The Axion Theory The Strong CP Problem One

The Axion Theory The Strong CP Problem One of the most important achievements in physics The standard model of particle physics Theory QCD predicts that CP (and T) symmetry is broken in strong interactions. Neutron Electric Dipole Moment – EDM Violation of CP symmetry ⇒ EDM of the neutron QCD energy scale ≈ 1 Ge. V Symmetry Conservation (Exp. ) C P CP Electromagn. Yes Yes Strong Yes Yes Weak No No No reduced mass of up and down quark Prediction by Theory Experimental limit M. Pospelow and A. Ritz Phys. 318 119 (2005) CP-Violating Parameter Effective QCD Lagrangian So far, CP violation has not been yet observed in QCD! C. A. Baker et al. 2006 (hex-exp/060220) Difference of a factor of =10 -10 between theory and experiment! The Way Out: the Axion The Peccei & Quinn Solution (1977) Introduce a massless pseudoscalar field a(x) interacting with the gluon field ⇒ field a has to be CP odd by construction The Axion A New Light Boson Particle interpretation by 1978: Steven Weinberg – “The Higglet”S. Weinberg Phys. Rev. Lett 40, 223 (1978) 1978: Frank Wilczek – “The Axion” F. Wilczek Phy. Rev. Lett. 40, 279 (1978) “I named them after a laundry detergent, since they clean up a long standing problem in theoretical physics. ” Some Basic Properties ⇒ Additional global symmetry (Peccei-Quinn symmetry) o Pseudoscalar particle similar to 0 o Light neutral Goldstone boson that couples to two photons o Very weak interaction probability with matter Alternative o Viable dark matter candidate for o New and unconventional physics Nuclear Interaction Nucleon Bremsstrahlung The Axion Emission Processes in Stars Electron Interactions Pair Annihilation EM Bremstrahlung Photon Coupling Pion Coupling Nucleon Coupling Primakoff Effect Compton Scattering Primakoff Effect Axion couplings Electron Coupling Photon Interaction Axion-photon coupling gives rise to the Primakoff effect: axion-photon conversion (and vice versa) in the presence of electromagnetic fields. This is the only axion phenomenology on which CAST relies… CAST is also sensitive to other axion-like particles [Any (pseudo)scalar coupled to the photon] Axion Searches One candidate for Dark Matter: Axion 1. Axions produced in the Sun: The history of the Universe – Axion Helioscopes CAST@CERN; Tokyo@Tokyo – Crystal detectors SOLAX; COSME@Canfranc; DAMA@Gran. Sasso – Axions appear as Nambu-Goldstone bosons in the PQ spontaneous symmetry breaking. let there be light – More generically, we speak about axionlike particles, to refer to fundamental (pseudo)scalars of similar properties without referring to a specific theory mode 2. Dark matter axions (as relics of Big Bang): – Axion Haloscopes ADMX@LLNlab, CARRACK@Kyoto 3. Axions produced in the laboratory Axion: a neutral very light (pseudo)scalar let there be axions COLD DM axion HOT DM axion – “Light shinning through wall” – Vacuum birefringence PVLAS@Legnaro; IPSS@Jlab OSQAR@CERN, ALPS@DESY; BMV@LULI;