Yukawa Couplings and Quark and Lepton Masses in an SO(10) Model with a Unified Higgs Sector

An analytic computation is given of the generation of Yukawa couplings and of the quark, charged lepton and neutrino masses in the framework of an SO(10) model with a unified Higgs sector consisting of a single pair of vector-spinor $144 + \overline{144}$ of Higgs multiplets. This unified Higgs sector allows for a breaking of SO(10) to the gauge group $SU(3)\times SU(2)_L \times U(1)_Y$ and contains light Higgs doublets allowing for the breaking of the electroweak symmetry. Fermion mass generation in this model typically arises from quartic couplings $16\cdot 16\cdot 144\cdot 144$ and $16\cdot 16\cdot \overline{144}\cdot \overline{144}$. Extending a previous work it is shown that much larger third generation masses can arise for all the fermions from mixing with 45 and 120 matter multiplets via the cubic couplings $16\cdot45\cdot\overline{144}$ and $16\cdot120\cdot144$. Further it is found that values of $\tan\beta$ as low as 10 can allow for a $b-\tau-t$ unification consistent with current data. The quartic and cubic couplings naturally lead to Dirac as well as Majorana neutrino masses necessary for the generation of See Saw neutrino masses.Comment: 34 page, 1 figur

PAMELA Positron Excess as a Signal from the Hidden Sector

The recent positron excess observed in the PAMELA satellite experiment strengthens previous experimental findings. We give here an analysis of this excess in the framework of the Stueckelberg extension of the standard model which includes an extra $U(1)_X$ gauge field and matter in the hidden sector. Such matter can produce the right amount of dark matter consistent with the WMAP constraints. Assuming the hidden sector matter to be Dirac fermions it is shown that their annihilation can produce the positron excess with the right positron energy dependence seen in the HEAT, AMS and the PAMELA experiments. Further test of the proposed model can come at the Large Hadron Collider. The predictions of the $\bar p/p$ flux ratio also fit the data.Comment: 9 pages,3 figures; Breit-Wigner enhancement emphasized; published in PR

The top quark electric dipole moment in an MSSM extension with vector like multiplets

The electric dipole moment (EDM) of the top quark is calculated in a model with a vector like multiplet which mixes with the third generation in an extension of the MSSM. Such mixings allow for new CP violating phases. Including these new CP phases, the EDM of the top in this class of models is computed. The top EDM arises from loops involving the exchange of the W, the Z as well as from the exchange involving the charginos, the neutralinos, the gluino, and the vector like multiplet and their superpartners. The analysis of the EDM of the top is more complicated than for the light quarks because the mass of the external fermion, in this case the top quark mass cannot be ignored relative to the masses inside the loops. A numerical analysis is presented and it is shown that the top EDM could be close to $10^{-19} ecm$ consistent with the current limits on the EDM of the electron, the neutron and on atomic EDMs. A top EDM of size $10^{-19}ecm$ could be accessible in collider experiments such as the ILC.Comment: 21 pages and 5 figues. Accepted for publication in Physical Review