Topics on Physics Beyond the Standard Model

Brane world mass unification of quarks and leptons: A brane world scenario based on the marriage of an early (TeV scale) quark-lepton unification model and the physics of large extra dimension is put forward in search of early quark-lepton mass relations. It employs one of the so-called Petite Unification scenarios, which are consistent with precise value of sin 2 θ W (M 2 Z ), namely PUT 2= SU(4) PS ⊗SU(3) L ⊗SU(3) H . The scenario possesses unusually charged chiral quarks and leptons in addition to the Standard Model fermions. Computation of mass scales for chiral fermions reveals mass relationships amongst quarks and leptons, and in particular between ordinary and unconventional fermions. In that sense, naturally light Dirac neutrinos are achievable for unconventional fermions lighter than 500 GeV, without any Majorana contribution through seesaw mechanism. Dark matter candidates from quantum zophodynamics: We present relic density calculation results for cold dark matter candidates from quantum zophodynamics, or QZD. As a model of dark energy and dark matter, QZD is an asymptotically free gauge theory with the gauge group SU(2) Z and a coupling constantα Z ∼ 1 at very low scale ofΛ Z ∼ 10 −3 eV whileα Z ∼ weak coupling at high energies. The dark matter candidates of QZD are two fermions in form of weakly interacting massive particles, whose relic densities would only depend on their masses. Our results show that for masses between 50 and 320 GeV, they can account for either a considerable fraction or the entire dark matter of the universe.

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