Περίληψη: | The Standard Model of Particle Physics is rightfully considered one of the most precise theories in physics, since it has given us a very good and accurate understanding of the Universe. Nevertheless, there are still open problems that this theory is unable to address. That is the topic of current theoretical research, in which scientists are trying to extent the physical and mathematical content of the Standard Model so as to provide plausible answers to these open problems. In this thesis we are particularly interested in the discrete symmetries of the elementary particles because we believe that they give rise to fundamental questions about the very nature of the particles and the cosmos. We first try to understand the symmetries of Parity, Charge Conjugation and Time Reversal along with their combinations and then we address their violation. These violations show us the reasons why we need to go beyond the Standard Model. After choosing a particular extension of it, namely the Grand Unified SU(5) model, we use it to give a plausible answer to the problem of Baryonic Asymmetry in the Universe which is directly connected to those discrete symmetries.
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