High Energy and Astroparticle Physics

High Energy and Astroparticle Physics

The energy scale at which Quantum Gravity becomes non negligible is the Planck scale of 1019~ \mathrm{GeV}. This is the energy at which the Compton wavelength of a lump of energy such as an elementary particle equals its Schwarzschild radius which then would force the particle to become a black hole. This is 16 orders of magnitude away from the best man made microscope to date which is the Large Hadron Collider (LHC) at the CERN with an energy resolution of a few \mathrm{TeV}. As such one would expect that one could safely ignore QG effects in all experiments in the forseeable future. While that is true for man made experiments it is wrong for processes that are relevant for astrophysics. Apart from the unknown physics that is going on close to the GR singularities as described above, ultra high energetic (UHE) cosmic rays are known to reach energies of the order of 1016~\mathrm{eV} which is only nine orders of magnitude away from the Planck scale. As we can probe the structure of space and time only with elementary particles, the above line of thought suggests that in fact it is meaningless to try to resolve energies beyond the Planck energy or distances beyond the Planck length of 10{-33}~\mathrm{cm} or times beyond the Planck time of 10{-43}~\mathrm{s}. This of course would have a tremendous conceptual impact on the foundations of QFT since then quantum space-time would resemble a discrete lattice rather than a continuum. Accordingly, research in Quantum Gravity is not at all of academic interest only and one can hope to find signatures in astroparticle physics. High energy physics, which uses the mathematical framework of QFT, most importantly scattering matrix theory and Feynman graphs, is of course also interesting in its own right for Quantum Gravity because every matter species couples gravitationally. Thus it makes a big difference whether or not the LHC discovers evidence for the Higgs particle and/or supersymmetry.