Lattice Investigations of Physics Beyond the Standard Model

Who: Martin Hansen (CP3-Origins)
When: Monday, February 22, 2016

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The discovery of a new scalar state, in agreement with the theoretical predictions for the Higgs boson, was a tremendous success for the Large Hadron Collider and for the Standard Model of particle physics. Nevertheless, from a theoretical standpoint the Higgs sector is quite unappealing. Partly because it only models spontaneous symmetry breaking, rather than offering a dynamical explanation, but mostly because it does not protect the electroweak scale against large quantum corrections.

In this thesis we consider an alternative realisation of the Higgs sector in which some of these problems are solved by introducing a new strongly interacting sector. In this class of models, termed Technicolor models, the electroweak symmetry is broken by the formation of a chiral condensate and the Higgs boson is identified with the lightest scalar excitation.

Lattice field theory is currently the only known method for studying the dynamics of strongly interacting models, because conventional perturbation theory breaks down at strong coupling. We will use these methods to study one of the most promising Technicolor candi- dates, commonly known as the sextet model. The main objective of the study is to determine whether the model is conformal or chirally broken, because the dynamics is quite different in the two scenarios.

Lattice simulations must be extrapolated to the chiral limit and to this end we need predictions for the model’s behaviour in this regime. Assuming the model is chirally broken, the behaviour of the pseudoscalar mass and its decay constant can be calculated by writing down an effective Lagrangian for the model. This approach is known as chiral perturbation theory and it has proven to be one of the most powerful tools for studying the low-energy spectrum of strongly interacting models. We will introduce this method and show explicitly how to calculate the low energy behaviour of the pion mass and its decay constant.

The master thesis is available as a PDF file.