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

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

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

Neutrino Physics (theory)

Nonzero neutrino masses are the first definitive need to extend the standard model. After reviewing the basic framework, I describe the status of some of the major issues, including tests of the basic framework of neutrino masses and mixings; the question of Majorana vs. Dirac; the spectrum, mixings, and number of neutrinos; models, with special emphasis on constraints from typical superstring constructions (which are not consistent with popular bottom-up assumptions); and other implications.Comment: 13 pages, 6 figures, invited plenary talk at ICHEP200

The Chaotic Regime of D-Term Inflation

We consider D-term inflation for small couplings of the inflaton to matter fields. Standard hybrid inflation then ends at a critical value of the inflaton field that exceeds the Planck mass. During the subsequent waterfall transition the inflaton continues its slow-roll motion, whereas the waterfall field rapidly grows by quantum fluctuations. Beyond the decoherence time, the waterfall field becomes classical and approaches a time-dependent minimum, which is determined by the value of the inflaton field and the self-interaction of the waterfall field. During the final stage of inflation, the effective inflaton potential is essentially quadratic, which leads to the standard predictions of chaotic inflation. The model illustrates how the decay of a false vacuum of GUT-scale energy density can end in a period of `chaotic inflation'.Comment: 15 pages, 6 figures. v3: matches version published in JCA

The Neutrino Mass Window for Baryogenesis

Interactions of heavy Majorana neutrinos in the thermal phase of the early universe may be the origin of the cosmological matter-antimatter asymmetry. This mechanism of baryogenesis implies stringent constraints on light and heavy Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry in heavy neutrino decays which, together with the kinetic equations, yields an upper bound on all light neutrino masses of 0.1 eV. Lepton number changing processes at temperatures above the temperature T_B of baryogenesis can erase other, pre-existing contributions to the baryon asymmetry. We find that these washout processes become very efficient if the effective neutrino mass \tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial conditions is then erased. Hence, for neutrino masses in the range from (\Delta m^2_sol)^{1/2} \simeq 8*10^{-3} eV to (\Delta m^2_atm)^{1/2} \simeq 5*10^{-2} eV, which is suggested by neutrino oscillations, leptogenesis emerges as the unique source of the cosmological matter-antimatter asymmetry.Comment: 29 pages, 12 figures include

Some Aspects of Thermal Leptogenesis

Properties of neutrinos may be the origin of the matter-antimatter asymmetry of the universe. In the seesaw model for neutrino masses this leads to important constraints on the properties of light and heavy neutrinos. In particular, an upper bound on the light neutrino masses of 0.1 eV can be derived. We review the present status of thermal leptogenesis with emphasis on the theoretical uncertainties and discuss some implications for lepton and quark mass hierarchies, CP violation and dark matter. We also comment on the `leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in the range where leptogenesis works best.Comment: 23 pages, 5 figures, submitted to the Focus on Neutrino Physics issue of the New Journal of Physics, edited by F. Halzen, M. Lindner and A. Suzuk

Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses

We study the implications of thermal leptogenesis for neutrino parameters. Assuming that decays of N_1, the lightest of the heavy Majorana neutrinos, initiate baryogenesis, we show that the final baryon asymmetry is determined by only four parameters: the CP asymmetry epsilon_1, the heavy neutrino mass M_1, the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{m} of the light neutrino masses. Imposing the CMB measurement of the baryon asymmetry as constraint on the neutrino parameters, we show, in a model independent way, that quasi-degenerate neutrinos are incompatible with thermal leptogenesis. For maximal CP asymmetry epsilon_1, and neutrino masses in the range from (\Delta m^2_{sol})^{1/2} to (\Delta m^2_{atm})^{1/2}, the baryogenesis temperature is T_B = O(10^{10}) GeV.Comment: 28 pages, 14 figures included; v2: erratum added, M_1 lower bound in the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/