O potencial efetivo a temperatura finita no modelo padrão

Abstract

The theory of elementary particles has symmetries, spontaneously broken by scalar fields when they develop a vacuum expectation value different from zero at the minimum of the effective potential. So, as the universe cools, it goes through a series of first- and secondorder phase transitions between potential minima. The strong first order electroweak phase transition will be the focus of this dissertation, in order to try to understand the criteria for having baryogenesis. To understand the history of the universe, we need to analyze the density of the particles that compose it and how these particles behave over time. In the early days of the universe, it was so compact and hot that the formation of light elements was impossible, as the annihilation of particles-antiparticles and the energy of the remaining particles was greater than necessary for the combination of constituents of an atom. This universe, due to these high energies, was in equilibrium, we see that phenomena that disturb this balance play a role in the formation of these elements. When the universe expands, temperatures decrease and also the energies of the particles that compose it, therefore, it is necessary to evaluate the thermodynamics of the primordial universe and what its role in the formation of elements. For the universe to have a baryonic number other than zero, some symmetries need to be broken. As previously stated, the spontaneous symmetry breaking at the beginning of our description needs to be evaluated, we then need to describe the expectation value of the vacuum with the potential at the tree level, after which we will find the 1-loop correction at zero and finite temperature. The ratio between the minimum value of the potential and the temperature is a way to measure the strength of the phase transition. If we impose that this ratio must be greater or equal to one, we find a limit for the Higgs mass of 45 GeV that differs from the current values found at the LHC, which is 125.25 GeV.