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We construct supersymmetric SU(4)_C X SU(2)_L X SU(2)_R models with spontaneously broken left-right symmetry (C-parity). The minimal supersymmetric standard model (MSSM) can be recovered at low scales by exploiting the missing partner mechanism. The field content is compatible with realistic fermion masses and mixings, proton lifetime is close to or exceeds the current experimental bounds, and supersymmetric hybrid inflation can be implemented to take care of C-parity domain walls as well as magnetic monopoles, and to realize the observed baryon asymmetry via non-thermal leptogenesis., Comment: 10 pages

We construct a supersymmetric SU(2)_L X SU(2)_R X U(1)_B-L model in which a discrete symmetry (C-parity) implements strict left-right symmetry in the scalar (Higgs) sector. Although two electroweak bidoublets are introduced to accommodate the observed fermion masses and mixings, a natural missing partner mechanism insures that a single pair of MSSM Higgs doublets survives below the left-right symmetry breaking scale. If this scale happens to lie in the TeV range, several new particles potentially much lighter than the SU(2)_R charged gauge bosons W_R^+- will be accessible at the LHC., Comment: 12 pages, REVTex 4

We discuss fermion masses and mixings in models derived from orbifold GUTs such that gauge coupling unification is achieved without low energy supersymmetry by utilizing a non-canonical U(1)_Y. A gauged U(1)_X flavor symmetry plays an essential role, and the Green-Schwarz mechanism is invoked in anomaly cancellations. Models containing vector-like particles with masses close to M_{GUT} are also discussed., Comment: 18 pages

We discuss how unification of the gauge, Higgs and (three chiral family) matter superfields can be realized from the compactification of a six dimensional supersymmetric SU(8) gauge theory over the orbifold R^4 x T^2/Z_3. The bulk gauge interaction includes Yukawa interactions to generate masses for quarks and leptons after the electroweak symmetry is broken. The Yukawa matrices in this case turn out to be antisymmetric, and thus not phenomenologically viable. To overcome this we introduce brane fields which are vector-like under the standard model gauge symmetry, and so do not alter the number of chiral families. In such a setup, the observed fermion masses and mixings can be realized by taking into account suppression effects from the effective Wilson line couplings and large volume of the extra dimensions., Comment: 12 pages

Models with fermions in bifundamental representations can lead naturally to family unification as opposed to family replication. Such models typically predict (exotic) color singlet states with fractional electric charge, and magnetic monopoles with multiple Dirac charge. The exotics may be at the TeV scale, and relatively light magnetic monopoles (greater than about 10^7 GeV) can be present in the galaxy with abundance near the Parker bound. We focus on three family SU(4)XSU(3)XSU(3) models., Comment: 37 pages

We consider five dimensional (5D) supersymmetric SO(10) compactified on the orbifold $S^1/(Z_2\times Z_2')$ such that the SO(10) gauge symmetry is broken on both fixed points (branes), and the residual gauge symmetry is $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_X$. We explore one example in which the gauge symmetries on the two branes are respectively $SU(5)\times U(1)_X$ and $SU(4)_c\times SU(2)_L\times SU(2)_R$, and the MSSM gauge symmetry is recovered by the usual Higgs mechanism. We discuss how fermion masses and mixings can be understood in this framework by introducing a flavor $U(1)_F$ symmetry. Unification of the MSSM gauge couplings and proton stability are also considered. An order of magnitude increase in sensitivity could reveal proton decay., Comment: 1+23 pages, 2 figures, comments added, version to appear in NPB

We consider a 5D SUSY $SU(3)_c\times SU(2)_L\times U(1)_Y\times {\cal U}(1)$ model compactified on an $S^{(1)}/Z_2$ orbifold. To cancel anomalies arising from the presence of ${\cal U}(1)$, we employ a Chern-Simons term and also chiral fields which could reside on the brane or in the bulk depending on the model. The presence of ${\cal U}(1)$ symmetry leads to baryon number conservation, gives rise to matter parity, and permits satisfactory neutrino masses and mixings even for a low fundamental scale. The brane Fayet-Iliopoulos D-terms naturally break ${\cal U}(1)$, leaving N=1 SUSY unbroken in 4 dimensions., Comment: 17 pages, LaTex

Deviations from standard electroweak physics arise in the framework of a Randall-Sundrum model, with matter and gauge fields in the bulk and the Higgs field localized on the TeV brane. We focus in particular on modifications associated with the weak mixing angle. Comparison with the electroweak precision data yields a rather stringent lower bound of about 10 TeV on the masses of the lowest Kaluza-Klein excitation of the W and Z bosons. With some optimistic assumptions the bound could be lowered to about 7 TeV., Comment: 11 pages, 5 figures, comments and references added