Detecting Extra-dimensions through Cosmic Background Radiation

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Recent observation on cosmic background radiation by WMAP strongly supports the validity of the inflationary scenario. Nowadays, the most important issue in theoretical cosmology is to unveil the inflaton. On the other hand, it is widely believed that the superstring theory is the most promising candidate of the ultimate unified theory of everything. The most precise prediction of superstring theory is that our world is 10-dimensions. That means the extra 6-dimensions must be compactified to the small size to reconcile with our real world. Recent developments of superstring theory suggest the braneworld picture as a mechanism of compactification. We have unveiled the inflaton based on this new picture of the world, namely braneworld. Firstly, we have constructed the 4-dimensional effective theory describing the low energy dynamics of the braneworld by using the gradient expansion method invented by us. Then, using this effective theory, we have analyzed the collision process of two braneworlds. At the collision point, we have utilized the purely 5-dimensional analysis. The point is that we have constructed the geometrical inflation model. In our inflationary model, Inflation is caused by the flux in the bulk and terminated by the collision of braneworlds. The heat produced by the collision ignites the big-bang of our universe. We have also calculated the cosmological perturbations produced by the quantum process during rapid expansion and shown that the predictions are consistent with the present observations.