Probing beyond the standard model physics using effective field theory

Resumen

Now the LHC has provided 120 fb^{−1} of data, the evidence for an energy gap between the Standard Model (SM) and new physics has grown strong. This makes effective field theory (EFT) a versatile method to constrain new physics with minimal model dependence. In this thesis, based on work done during my PhD candidature [1–4], we make use of EFT techniques in a variety of studies. We start by exploring the prospect of extracting the Higgs trilinear self-coupling at current hadron and future lepton colliders, using both higher order corrections to the single-Higgs process and di-Higgs production. Our analysis minimizes model dependence thanks to the use of EFT. We argue that in order to constrain the different possible deviations to the Standard Model, a global fit with the inclusion of as many observables as possible is needed. We found that the inclusion of the trilinear correction in single-Higgs processes has a marginal effect at the LHC and will give a bound on the trilinear of order one. The situation is different at lepton colliders, where the high precision and different running energies can give bound of order 50%. We then extend our EFT by adding a scalar singlet to study the CP properties of the particle which could have been behind the infamous 750 GeV di-photon excess. We define the CP sensitive asymmetries, in both the vector and gluon fusion channels, and study their power to differentiate between the CP odd or even hypotheses. Finally, we move somewhat away from EFT, and use a simplified model to compare the constraints on composite Higgs models coming from low energy neutron and electron electric dipole moment (EDM) measurements and LHC searches. Effective field theory is not completely absent, since we compute the two loop corrections of the light quarks and leptons EDM to match our simplified model to the higher dimensional operators of a low energy effective Lagrangian, and obtain bounds for our model. We then recast LHC searches and compare the present and future bounds. We found that the current bounds are competitive with the one coming from the LHC direct search and are of order a few TeV. The future upgrade of the experiment measuring the electron dipole moment should bring the bounds to the 5-10 TeV range.