Curvaton mechanism and its implications to sneutrino cosmology

In the study of the evolution of the universe, it is important to understand the origin of the cosmic density fluctuations. The most conventional scenario is inflation [1] where quantum fluctuation of the inflaton field during the inflation becomes the origin of the cosmic density fluctuations. From the particle-physics point of view, it is desirable to construct a model of inflation which is testable by collider (or other laboratory) experiments; if it is possible, we can study the mechanism of the cosmological density fluctuations with collider experiments. It is, however, difficult to construct such a testable model of inflation since the requirements on the inflaton potential is very stringent. Recently, a new mechanism of generating the cosmic density fluctuations has been attracting many attentions, where a late-decaying scalar condensation provides the dominant source of the cosmic density fluctuations. In this scenario, dominant part of the cosmic density fluctuations originate from the primordial fluctuation of a new scalar field, called “curvaton,” which is different from the inflaton field [3,4,5]. Even though, in a large class of the curvaton scenario, inflation is assumed as a solution to the horizon and flatness problems as well as to generate the primor-