Desert (particle physics)

In the Grand Unified Theory of particle physics (GUT), the desert refers to a theorized gap in energy scales, between approximately the electroweak energy scale–conventionally defined as roughly the vacuum expectation value or VeV of the Higgs field (about 246 GeV)–and the GUT scale, in which no unknown interactions appear. It can also be described as a gap in the lengths involved, with no new physics below 10−18 m (the currently probed length scale) and above 10−31 m (the GUT length scale). The idea of the desert was motivated by the observation of approximate, order of magnitude, gauge coupling unification at the GUT scale. When the values of the gauge coupling constants of the weak nuclear, strong nuclear, and electromagnetic forces are plotted as a function of energy, the 3 values appear to nearly converge to a common single value at very high energies. This was one theoretical motivation for Grand Unified Theories themselves, and adding new interactions at any intermediate energy scale generally disrupts this gauge coupling unification. The disruption arises from the new quantum fields- the new forces and particles- which introduce new coupling constants and new interactions that modify the existing Standard Model coupling constants at higher energies. The fact that the convergence in the Standard Model is actually inexact, however, is one of the key theoretical arguments against the Desert, since making the unification exact requires new physics below the GUT scale. All the Standard Model particles were discovered well below the energy scale of approximately 1012 eV or 1 TeV. The heaviest Standard Model particle is the top quark, with a mass of approximately 173 GeV. Above these energies, desert theory predicts no particles will be discovered until reaching the scale of approximately 1025 eV. According to the theory, measurements of TeV-scale physics at the Large Hadron Collider (LHC) and the near-future International Linear Collider (ILC) will allow extrapolation all the way up to the GUT scale.