中国科技论文在线 http://www.paper.edu.cn Preprint typeset in JHEP style - HYPER VERSION A4 flavour symmetry breaking scheme for understanding quark and neutrino mixing angles Xiao-Gang He NCTS/TPE, Department of Physics, National Taiwan University, Taipei, Taiwan, 10764, Republic of China E-mail:
[email protected] Yong-Yeon Keum NCTS/TPE, Department of Physics, National Taiwan University, Taipei, Taiwan, 10764, Republic of China E-mail:
[email protected] Raymond R. Volkas School of Physics, Research Centre for High Energy Physics, The University of Melbourne, Victoria 3010, Australia E-mail:
[email protected] Abstract: We propose a spontaneous A4 flavour symmetry breaking scheme to under- stand the observed pattern of quark and neutrino mixing. The fermion mass eigenvalues are arbitrary, but the mixing angles are constrained in such a way that the overall pat- terns are explained while also leaving sufficient freedom to fit the detailed features of the observed values, including CP-violating phases. The scheme realises the proposal of Low and Volkas to generate zero quark mixing and tribimaximal neutrino mixing at tree level, arXiv:hep-ph/0601001v4 10 Apr 2006 with deviations from both arising from small corrections after spontaneous A4 breaking. In the neutrino sector, the breaking is A4 Z2, while in the quark and charged-lepton → sectors it is A4 Z3 = C3. The full theory has A4 completely broken, but the two → ∼ different unbroken subgroups in the two sectors force the dominant mixing patterns to be as stated above. Radiative effects within each sector are shown to deviate neutrino mixing from tribimaximal, while maintaining zero quark mixing.