Brane-Antibrane Inflation in Orbifold and Orientifold Models
Abstract
We analyse the cosmological implications of brane-antibrane systems in string-theoretic orbifold and orientifold models. In a class of realistic string models, consistency conditions require branes and antibranes to be stuck at different fixed points, and so their mutual attraction generates a potential for the radius of the underlying torus. We find that this potential leads naturally to a period of cosmic inflation with the radion field as the inflaton. The slow-roll conditions are satisfied much more generically than the previously studied case with the branes free to move within the space. The appearance of tachyon fields at certain points in moduli space indicates the onset of phase transitions to different non-BPS brane systems, providing ways of ending inflation and reheating the corresponding observable brane universe. Besides the fact of being phenomenologically realistic and getting inflation more generically, this new scenario has several advantages over the case of toroidal compactifications, in relation to the `branegenesis' problem and the cosmological moduli problem. It also relaxes the assumption of frozen radius by promoting it into the inflaton field. As a successful inflation model it predicts an almost scale invariant spectrum of density perturbations.Keywords
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