New Solutions to the Hierarchy Problem

The Standard Model (SM) is a very successful description of particle physics up to the weak scale. It agrees with all the experimental data we have our disposal today. However, it has several shortcomings. We do not know the origin of the fermion masses, which in the SM arise from the Yukawa interactions with the Higgs doublet. These are extremely varied, with a Yukawa coupling for the top of order one, and for the electron about 106 times smaller. This constitutes the fermion mass hierarchy problem. Its solution might lie at high energy scales so that experiments at the TeV scale might not necessarily explore it. Another question unanswered by the SM, refers to the so called gauge hierarchy problem: why is the weak scale so much smaller than the Planck scale. We believe that the answer to this problem is at the TeV scale and therefore accessible to the Large Hadron Collider (LHC). We will first briefly summarize the status of the SM in Section II. In Section III we will expose the gauge hierarchy problem in more detail. In Section IV we will presents a review of solutions to the gauge hierarchy problem involving compact extra spatial dimensions.