Early Universe theories

Wednesday, April 28, 2010

What are the initial conditions to the Big Bang model? When analyzing the current data, most cosmologists (including myself) typically assume an almost scale invariant primordial spectrum of perturbations and Gaussian initial conditions. This is what one expects from Inflation and it elects the Lambda Cold Dark Matter model as the best fit to the data. In fact, there is no strong argument for just considering the simpler models and different assumptions (e.g. non-Gaussianity as discussed elsewhere) can greatly affect the extraction of cosmological parameters. For instance, phase transitions associated with spontaneous symmetry breaking during the inflationary era might have created features in the primordial spectrum of fluctuations. Such features are still compatible with current CMB and LSS data and may change the value of parameters such as the dark energy.

Another more speculative subject which I’ve explored is the so called braneworld scenarios, where it is proposed that we may live confined to a four dimensional brane in a higher dimensional spacetime. One interesting thing I did with others was to reexamine Wald’s no hair theorem for the global anisotropy in these type of universes. We showed that to have isotropization of the brane, the type of matter on it cannot be as general as in the four dimensional case. For example, the presence of a strong magnetic field, can lead the brane to collapse. The braneworld scenarios could provide new ways to approach old cosmological questions, such as the nature of dark matter or the cosmological constant problem.