 2010
• Quantum monopoles and critical kinks, TU Darmstadt, 13 November 2009
• ''t Hooft-Polyakov monopoles on the lattice, University of Wales Swansea, 19 May 2005
• ''t Hooft-Polyakov monopoles on the lattice, Kavli Institute for Theoretical Physics, University of California Santa Barbara, 23 March 2005
• Quantum solitons and dualities on a lattice, (Video), LMS Durham Symposium: Topological Solitons and their Applications, Durham, UK, 2-12 August 2004

Media Coverage

• Sunday Times: Hadron collider to hunt the 'yeti'
• Science News: Magnets with a single pole are still giving physicists the slip

Talks

• Defect Formation (video), Nordita, Stockholm, 1 July 2009
• Formation of Cosmic Strings in Gauge Field Theory, KITP, Santa Barbara, 25 February 2008
• Defects in 2PI, University of Manchester, 1 November 2006
• Formation of Local Cosmic Strings, Cosmo-06, Lake Tahoe, CA, 28 September 2006
• Gauged cosmic strings and superconductor vortices, Coslab 2005, Smolenice, Slovakia, 28 August - 4 September 2005 (videos 1 )
• Cosmic strings and high energy physics, Kavli Institute for Cosmological Physics, Chicago, IL, 4 March 2005
• Topological defects from gauge symmetry breaking, University of Illinois at Urbana-Champaign, 1 March 2005
• Vortex formation in a superconductor quench, Nanostructured Superconductors", Bad Munstereifel, Germany 15-19 May 2004

Heavy Cosmic Strings

Fast cooling (σ=0.00025)

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Slow cooling (σ=0.000025)

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These videos show the formation of the string network in two simulations with different cooling rates. The colours of the walls show the phase angle of the Higgs field in the Coulomb gauge. In the early parts of the videos, the white areas show the bubbles of the broken phase (high value of φ²) and in the later parts, they show the areas where the symmetry is unbroken (low φ²), i.e., the strings.

• Novel Astrophysical Probes of Dark Matter, Royal Astronomical Society, 12 March 2021
• Topological Avatars of New Physics, Royal Society, 4-5 March 2019
• Higgs Cosmology meeting, Chicheley Hall, 27-28 March 2017
• Kibble 80, Member of the Organising Committee
• Non-Equilibrium Field Theory in Cosmology, Chairman of the Organising Committee
• Numerical Cosmology 2012, Member of the Organising Committee
• COSMO-11, Convenor of the Inflation and Phase Transitions session
• PASCOS-08, Member of the International Advisory Committee
• Salam 50, Member of the Organising Committee
• PASCOS-07, Chairman of the Organising Committee
• COSLAB-04,  Member of the Scientific Committee
• COSMO-03, Parallel session convenor