Supersymmetry breaking and its implication to cosmology

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In this work, I have studied cosmology in the framework of particle-physics models with low-energy supersymmetry. In particular, I have paid particular attention to 1) origin of the density fluctuation of the universe, and 2) big-bang nuclesynthesis.On the first topics, I have considered the case where there exists some scalar field (other than the inflaton) which once dominates the universe in the early epoch. If such a scalar field acquires primordial amplitude fluctuation, it may become the origin of the present density fluctuation of the universe. (Such a scalar field is called the "curvaton" field.) There are various candidates of the curvaton field in supersymmetric models. I have considered the case where the right-handed scalar neutrino plays the role of the curvaton field, and possible signals in such a case. I also discussed the implication of the curvaton scenario for the so-called D-term inflation model in supersymmetric model.On the second subject, I considered the effects of the decay of the gravitino, which is the superpartner of the graviton, on the big-bang nucleosynthesis. I have performed a detailed calculation of the decay rate of the gravitino and obtained a precise information about the decay products of the gravitino. Then, I have studied the effects of those decay products on the light-element abundances. I have obtained a very reliable upper bound on the reheating temperature after the inflation using this calculation.