Proton Decay and Sub-Structure

The problem of elementarity of electric charge is investigated. It is known that possible proton decay is caused by $X$ and $Y$ bosons which are characteristic in GUTs. The charge structure of GUTs is, however, not simple, and the five types of charge units appear. We investigate the problem of elementarity in taking into account of the simplest model of the charge structure known as the rishon model, where the charge units are known as 1/3 ($T$) and 0 ($V$). In order to approach to sub-structure together with the problem of simplicity of charge structure, possible rearrangements of rishons are investigated on the basis of color and hypercolor confinement condition. Further, possible existence of the simplest electroweak sub-structure is discussed. Our model predicts possible proton decay mode, in which $X$ and $Y$ bosons are not concerned.