Cosmological physics

Extensions of the standard model of elementary particles based on Kaluza-Klein theory, string theory and other theories with extra dimensions, involve typically many new fields when observed from our four-dimensional spacetime. In particular, there is alw ays one or more scalar fields which appear with gravitational interactions and can have important consequences both in cosmology and in elementary particle physics. The main objective of this project is to investigate the cosmological implications of the scalar radion field in a special theory with two extra dimension. First of all one must make sure that the generic variation with time of the gravitational constant is conssistent with observations and nucleosynthesis. This scalar field can also provide a natural mechanism for the rapid expansion of the Universe during the inflationary phase just after Bing Bang. Similarly, it can also be responsible for the dark energy or quintessence which is seen in the form of the present-day acceleration of the Universe. In a more complete treatment of the extra dimensions, the other scalar fields which appear with similar pr operties, should eventually also be included in the investigation.