Study of the origin of supersymmetry breaking from phenomenology and cosmology point of vieu

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Broken supersymmetry has been a promising canditate for solving the naturalness problem of the standard model of particle physics. If this framework is real, it is crucially important to reveal the nature of the mechanism of supersymmetry breaking. The purpose of this research project is to obtain new insights on the search of the origin of the super-symmetry breaking by exploring various phenomenological and cosmological implications associated with the supersymmetry breaking.Among other things, the most notable results are 1. in the low-energy supersymemtry breaking scenario, there appears a very light gravitino (the superpartner of graviton) which may play a role of the dark matter of the universe. A detailed study of the comological structure formation in the gravitino dominated universe was done, and it shows that it does not reproduce the universe we observe now. This fact is a severe difficulty of the light gravitino dark matter scenario. 2. Recent developments of string theory have revealed the richenss of the vacuum structure of the string theory, which has stimulated to consider new frameworks of string phenomenology. For example the heterotic M-theory, a description of strongly interacting heterotic string theory, can explain the unification of gauge couplings in a natural way. Motivated by these developments, we investigated details of the supersymmetry breaking via the gaugino condensation scenario and clarified similarities and differences on the nature of the supersymmetry breaking as well as the superparticl mass spectra, in comarison with the conventional weak coupling regime. In addition to the results above, we obtained, for example, interesting results on axion physics when combined with various mechanisms of the sup ersymmetry breaking.