Theoretical Particle Physics

Particle Cosmology

This area of research studies the interplay between Particle Physics and Cosmology during the early history of the Universe. It hence has close ties with the Astronomy centre.

Gravitational waves

Gravitational waves provide an exciting new window to the earliest stages of the universe. First order cosmic phase transitions may generate a gravitational wave signal strong enough to be probed by upcoming space based interferometers, such as LISA. Our group aims to determine the gravitational wave spectrum of phase transitions at the necessary precision. We also use gravitational waves to test modifications of general relativity.


Measurements of, in particular, the cosmic microwave background radiation seem to suggest that the universe went through a period of rapid expansion in the first 10-35second. Further still recent observations of supernovae suggest that the universe has re-entered a period of acclerated expansion of a very different scale of magnitude. Our group is involved in trying to construct realistic models in order to try and explain these two periods of inflation.

Cosmic Strings

Modern theories predict that after inflation ended the hot matter in the Universe may have gone through one or more phase transitions as it expanded and cooled. Phase transitions may have given rise to topological defects such as cosmic strings, and may provide an explanation for the baryon asymmetry of the Universe. A simulation of abelian Higgs strings can be downloaded from here.


The baryon asymmetry, a mysterious excess of matter over antimatter in the Universe, is one of the greatest puzzles in particle cosmology. We investigate if this asymmetry was created at the electroweak phase transition. This requires an extension of the standard model, such as supersymmetry or extra Higgs fields. We study properties of the phase transition in these models and investigate the related transport processes to determine the generated baryon asymmetry. Our aim is to derive reliable predictions which will allow to test this hypothesis in the near future at the LHC and electric dipole moment experiments.

Dark Matter

From many observations we know that most matter in the universe is not visible, i.e. it is dark. Several hypotesis on the nature of dark matter has been proposed, but the resulting dark-matter candidates have not been observed yet. Our group is involved in devising new models for dark matter, and explore the possibility that dark-matter candidates can actually be seen at colliders, especially at the LHC.

Related members:

Xavier Calmet, Mark Hindmarsh, Stephan Huber, Veronica Sanz