I am a theoretical cosmologist. My research lies at interface between cosmology and particle physics. Specifically, I am interested how the accelerated expansion in the very early universe (inflation) and late universe (dark energy) can be explained within theories beyond the standard model. I also work on some aspects of cosmological perturbation theory and structure formation in diverse theories.


Dark Energy:

I am fascinated by dark energy, an energy form which is responsible for the current accelerated expansion of the Universe. It contributes about 70% of the total energy budget in the Universe and yet, we do not know much about it. There are good theoretical ideas for the other dark component we know of: dark matter. These are very likely new particles which we haven’t yet discovered directly on earth but extensions of the standard model of particle physics usually come with good theoretical candidates for dark matter. Dark energy, on the other hand, is of a different calibre. It is not that we don’t have a good working model in cosmology: it is called the cold dark matter model with the cosmological constant (ΛCDM). It explains the current data very well. The problem is that the cosmological constant (essentially an energy density constant in time pervading space) is very hard to explain in particle physics because the theoretical value is much bigger than what we observe. Therefore I study dynamical models of dark energy and their cosmological consequences. I want to learn in how far such models agree with observations.

On the other hand, the ultimate reason that the expansion of the Universe is accelerating may be a sign that Einstein’s theory of gravity (General Relativity, GR) is not the full answer. Therefore I study modifications of GR (under the name Modified Gravity). My research led me to study the cosmological consequences as well as to suggest local experiments. The exiting news is that laboratory experiments, such as ALPS or GammeV, can test these and put strong constraints on the parameter of these theories. By pursuing this avenue, we will learn a lot about how the phenomenon of dark energy could be embedded in particle physics theories.

In the next few years, cosmological experimental probes (e.g. the PLANCK satellite and the EUCLID mission) will provide very strong constraints on the properties of dark energy. Very important will also be the study of how dark energy affects non-linear structure formation. Therefore, I plan to develop analytical methods to study cosmological perturbations in the non-linear regime in the presence of dark energy.

Some of my publications in this area are:

Inflationary Cosmology:

The majority of cosmologist believe that there was another area of accelerated expansion, namely in the very early Universe. This period is called “Inflation”. There are good reasons to believe that inflation is part of the full story. In particular, the perturbations produced during an inflationary epoch agree with cosmological observations. But like dark energy, inflation has to be embedded in the context of particle physics. It is usually believed that one or several scalar fields have driven an inflationary period and my goal is study phenomenological models and their observational consequences. I have worked on a wide range of theories, such as those motivated from brane worlds, supergravity or scalar tensor theories in general.

Some of my publications in this area are:

Feel free to check out my full list of publications at Inspire or at Google Scholar.