O momento magnético anômalo do múon e os modelos de dois dubletos de Higgs

Abstract

In this work, we overview the evolution in the understanding of the magnetic dipole moment for leptons. We begin by showing that the classical analysis of the ratio between this quantity and the particle’s spin is mistaken and must be corrected by a dimensionless g factor. We then comment on how experiments in Schrödinger’s quantum mechanics impose g = 2, while Dirac’s later theory for the relativistic electron predicts this result from first principles. Subsequently, we elaborate on how Quantum Field Theory introduces vacuum fluctuations that were first necessary to explain the Lamb shift in the hydrogen atom. These same effects correct the g factor, motivating us to talk about the (g − 2)/2 anomaly. This quantity depends not only on Quantum Electrodynamics (QED), but also on the electroweak and strong interactions that define the Standard Model (SM) and are explored in sequence. However, this theory presents several problems, one of which is the disagreement between the prediction for the value of the muonic anomaly and its experimental observation. So we explore a simple extension of the electroweak sector called the two Higgs doublet model (2HDM) to resolve the anomaly. It is shown at the end for the lepton-specific version (type X) that there is a region of the parameter space capable of eliminating the discrepancy.