Flipping SU(5) Towards Five Dimensional Unification

It is shown that embedding of flipped SU(5) in a five-dimensional SO(10) enables exact unification of the gauge coupling constants. The demand for the unification uniquely determines both the compactification scale and the cutoff scale. These are found to be 5.5 \times 10^{14} GeV and 1.0 \times 10^{17} GeV respectively. The theory explains the absence of d=5 proton-decay operators through the implementation of the missing partner mechanism. On the other hand, the presence of d=6 proton-decay operators points towards the bulk localization of the first and the second family of matter fields.Comment: 21 pages, references added, 3 Postscript figures, ReVTeX

Non-commutative Euclidean structures in compact spaces

Based on results for real deformation parameter q we introduce a compact non- commutative structure covariant under the quantum group SOq(3) for q being a root of unity. To match the algebra of the q-deformed operators with necesarry conjugation properties it is helpful to define a module over the algebra genera- ted by the powers of q. In a representation where X is diagonal we show how P can be calculated. To manifest some typical properties an example of a one-di- mensional q-deformed Heisenberg algebra is also considered and compared with non-compact case.Comment: Changed conten

Proton Decay in Supersymmetric GUT Models

The instability of protons is a crucial prediction of supersymmetric GUTs. We review the decay in minimal supersymmetric SU(5), which is dominated by dimension-five operators, and discuss the implications of the failure of Yukawa unification for the decay rate. In a consistent SU(5) model, where SU(5) relations among Yukawa couplings hold, the proton decay rate can be several orders of magnitude smaller than the present experimental bound. Finally, we discuss orbifold GUTs, where proton decay via dimension-five operators is absent. The branching ratios of dimension-six decay can significantly differ from those in four dimensions.Comment: DESY report number correcte

On the Stability of the Classical Vacua in a Minimal SU(5) 5-D Supergravity Model

We consider a five-dimensional supergravity model with SU(5) gauge symmetry and the minimal field content. Studying the arising scalar potential we find that the gauging of the $U(1)_R$ symmetry of the five-dimensional supergravity causes instabilities. Lifting the instabilities the vacua are of Anti-de-Sitter type and SU(5) is broken along with supersymmetry. Keeping the $U(1)_R$ ungauged the potential has flat directions along which supersymmetry is unbroken.Comment: 24 pages, 2 figure

Charged currents, color dipoles and xF_3 at small x

We develop the light-cone color dipole description of highly asymmetric diffractive interactions of left-handed and right-handed electroweak bosons. We identify the origin and estimate the strength of the left-right asymmetry effect in terms of the light-cone wave functions. We report an evaluation of the small-x neutrino-nucleon DIS structure functions xF_3 and 2xF_1 and present comparison with experimental data.Comment: 11 pages, 3 figures, misprints correcte

Neutrino Democracy, Fermion Mass Hierarchies And Proton Decay From 5D SU(5)

The explanation of various observed phenomena such as large angle neutrino oscillations, hierarchies of charged fermion masses and CKM mixings, and apparent baryon number conservation may have a common origin. We show how this could occur in 5D SUSY SU(5) supplemented by a ${\cal U}(1)$ flavor symmetry and additional matter supermultiplets called 'copies'. In addition, the proton decays into $p\to K\nu$, with an estimated lifetime of order $10^{33}-10^{36}$ yrs. Other decay channels include $Ke$ and $K\mu$ with comparable rates. We also expect that BR$(\mu \to e\gamma)\sim$BR$(\tau \to \mu \gamma)$

Phenomenology of the General NMSSM with Gauge Mediated Supersymmetry Breaking

We investigate various classes of Gauge Mediated Supersymmetry Breaking models and show that the Next-to-Minimal Supersymmetric Standard Model can solve the mu-problem in a phenomenologically acceptable way. These models include scenarios with singlet tadpole terms, which are phenomenologically viable, e.g., in the presence of a small Yukawa coupling <~ 10^{-5}. Scenarios with suppressed trilinear A-terms at the messenger scale lead naturally to light CP-odd scalars, which play the r\^ole of pseudo R-axions. A wide range of parameters of such models satisfies LEP constraints, with CP-even Higgs scalars below 114 GeV decaying dominantly into a pair of CP-odd scalars.Comment: 24 pages, 6 figures, typos corrected, reference adde

Evolution of high-mass diffraction from the light quark valence component of the pomeron

We analyze the contribution from excitation of the $(q\bar q)(f\bar f),(q\bar q)g_1...g_n(f\bar f)$ Fock states of the photon to high mass diffraction in DIS. We show that the large $Q^2$ behavior of this contribution can be described by the DLLA evolution from the non-perturbative $f\bar f$ valence state of the pomeron. Although of higher order in pQCD, the new contribution to high-mass diffraction is comparable to that from the excitation of the $q\bar q g$ Fock state of the photon.Comment: 12 pages, 2 figures, the oublished version. The slight numerical errors corrected, all conclusions are retaine

Can Structure Formation Influence the Cosmological Evolution?

The backreaction of structure formation influences the cosmological evolution equation for the homogenous and isotropic average metric. In a cold dark matter universe this effect leads only to small corrections unless a substantial fraction of matter is located in regions where strong gravitational fields evolve in time. A``cosmic virial theorem'' states that the sum of gravitational and matter pressure vanishes and therefore relates the average kinetic energy to a suitable average of the Newtonian potential. In presence of a scalar ``cosmon'' field mediating quintessence, however, cosmology could be modified if local cosmon fluctuations grow large. We speculate that this may trigger the accelerated expansion of the universe after the formation of structure.Comment: new "cosmic virial theorem",new references,LaTex,11 page