Soft Colour Interactions and Diffractive DIS

The basic ideas and some results of the semiclassical approach to diffractive DIS are briefly described. In the production of high-$p_{\perp}$ jets boson-gluon fusion is predicted to be the dominant partonic process. The $p_{\perp}$-spectrum and the two-jet invariant mass distribution provide a clear test of the underlying `hard' partonic process and the `soft' mechanism of colour neutralization.Comment: 6 pages, proceedings DIS 9

Leptogenesis with four gauge singlets

We consider a generic type of leptogenesis model which can successfully produce the correct value of the observed baryon number to entropy ratio. The main feature of this model is that it is a simple TeV scale model, a scale accessible in near future machines, with a minimal particle content. Both supersymmetric and non-supersymmetric versions of the model are feasible. This model also gives left-handed neutrino masses compatible with all current data from direct and indirect neutrino experiments.Comment: 13 pages, 9 PS figures, REVTe

Classical Limit for Scalar Fields at High Temperature

We study real-time correlation functions in scalar quantum field theories at temperature $T=1/\beta$. We show that the behaviour of soft, long wavelength modes is determined by classical statistical field theory. The loss of quantum coherence is due to interactions with the soft modes of the thermal bath. The soft modes are separated from the hard modes by an infrared cutoff \L \ll 1/(\hbar\beta). Integrating out the hard modes yields an effective theory for the soft modes. The infrared cutoff \L controls corrections to the classical limit which are \cO{\hbar\beta\L}. As an application, the plasmon damping rate is calculated.Comment: 24 pages, 7 eps figures, Late

Enhanced Symmetries of Orbifolds from Moduli Stabilization

We study a supersymmetric field theory in six dimensions compactified on the orbifold T^2/Z_2 with two Wilson lines. After supersymmetry breaking, the Casimir energy fixes the shape moduli at fixed points in field space where the symmetry of the torus lattice is enhanced. Localized Fayet-Iliopoulos terms stabilize the volume modulus at a size much smaller than the inverse supersymmetry breaking scale. All moduli masses are smaller than the gravitino mass.Comment: 24 pages, 10 figures, Appendix added, matches published versio

Calculating the diffractive from the inclusive structure function

It is demonstrated that the global properties of the rapidity gap events at HERA can be understood based on electron-gluon scattering and a non-perturbative mechanism of colour neutralization. Using the measured inclusive structure function $F_2$ to determine the parameters of the parton model, the diffractive structure function $F_2^D$ is predicted. The ratio of diffractive and inclusive cross sections, $R_D = \sigma_D/\sigma_{incl}\simeq 1/9$, is determined by the probability of the produced quark-antiquark pair to evolve into a colour singlet state.Comment: talk at Workshop on DIS and QCD, Paris, April 1995, 3 pages LaTeX, uses qcdparis.sty, 2 figures (uuencoded

Grand Unification and Subcritical Hybrid Inflation

We consider hybrid inflation for small couplings of the inflaton to matter such that the critical value of the inflaton field exceeds the Planck mass. It has recently been shown that inflation then continues at subcritical inflaton field values where quantum fluctuations generate an effective inflaton mass. The effective inflaton potential interpolates between a quadratic potential at small field values and a plateau at large field values. An analysis of the allowed parameter space leads to predictions for the scalar spectral index n_s and the tensor-to-scalar ratio r similar to those of natural inflation. Using the range for n_s and r favoured by the Planck data, we find that the energy scale of the plateau is constrained to the interval (1.6 - 2.4) * 10^16 GeV which includes the energy scale of gauge coupling unification in the supersymmetric standard model. The tensor-to-scalar ratio is predicted to have the lower bound r > 0.049 for 60 e-folds before the end of inflation.Comment: 5 pages, 3 figures, published version, a few typos are correcte

Flavour mixings in flux compactifications

A multiplicity of quark-lepton families can naturally arise as zero-modes in flux compactifications. The flavour structure of quark and lepton mass matrices is then determined by the wave function profiles of the zero-modes. We consider a supersymmetric $SO(10)\times U(1)$ model in six dimensions compactified on the orbifold $T^2/{\mathbb Z_2}$ with Abelian magnetic flux. A bulk $\mathbf{16}$-plet charged under the $U(1)$ provides the quark-lepton generations whereas two uncharged $\mathbf{10}$-plets yield two Higgs doublets. Bulk anomaly cancellation requires the presence of additional $\mathbf{16}$- and $\mathbf{10}$-plets. The corresponding zero-modes form vectorlike split multiplets that are needed to obtain a successful flavour phenomenology. We analyze the pattern of flavour mixings for the two heaviest families of the Standard Model and discuss possible generalizations to three and more generations.Comment: 28 pages, 3 figures, 3 table